sticky valves?

[Jeanie]

It's possible that my plane experienced a stuck valve today - on a warm engine the run up seemed fine and then when I applied power to take off it shook like it was going to come apart... so I aborted the take off, taxied around and repeated the run up - might be a fouled plug I thought to myself... shook like crazy again so I leaned it out and waited for it to see what it would do... throttle back to 1,000 seemed fine throttle to 1700 shook... then it just smoothed out. Morning sickness maybe except the plane had been flown already for 1.5 hrs this morning before the weirdness. After it smoothed out it then ran at full power quite happily and behaved as normal no other strangeness - We stayed over the field for a bit to make sure and then went to the practice area.

I thought I'd pull the bottom plugs tomorrow morning and see how they look - oil in one maybe or some big lead rocks that just won't go away... and hold my hand over the openings, pull the prop through and feel for compression.

Anyway, if it was a stuck valve and I"m thinking it must have been what can be done about it? Get my A/P to take it apart and clean the offending area? replace it? I'm a little worried frankly as I just started w/ primary students today and I sure don't want an engine to eat a valve and have a real emergency.

Thanks!

 

[Trapper John]

What engine make and model?

 

[Jeanie]

Lycoming O-235 L2C in a Cessna 152

 

[Tom-D]

Lycoming O-235 L2C in a Cessna 152

How many hours since last ovhl.?

has the wobble check been done recently?

When was the last plug cleaning?

Your engine may be running too rich, if it fouls plugs quickly.

 

[Jeanie]

How many hours since last ovhl.?

~~~~~~~~~ 1600 SMOH and 200 STOH

has the wobble check been done recently?

~~~~~~~ don't have a clue I'll ask Bill the A/P tomorrow - what's a wobble check?

When was the last plug cleaning?

~~~~~~~ about 20 hrs ago roughly

Your engine may be running too rich, if it fouls plugs quickly.

~~~~~~ I usually lean the stuffing out of it for ground ops and know where it should be for T/O - I operate out of a 4500 ft elev field and today was at a field w/ 3,000 MSL elev. And, yes, by virtue of the fact that I have the mixture pulled out about 1.5 inches it may be set wrong but it's always been fine till today

The compression checks for the last annual dated December 2010 were 67-74-76-72 over 80

The top was completed Nov. 2008 - the comp checks for the last annual at 93.5 hrs STOH were 78-78-79-78 over 80 which is significantly different in just one years time and 100 hrs use.

 

