Cylinders wall woes

[montuckymatt]

Just did my annual routine of pulling off my head on my flatty. It has low miles on new bore and rings. I had a keeper let loose and the connecting rod bushing move 1/8"out of the rod two summers ago. Left a nice finger nail gouge and I had to tear the motor apart. Here's a pic of the old damage
Here's what I found tonight. Engine has under 1000 miles on new bore,piston,rings,and connecting rod bushing +.002...I think

No ridges or Knicks that I can feel. Just the lines in the cylinder. Thoughts? I have my pistons set loose at .002-.003 since I do lots of high speed riding. It does slap a little in this cylinder when running.

[TriNortchopz]

My first thought was a ridge on the upper ring, but zooming in, can see the lines go to the top of the cylinder, above the upper limit of the top ring. Did the re-bore fully cleanup the cylinder wall damage?
Is the top of the piston flush with the top of the cylinder at TDC? Which pistons did you use and what did the manufacturer spec for clearance?

[JBinNC]

M,

Did you align the rods with the case decks after replacing the wristpin bushings? In my experience, you will NEVER be able to ream them exactly straight when doing them in place, and tweaking the rods is just part of the job. That's the first thing that came to mind when I saw the pic.

Jim

[docmel]

And where did the keeper go?

[montuckymatt]

I used the cast Eastern pistons and rings. They come flush to the top. No pop up. The bore was from std to .040. It cleaned up well.

I bought the tool and aligned the rod with case deck using the paper pull trick. Felt good and looked good.

I did notice the front rod has side to side play and was just about at the top of spec for movement. Up and down there was none. The rear rod had almost no side to side. I'm wondering if I need to dig deeper or if this is a just run it situation. I put alot of miles on this bike usually at 60-70mph.

The keeper got ground up and was in the screen on my cam chest. I pulled the engine apart and cleaned everything last winter. Luckily it stayed in big chunks and most was caught by the screen and some stayed in the bottom of the cases.

[Dragstews]

Something got in the chamber and found it's way to the piston...

In order to fix it, I see three ways ..

A) Bore it again. ( Oh Boy another new set of pistons !! )

B) Sleeve it. ( Get to keep the piston ya got in play )



C) Run it as is. ( A lost of some compression and perhaps a bit of oil smoke can be expected )

D) Find another jug that's under your bore size and bore it ..

[montuckymatt]

Thanks for all the replies. I'm leaning towards cleaning it up and running as is. I forgot to mention I do have an extra piston and set of rings the same size. What about a light hone and new piston/rings? Or would the benefits be negligible? It doesn't really smoke or show any signs of excessive blow by as of now.

[flatman]

How deep is the scoring? Remember its kinda of a band aid but you could hone and then knurl the piston. Also I think that there are some piston coatings that add a little (very little?) film on the skirts?

[JBinNC]

This would be choice E. That would be what I would favor, if the piston skirts are clean. I would hone the cylinder with a micro adjustable hone (Sunnen, Lisle, KwikWay, or what have you), NOT a spring glaze breaker or ball hone. I would gladly give up a half thou or thou of skirt clearance for a better cylinder wall finish, because the ring seal will be much better.

HOWEVER, and this is the big consideration, the piston skirts must be clean. Your fourth pic shows some light scoring at the piston thrust face area of the cylinder. That would give me pause. You need to pull the cylinders and inspect the piston skirts. If you see any embedded metal on/ in the piston skirts, that means a bearing is shedding metal somewhere.

You had a wristpin clip spit out, and that is usually a sign that a rod bearing is going bad, especially if it is on the rear cylinder. If one side of the rear rod rollers or crankpin starts to go bad, it will allow the rod to rock from side to side and force the wristpin against its clip until it spits it out. I have seen this over and over and over. Putting a new top end on, and not addressing the rods is a recipe for early failure.

Word to the wise is (usually) sufficient.
Jim

[montuckymatt]

This would be choice E. That would be what I would favor, if the piston skirts are clean. I would hone the cylinder with a micro adjustable hone (Sunnen, Lisle, KwikWay, or what have you), NOT a spring glaze breaker or ball hone. I would gladly give up a half thou or thou of skirt clearance for a better cylinder wall finish, because the ring seal will be much better.

