Crack in cylinder? + bronze flakes in cylinder

[johnpaul44]

RV7 O-360 A1A 900 hours

Today was in the process of borescoping all the cylinders and i think i have discovered a crack in the spark plug hole of number 4 cylinder.. im not sure if its just lead debris that made it look like a crack or what.. is there anyway to tell 100% without removing the cylinder?

In addition to this i have been getting bronze flakes in my oil... when looking into this cylinder i notice bronze flakes all over the place, but not present in other cylinders , maybe this cylinder is completely trashed?

 

[riobison]

I had one like that. Do a leak down test and see what you have. Mine still passed but when I sprayed soapy water on the top of the head, I had bubbles. Removed the cyl to find a crack from the exhaust valve to the plug.

Tim

 

[Marc Bourget]

Casting Artifact?

The path of material inflow in the mold, during the casting process - in this case, flowing around the cores for the valve port and plug (the plug may cast solid) may "meet" in a line between the two cores. If the casting material is hot enough it meets and mixes resulting in a uniform density.

It could be that the inflowing material cooled a little too much - resulting in a cold joint - visible as a "line." (The casting facility may use another word),

If this is the case, and it may not leak as described in the other post, keep your eye on it as I suspect it may be a stress riser or weak point.

 

[lr172]

Yes, trashed or at a minimum needs an O/H.

Hard to say if that is a crack or not, but my guess is that it is, as that is probably the most likely place for a crack. Either way, that has to come off. Given the cyl is full of bronze flakes, there is a good chance you have a valve guide coming apart and that needs immediate attention, though there is a possibility that it is a small end rod bushing that is shedding it's material (quite uncommon). If you take a pic of the guides, you can probably see the damage/wear in the guide.

They can use a dye penetrant at O/H to determine if that is actually a crack or not.

Larry

 

[Mike S]

Given the cyl is full of bronze flakes, there is a good chance you have a valve guide coming apart and that needs immediate attention, though there is a possibility that it is a small end rod bushing that is shedding it's material (quite uncommon).

Larry

I think Larry got it. Rod/pin bushing trash should not end up inside cylinder.

 

[johnpaul44]

Thanks all for the responses so far, admittedly i have asked a few other places and been told that removing is a last resort and such. However, i now feel like i have multiple issues here (compression test showed leaking intake valve, maybe a crack ?, bronze/brass metal in cylinder)

Looking for a sanity check here, I'm not crazy for wanting to remove the cylinder and replace with a new cylinder or at least fix the issue? It seems those local to me prefer a much more laissez-faire approach and to keep running it.

Im wondering how long the wait is for new cylinders ? i heard there way quite the backlog last year

 

[Mike S]

compression test showed leaking intake valve, maybe a crack ?, bronze/brass metal in cylinder

Intake--yep, exhaust guide debris should get pushed out the tail pipe.

Have you tried removing the rocker cover and checking the valve & guide for damage, play, etc?

 

[Dan 57]

Have you tried removing the rocker cover and checking the valve & guide for damage, play, etc?

Yep, good one from Mike. Proceed as if you were doing a SB388C. You could even drop the valve(s) into the cylinder for a real look at the guide(s).

OTOH the forward portion of the guide can be inspected when the respective valve is set fully open, by inserting and angling your borescope the right way, but I doubt you’ll see anything meaningful.

As for the crack, difficult to say for certain. The ones I’ve seen had dark edges, but identifying if it is a crack, or not, certainly worth doing.

 

[riobison]

I was down to 72/80. Being half deaf I couldn't be sure what I was or wasn't hearing. I called a local AME over and he gave me a hand. After a few minutes he suggested that we spray some soapy water around the cylinder. Bubbles started coming out the top of the head through the fins. Obviously at this point the cylinder came off and found a very fine hair line crack between the exhaust valve and spark plug.

 

[mahlon_r]

Looks like a crack. Regardless the crack is the least of your problems. Metal in the oil filter with "bronze flakes all over the place" in the cylinder are cause for concern and should be investigated.
How old in calendar years is this engine? Is it possible you have old style bronze piston pin plugs? That might explain the bronze flakes in the cylinder and filter, if one of them was going bad. Regardless, it is necessary to investigate the bronze flakes in the oil and cylinder. Cylinder removal is necessary to investigate the flakes. Easy to check out if its a crack with the cylinder off. Are the bronze flakes in the oil, bronze color on one side and aluminum color on the other? If so could be a bearing delaminating.
Good Luck,
Mahlon

 

[johnpaul44]

The engine was built in 2001, however in 2003 two of the cylinder were replaced with overhauled cylinders, it has a total of about 900 hours on it. Im not sure on the piston plugs it could be possible they are the older style.