[Tom-D]

~~~~~~ I usually lean the stuffing out of it for ground ops and know where it should be for T/O - I operate out of a 4500 ft elev field and today was at a field w/ 3,000 MSL elev. And, yes, by virtue of the fact that I have the mixture pulled out about 1.5 inches it may be set wrong but it's always been fine till today

The compression checks for the last annual dated December 2010 were 67-74-76-72 over 80

The top was completed Nov. 2008 - the comp checks for the last annual at 93.5 hrs STOH were 78-78-79-78 over 80 which is significantly different in just one years time and 100 hrs use.

weard stuff happens, you are close to the 100Hour suggested plug cleaning.

compressions mean nothing to valve guides, unless they are really bad, at your next inspection have service bulletin completed to see how much wear you have.

http://egaa.home.mindspring.com/engine1.htm

 

[Let'sgoflying!]

Jeanie, lean it on the ground (ie when taxiing only), til it is about to quit. Starve it.
Lean normally for all other ops (I think this was discussed before).

 

[Dan Thomas]

The O-235 is famous for fouling the bottom plugs. We've had the -K2C version foul plugs in 25 hours. These engines run pretty cool and don't keep the plugs clean at all and I think the plugs are too close to the bottom side of the chamber where lead runs into them too easily.

Finally got around it by installing REM37BY plugs; they have extended electrodes that are almost foul-proof. No more hassles.

REM 37BY on the left, REM38 or 40 (actually a long-reach RHM) on the right. The 37's well is really shallow and with the electrodes sticking up they don't get filled with the crud that shorts them. Champion's website can tell you whether the 37's are approved for whatever engine model you might have. The 37's are approved, and indeed recommended by Champion, for the O-235-L2C. http://www.championaerospace.com/assets/AV-14-Jan2010.pdf

Dan

 

[Jeanie]

Great, Thanks everybody - I'll check the plugs that are being used - I think they be the REM37BY plugs but I'll check again.

And, I'll talk w/ my A/P about the service bulletin too today.

 

[somorris]

I wouldn't think the shaking would be from the plugs. I would lean towards the valves also, like your original assumption. They can be cleaned, but it is kind of a pain.

 

[Jeanie]

I flew the plane up to Odessa yesterday to the mechanic. Did compression checks - all good. Pulled the plugs and looked thru his boroscope and think we saw a nice white straight scratch in the back left cylinder wall. Broken ring maybe - hence the new oil dripping from the breather and the very wet plug. there was oil on the piston and the top plug in the front right cyl. too and he thinking that's a loose valve guide... he's pulling the covers on Monday and checking the guides etc. He also said, he's pretty sure that the severe shaking was a stuck valve as it didn't change for one mag vs. both ... and it finally cleared up completely. He's going to check to see how tight they feel and clean it up.
On the first run up yesterday it took a while to clear but on the run up before I left for ODO it seemed fine.....
Anyway, it's in process, Thanks ya'll for your help - I'll let you know how it turns out

 

[Dan Thomas]

I flew the plane up to Odessa yesterday to the mechanic. Did compression checks - all good. Pulled the plugs and looked thru his boroscope and think we saw a nice white straight scratch in the back left cylinder wall. Broken ring maybe - hence the new oil dripping from the breather and the very wet plug. there was oil on the piston and the top plug in the front right cyl.

The O-235 is known for corrosion troubles in the cylinders (condensation because the engine runs too cool) and that corrosion leads to the rings wearing the cylinder and leaving a ridge at the bottom of the ring travel. That ridge is sharp and it shaves aluminum off the piston pin guide plugs. Aluminum chips in the screen or filter is are the tipoff. If the plug wears enough the piston pin starts cutting a "nice straight scratch" in the side of the cylinder, parallel to the piston travel, and, actually, usually two parallel scratches from the top and bottom edges of the pin end.

The front cylinders are usually the worst, since they get the full blast of cooling air and run the coldest.

Might be faced with cylinder rework.

Dan

 

[Jeanie]

I figured that the cyliders might need to be rehoned... Good info on the possible cause of the "scratch". I'll ask my A/P about it.
Lovely.

 

[Jeanie]

OK, so he pulled 2 of them and they had corrosion on the inside of them... seems that they will need to be reworked... maybe even chromed if clearing them out leaves them too wide for spec. So, I"ll get to break in some chromed cylinders.

And, the one valve did have some gunk in the guide too from what he said. He planned to pull the other 2 cylinders this evening to see how they look.

Now, get this.... They were just reworked Oct 2008 and only have 133 hrs on them. It's desert here not swamp so I don't understand how it's possible that they could have signif. corrosion. I have heard that it's a good idea to open the oil dipstick to let it breath and put a paper towel in it to keep stuff out so that moisture won't condensate in it... I've never done that maybe I'll start.

 

[Clark1961]

I have heard that it's a good idea to open the oil dipstick to let it breath and put a paper towel in it to keep stuff out so that moisture won't condensate in it... I've never done that maybe I'll start.

I generally open the oil filler cap and put a rag over it when I park it in the hangar. I figure it can't hurt and the oil filler cap doesn't get as "gunky".

 