HOWEVER, and this is the big consideration, the piston skirts must be clean. Your fourth pic shows some light scoring at the piston thrust face area of the cylinder. That would give me pause. You need to pull the cylinders and inspect the piston skirts. If you see any embedded metal on/ in the piston skirts, that means a bearing is shedding metal somewhere.

You had a wristpin clip spit out, and that is usually a sign that a rod bearing is going bad, especially if it is on the rear cylinder. If one side of the rear rod rollers or crankpin starts to go bad, it will allow the rod to rock from side to side and force the wristpin against its clip until it spits it out. I have seen this over and over and over. Putting a new top end on, and not addressing the rods is a recipe for early failure.

Word to the wise is (usually) sufficient.
Jim

Well we just got a ton of snow and it's 1 degree out. I have plenty of garage time to pull the cylinder and dig deeper. I'll post pics when I get it off

[montuckymatt]

I took some pics today.

And now the A side...
And the some more..

[montuckymatt]

And a few inside the cases..

[montuckymatt]

How deep is the scoring? Remember its kinda of a band aid but you could hone and then knurl the piston. Also I think that there are some piston coatings that add a little (very little?) film on the skirts?

I can't feel the scoring with my finger nail. I can see it but can't feel it.

[Dragstews]

There's where the piece of crap got stuck ...

... /// https://youtu.be/Qsr5063uOUY \\\ ...

[flatman]

Yea but why does the scoring line run all the way to the top of the cylinder and not just stop shy of the top where the rings are? Enquiring minds want to know. This kinda stuff is always a mystery.

[DustyDave]

Yea but why does the scoring line run all the way to the top of the cylinder and not just stop shy of the top where the rings are? Enquiring minds want to know. This kinda stuff is always a mystery.

As I understand it once the trash starts a gouge the sharp, rough edges of the gouge damage the rings and the top and bottom of the piston which extends the gouge. then the ring with the attached trash rotates because of the off center drag from the trash and damage and the process starts over.
Dusty

[flatman]

I would think the piston being aluminum and softer would not extend the groove in the cast iron cylinder since the piece looks embedded in the piston. Also with that piece of trash stuck in the ring and ringland it sure looks like ALOT of gap between the ring and the ring groove. A new set of pistons at least? Also since flatheads tend to run alittle hotter (or so I have been told) seems like 2 to 3 clearance is not enough, but you said you were experiencing piston slap. I thought 4 was the minimum for cast, at least thats what Truet and Osbourne told me for my stroker 45 piston clearance but the motor has not run yet. But, again, I am no motor builder, nor expert. Only armchair quarterbacking. LOL Looks like a bit of work in any case. Hone and fit some 50 over pistons? maybe spiral locks for the piston pin?

[DustyDave]

Cut one of those galled knots on the piston apart they are embedded with iron flakes! Even with pistons that say to fit tighter I've never had any luck fitting a flat head tighter than .004. The way I ride .005 seems to be minimum. Fit the front .0005 or so looser than the rear.
Dusty

[JBinNC]

Cut one of those galled knots on the piston apart they are embedded with iron flakes! Even with pistons that say to fit tighter I've never had any luck fitting a flat head tighter than .004. The way I ride .005 seems to be minimum. Fit the front .0005 or so looser than the rear.
Dusty

I have a reprint of an old, contemporary article on race-prepping a K model. The recommended skirt clearance for the stock pistons was .007. I find the 45s with loose fit cast pistons do go "tink tink tink" when they are running. It's a very distinctive sound. I don't have any experience of the big flatties.

In this case, I think I would hone, with a micrometer adjustable hone, and fit the same size new piston & rings at a little looser skirt clearance. I don't see any metal swarf on the piston skirts in the pics, apart from the chunk that D. pointed out. So I think the rod & main bearings are OK. But it would be prudent to pull this motor apart and clean it thoroughly, along with the oil tank, lines, & etc. I have been called upon to do the same on a fresh shovel motor with wierd skirt damage, in an abundance of caution. It's a pity to pull a fresh motor back down, but probably worth it in the long run. No telling what the original rebuilder may have done. It's just time & money after all.

Jim

[montuckymatt]

I checked my spec sheet from the machine shop and my piston to bore clearance is .003. I do have a spare new .040 piston and rings. This piston is .0001 larger max OD than the one currently in use. Re-hone and cleanup sounds good to me. We still have a ton of snow and I've got the time....thanks for all the answers so far.