The bronze/brass flakes im seeing do not have aluminum on the other side, they are pure bronze/brass that goes for whats in the cylinder and what i have found in the oil filter. My oil analysis has also always showed completely normal levels.

Looks like a crack. Regardless the crack is the least of your problems. Metal in the oil filter with "bronze flakes all over the place" in the cylinder are cause for concern and should be investigated.
How old in calendar years is this engine? Is it possible you have old style bronze piston pin plugs? That might explain the bronze flakes in the cylinder and filter, if one of them was going bad. Regardless, it is necessary to investigate the bronze flakes in the oil and cylinder. Cylinder removal is necessary to investigate the flakes. Easy to check out if its a crack with the cylinder off. Are the bronze flakes in the oil, bronze color on one side and aluminum color on the other? If so could be a bearing delaminating.
Good Luck,
Mahlon

 

[johnpaul44]

Sounds like the consensus is the cylinder should be removed, i have heard plenty about the dangers of doing this so i want to be 100% sure its done correctly. I will also have an A&P help me. but i have some questions for the group:

1. I intend to purchase torque plates (https://ryanaircrafttools.com/products/1598). Should these torque plates be applied after the cylinder is removed? and the plate torqued to the full torque?
2. should i purchase new nuts when torque the plate down or can i reuse the old ones and buy new ones for when the cylinder goes on?
3. Does the opposite cylinder need to be retorqued when applying the torque plate?

Finally i deicded to pull the rocker arms for inspection and i noted some scoreing? in the bushing, i can feel it catch on a plastic scraper how much is too much here? maybe i should just order a new cylinder at this point

 

[PCHunt]

In addition to brand new cylinder assemblies, many engine overhaul shops sell overhauled/rebuilt cylinders. Somewhat less expensive.

 

[hgerhardt]

With the oil contaminated with debris, you really ought to take the whole engine apart and do an IRAN. It's not that hard, and in the end you'll know exactly what went wrong. By just doing the top end, you're hoping that the bottom end is sound. Besides, it's been 22 years since overhaul...it's time to take it apart.

I don't know about you, but hope is not good enough for me to rely on to make uninterrupted power in MY airplane.

 

[johnpaul44]

Thanks all, So im taking the cylinder off and will be having a A&P help me put on a cylinder next week. I have a few questions:

1. I noticed some play in the through bolt case studs, is some play normal here? see video : https://imgur.com/a/vdOeQs7

2. Took some pics of my cam shaft, i dont think there is any spalling or other issues could you guys take a look? https://imgur.com/a/4YSLsJy

3. Finally i cannot get the piston pin out of the cylinder, it seems firmly stuck are there any tricks to getting it out? i tried heating it as well as some lube

 

[PCHunt]

I'll chime in, with the following caveat: I am NOT an engine guru by any means.
There are several highly experienced engine folks on this forum, and I hope they will also chime in.

IMHO: the "wobbling" you show in your video is NOT normal!

A couple of years ago I replaced all 4 cylinders on my O-360 with Overhauled and Yellow Tagged rebuilt cylinder assemblies, and all studs seemed to be solid.
My suggestion would be to get an opinion from a REPUTABLE engine overhaul shop, or an engine "guru"*before proceeding.

My opinion, FWIW.

 

[lr172]

1. I noticed some play in the through bolt case studs, is some play normal here? see video : https://imgur.com/a/vdOeQs7

e

No, not normal. Is it wide deck or narrow deck? Either way it needs to be dealt with.

 

[riobison]

I just changed 4 of them on an o320. No, that movement is not normal.

 

[johnpaul44]

update

update, so finally had some time to take the cylinder apart further, i noted the exhaust valve slide right out fo the guide, but the intake valve would not come out of the guide.. had to tap it out. Pulling the intake valve out the last bit i heard metal to metal scraping. Seems like something was going on with the intake valve has i notice some metal scoring in the guide .

Intake valve almost looks burned? from the back do they normally get build up like this?