[Tom-D]

OK, so he pulled 2 of them and they had corrosion on the inside of them... seems that they will need to be reworked... maybe even chromed if clearing them out leaves them too wide for spec. So, I"ll get to break in some chromed cylinders.

And, the one valve did have some gunk in the guide too from what he said. He planned to pull the other 2 cylinders this evening to see how they look.

Now, get this.... They were just reworked Oct 2008 and only have 133 hrs on them. It's desert here not swamp so I don't understand how it's possible that they could have signif. corrosion. I have heard that it's a good idea to open the oil dipstick to let it breath and put a paper towel in it to keep stuff out so that moisture won't condensate in it... I've never done that maybe I'll start.

Send all 4 to Charley Malot, have him bore to the next size over and rebuild as required with new pistons and rings, DO NOT Chrome them. or you'll be sorry.

 

[Jeanie]

I wondered about chroming them and what that would mean. It's a bad thing is it?

 

[Tom-D]

I wondered about chroming them and what that would mean. It's a bad thing is it?

Chroming is a process that adds chrome to the interior of the cylinder reducing the bore to standard again. Chrome is very hard, and in many cases the rings will not seat. and you have an engine that has a very high oil usage.

 

[Dan Thomas]

Now, get this.... They were just reworked Oct 2008 and only have 133 hrs on them. It's desert here not swamp so I don't understand how it's possible that they could have signif. corrosion. I have heard that it's a good idea to open the oil dipstick to let it breath and put a paper towel in it to keep stuff out so that moisture won't condensate in it... I've never done that maybe I'll start.

The moisture isn't from the air. The burning of fossil fuels produces many gases, among them water vapor, and the rings can't prevent all the gases from escaping into the crankcase. "Blowby," we call it, and when water vapor gets into a crankcase it'll condense there and on the cylinder walls and mix with the oil until the engine gets hot enough and stays hot long enough to boil it off through the breather tube. A cold engine has larger clearances, allowing more blowby, and short flights make the whole situation a lot worse. If that water mixes with the oil and sits for awhile, it catalyzes with the oil in the presence of the metals and forms acids that eat your engine even quicker than just water. That's where your cylinder pitting comes from.

The O-235 runs cool and is known for corrosion troubles. Put a blocking plate over the oil cooler to get the oil temps up, and avoid short flights. Run it hard. Change the oil often.

Dan

 

[Ted]

The cylinders were redone 2.5 years ago, but how old are they overall? I'd check the prices on rework vs. buying new cylinder kits - you might be surprised.

 

[N801BH]

I agree with Ted... Lately, alot of cylinder rebuilds seem to be costing more then new cylinders. We had the same issue in the heavy truck market 20 years ago.All the shops set up to do the rebuilds could not compete with the up and coming mass volume recon industry and today almost all those little mom and pop shops are long gone. The aviation side is apparently headed down the same road. IMHO

Ben.

 

[Ted]

I agree with Ted... Lately, alot of cylinder rebuilds seem to be costing more then new cylinders. We had the same issue in the heavy truck market 20 years ago.All the shops set up to do the rebuilds could not compete with the up and coming mass volume recon industry and today almost all those little mom and pop shops are long gone. The aviation side is apparently headed down the same road. IMHO

For a long time, new cylinders cost a lot of money (well, ok, they're still not cheap, but they're a lot cheaper than they were). Tom used the example of Charlie Merlot for cylinder overhauls. I'm told he does great work, but the last numbers I recall Tom saying for an overhaul per cylinder were more than I paid for my new cylinder kits. When I called up that shop for quotes on overhauls on the 520s, they were by far the most expensive with the slowest turnaround time.

It's worth shopping around and deciding what you think is the best option for your plane.

 

[Jeanie]

Thanks ya'll, I'll check into just getting new ones - I really don't want chrome. And I'll ask Bill about blocking the oil cooler to some degree... it does get awful hot here in summer.

 

[Tom-D]

For a long time, new cylinders cost a lot of money (well, ok, they're still not cheap, but they're a lot cheaper than they were). Tom used the example of Charlie Merlot for cylinder overhauls. I'm told he does great work, but the last numbers I recall Tom saying for an overhaul per cylinder were more than I paid for my new cylinder kits. When I called up that shop for quotes on overhauls on the 520s, they were by far the most expensive with the slowest turnaround time.

It's worth shopping around and deciding what you think is the best option for your plane.

When you consider the cost of machine time to bore, then buy new pistons, piston pins, rings, valves, guides, springs, keepers, aren't you getting new? at about the same price? the reason to do the overhaul of old cylinders is because you know the history of the cylinders and know there are no ADs on them, and won't be in the near future.

The reason to chrome is way different than many think. We chromed because the cylinders were worn beyond boring them again and staying with in the new piston/ring size. the first time we overhaul, we go to the next over size piston, so the supply of standard size pistons never got depleted. So we ran out of over sized first. and needed a way to go back to standard.

The bad thing about chrome is the chrome is very hard, and the rings can't seat with out wearing out first. so in many cases it takes several sets of rings to wear the bore smooth enough to stop oil consumption. Plus the fact you can't use a chrome ring in a chrome cylinder, as many did with disastrous results. The rough chrome on the cylinder wall tears the chrome off the rings and sends it to your main bearings and ruins your crank, by embedding its self in the soft bearing material and cutting a groove in the crank.

Chrome is a necessity in some antique engines not so the Cont/Lyke flat engines, we now have new cylinders at the same costs as a chromed cylinder with half the problems.

 

[Tom-D]

Now, get this.... They were just reworked Oct 2008 and only have 133 hrs on them. It's desert here not swamp so I don't understand how it's possible that they could have signif. corrosion. I have heard that it's a good idea to open the oil dipstick to let it breath and put a paper towel in it to keep stuff out so that moisture won't condensate in it... I've never done that maybe I'll start.

corrosion pitting isn't the big boogy man that many folks think it is, the cylinder wall material gets converted from iron, to iron oxide during the corrosion process, that oxide falls out into the oil and is carried away, leaving a hole in the wall we call a pit. That pit will fill with oil when the piston is above it, then the rings pass over the pit as it goes toward the bottom of the cylinder on the power stroke, and scrapes away the excess oil leaving the pit full of oil that gets burned during combustion, leaving a carbon deposit in the pit, which gets polished smooth on the up stroke, and the process is repeated until the pit fills with carbon. Making carbon in this manor (heat and pressure) is the first stage of making a diamond. the carbon is very hard.
This is the reason we do the cross hatch pattern during the honing of a cylinder, hoping the scratch will fill with hard carbon and stop wear. and it has been proven to work.

 

[Capt. Geoffrey Thorpe]

Thanks ya'll, I'll check into just getting new ones - I really don't want chrome. And I'll ask Bill about blocking the oil cooler to some degree... it does get awful hot here in summer.

Burned exhaust from a gasoline engine contains a bit less than 15% water by weight (180mg/L at nominal temperature / pressure).

Blow-by volume varies from about .5% to 5% of the total intake flow and is a mix of unburned and burned fuel / air mixture.

Crankcase concentration data from an engine with a PCV system at various operating conditions:
CO2 0 – 3%
NOx 0 – 60 ppm
H2O 10 -90 mg/L
O2 14-19%
The PCV system dilutes the crank case gasses so aircraft engines will have higher levels of H2O, CO2, etc. Blow-by also contains sulphate and nitrate ions which can turn into sulfuric and nitric acids in the crank case.

Blow-by also includes a lot of unburned fuel which can dilute your oil.

At room temperature, air can hold about 17mg/L of water; so clearly, there will be condensation inside the engine every time you shut down.

So, what do you do?

Running the engine long enough to get the oil hot will help drive out any excess water that has been accumulating – that's the standard recommendation. Engines that run only short times and don't warm up are just going to build up more and more water and icky stuff. But even a good and hot engine will have some condensation after shut down.

If you want to be a hero and make the world a better place (at least as far as engine durability is concerned) come up with a crankcase vent system that flows fresh air through the engine and get an STC. (Aircraft engines do not have the manifold vacuum available that you have in automotive applications.) Failing that, for a wet sump engine like yours, you could stick an aquarium pump in the dip stick tube (or breather tube with the dip stick loose) and let it push fresh air through the engine while it is shut down – the water and fuel adsorbed in the oil will eventually evaporate. For a dry sump engine, you would have to figure out an inlet / outlet for the air that may or may not involve the dipstick.

Note: External humidity doesn't really play much a factor in what is in the crankcase. But the warmer the environment, the faster corrosion happens. You probably want to store your airplane in Alaska when you aren't using it.

 

[Tom-D]

B
At room temperature, air can hold about 17mg/L of water; so clearly, there will be condensation inside the engine every time you shut down.

If you would like to know if there is enough water in your oil to do damage to the engine try this.

when the engine is cold, start it run it 1 minutes, then shut down, and pull the dip stick, if the oil looks like chocolate milk, change it right there, right then. because all the water will be in suspension.

dry sump engines and little Continentals ignore this trick, you have a a tank that will not deliver water to the engine.

 

[Ted]

When you consider the cost of machine time to bore, then buy new pistons, piston pins, rings, valves, guides, springs, keepers, aren't you getting new? at about the same price? the reason to do the overhaul of old cylinders is because you know the history of the cylinders and know there are no ADs on them, and won't be in the near future.

You're not getting new, though, it's still overhauled. The cylinder bores and heads still have hours and millions of stress cycles, including at the critical junction where the head screws on to the barrel. Yes, theoretically they should have unlimited life, but that doesn't mean that they haven't been through those cycles and may or may not have had some stress item, impurity in the casting, etc. that may rear its ugly head. Sure, it could come up with a new one also, and you can make an argument either way, but the new one doesn't have as many cycles on it. Plus if you're honing the old cylinders, there is a question of where you are relative to limits. Also if it's a nitrided cylinder, you've honed away that nitrided coating, and with it a lot of the stiffness that came with it.

A previous history of no ADs is also no guarantee of no future ADs, since ADs pop up all the time.

There are other questions, too. What's your warranty? Are you getting a new OEM vs. new aftermarket, and which aftermarket company. That makes a difference.

As with so many things in aviation, "It depends." I'm not sure what I'll do with cylinders on the 310 when we have to overhaul the engines. I do know what I did on the Aztec, and have been happy with.

 

[Tom-D]

You're not getting new, though, it's still overhauled.
Some times the devil you know, isn't as bad as the devil you don't know, and with the Cylinders made off shore and their AD list, I'll take low time cylinders that have proven them selves.


The cylinder bores and heads still have hours and millions of stress cycles, including at the critical junction where the head screws on to the barrel. Yes, theoretically they should have unlimited life, but that doesn't mean that they haven't been through those cycles and may or may not have had some stress item, impurity in the casting, etc. that may rear its ugly head. Sure, it could come up with a new one also, and you can make an argument either way, but the new one doesn't have as many cycles on it. Plus if you're honing the old cylinders, there is a question of where you are relative to limits. Also if it's a nitrided cylinder, you've honed away that nitrided coating, and with it a lot of the stiffness that came with it.

A previous history of no ADs is also no guarantee of no future ADs, since ADs pop up all the time.

There are other questions, too. What's your warranty? Are you getting a new OEM vs. new aftermarket, and which aftermarket company. That makes a difference.

As with so many things in aviation, "It depends." I'm not sure what I'll do with cylinders on the 310 when we have to overhaul the engines. I do know what I did on the Aztec, and have been happy with.

You are absolutely correct, it is a big decision with plenty options and considerations.

 

[Tom-D]

Thanks ya'll, I'll check into just getting new ones - I really don't want chrome. And I'll ask Bill about blocking the oil cooler to some degree... it does get awful hot here in summer.

I do not know if ECI makes cylinders for your 0-235, but if they do, thy have a exhaust valve rotators that is worth the bucks.

http://www.eci.aero/pages/products_titan.aspx

 

[Ted]

Some times the devil you know, isn't as bad as the devil you don't know, and with the Cylinders made off shore and their AD list, I'll take low time cylinders that have proven them selves.

You're correct, and that's why there are a lot of variables. Do I trust my old cylinders, and why do I trust them? Why would I not trust my new ones?

You are absolutely correct, it is a big decision with plenty options and considerations.

Yep.

One thing that was very insightful was a chat I had with Western Skyways about their warranty policies and recommended cylinders for different engines. Their recommendation was basically as follows:

- "D" rocker big bore Continentals: ECI
- 421s: Factory Continental
- Parallel valve 4-cylinder Lycomings: ECI or Factory
- All other Lycomings: Factory

They said through their experience, those had the best service with fewest warranty claims or other repairs. I think that most of their business ends up being in the larger 6-cylinder engines, though.

 

[Tom-D]

You're correct, and that's why there are a lot of variables. Do I trust my old cylinders, and why do I trust them? Why would I not trust my new ones?
because the old cylinders were built right here in America from virgin materials, the new ones are built off shore from recycled aluminum/steel. and have developed a reputation of being junk.

Yep.

One thing that was very insightful was a chat I had with Western Skyways about their warranty policies and recommended cylinders for different engines. Their recommendation was basically as follows:

- "D" rocker big bore Continentals: ECI
- 421s: Factory Continental
- Parallel valve 4-cylinder Lycomings: ECI or Factory
- All other Lycomings: Factory

They said through their experience, those had the best service with fewest warranty claims or other repairs. I think that most of their business ends up being in the larger 6-cylinder engines, though.

in that respect, I only know my experiences, and my only engine from hell was a Skyways engine.

 

[Ted]

because the old cylinders were built right here in America from virgin materials, the new ones are built off shore from recycled aluminum/steel. and have developed a reputation of being junk.

Which cylinders for which engines from which manufacturers? You've got a high variability from factory to aftermarket, which factory to which aftermarket, and which engines they're going on as cylinder designs and loads change.

Old cylinders built here in America from virgin materials have millions of cycles on them. That could mean that they're going to fail between now and the next overhaul due to some little crack developing where the head screws onto the barrel, or it could mean that they'll live indefinitely.

in that respect, I only know my experiences, and my only engine from hell was a Skyways engine.

As can I. You've also had bad experiences with Lycomings, and I haven't, nor has my mechanic (this is averaging out, since everything has a problem at some point). Of course, my mechanic thinks Continentals are made out of concentrated evil, and I haven't had bad experiences from the Continentals I fly. I like them just fine.

 

[dmccormack]

Of course, my mechanic thinks Continentals are made out of concentrated evil, and I haven't had bad experiences from the Continentals I fly. I like them just fine.

That's funny...

One A&P/IA I know loves to talk about how much easier Continentals are to work on, how much more support, how much more professional, blah, blah, blah...

My current A&P thinks everything is equally lousy.

 

[Ted]

That's funny...

One A&P/IA I know loves to talk about how much easier Continentals are to work on, how much more support, how much more professional, blah, blah, blah...

My current A&P thinks everything is equally lousy.

Personally I think it's the Chevy/Ford argument. Yeah, each one has its weak points. I like my Ford better than the Chevys I used to have. Is either one really better than the other? No, I think they're all about the same. Each of us has had whatever experiences we've had that make us like or dislike one more than the other. And at the end of the day, we probably just end up with whatever makes the most sense for us to own or use.

 

[Let'sgoflying!]

What is the latest word on NiCarbide cylinders. The barrel finish, that is (ignoring any other defects the manufacture might have produced in those cylinders.)
Do they hold up?
Can you still get them? Is it an option for Jeanie?

 

[Tom-D]

My current A&P thinks everything is equally lousy.

That's the guy that got it right.

 

[Tom-D]

Which cylinders for which engines from which manufacturers? You've got a high variability from factory to aftermarket, which factory to which aftermarket, and which engines they're going on as cylinder designs and loads change.

the AD history is all you need to look up to see when the junk started to appear, then notice the ink stamps on the new parts you get, even from the OEM.


Old cylinders built here in America from virgin materials have millions of cycles on them.
Not the ones worth overhauling

That could mean that they're going to fail between now and the next overhaul due to some little crack developing where the head screws onto the barrel, or it could mean that they'll live indefinitely.

As can I. You've also had bad experiences with Lycomings, and I haven't, nor has my mechanic (this is averaging out, since everything has a problem at some point). Of course, my mechanic thinks Continentals are made out of concentrated evil, and I haven't had bad experiences from the Continentals I fly. I like them just fine.

You are kicking a boogy man that doesn't exist, it is vary rare that a cylinder will crack or have a head separation under 3k hours of service, If the time is unknown on any cylinder I would not have it overhaulled, repaired maybe, depending upon the discrepancy.

we have carried this topic way off course the OP already noted she has had her cylinders overhauled and got very poor usage from them, which says to me there is more to this than meets these pages.

 

[Dan Thomas]

corrosion pitting isn't the big boogy man that many folks think it is, the cylinder wall material gets converted from iron, to iron oxide during the corrosion process, that oxide falls out into the oil and is carried away, leaving a hole in the wall we call a pit. That pit will fill with oil when the piston is above it, then the rings pass over the pit as it goes toward the bottom of the cylinder on the power stroke, and scrapes away the excess oil leaving the pit full of oil that gets burned during combustion, leaving a carbon deposit in the pit, which gets polished smooth on the up stroke, and the process is repeated until the pit fills with carbon. Making carbon in this manor (heat and pressure) is the first stage of making a diamond. the carbon is very hard.
This is the reason we do the cross hatch pattern during the honing of a cylinder, hoping the scratch will fill with hard carbon and stop wear. and it has been proven to work.

In the O-235, at least, I have found water droplets between the piston and cylinder when I pull the cylinders off to deal with the pitting/ridging/pin plug shaving issue. When aluminum and iron get together in the presence of water, that iron will suffer, and those pits become so big and so numerous that the rings really start shaving off the iron, enough to get that ridge at the bottom of the travel. At that point it's unlikely that the cylinder can be rehoned to standard limits, and oversizing becomes necessary.

Dan

Dan

 

[Tom-D]

In the O-235, at least, I have found water droplets between the piston and cylinder when I pull the cylinders off to deal with the pitting/ridging/pin plug shaving issue. When aluminum and iron get together in the presence of water, that iron will suffer, and those pits become so big and so numerous that the rings really start shaving off the iron, enough to get that ridge at the bottom of the travel. At that point it's unlikely that the cylinder can be rehoned to standard limits, and oversizing becomes necessary.

Dan

Dan

What are you using for oil? bacon grease?