The Stovebolt Site Forums The Shop Area Engine Shop Cylinder wear pattern

This is a cylinder photo of a vintage British bike I'm working on.The guy brought it over, said it runs strong, but smokes, fix it.You can't see the pistons here, but they look fairly new, he said the bike only has a few thousand miles on rebuild.Looks like it wasn't honed ,but the bike owner said he saw the cylinders before they were installed, had a cross hatch hone patteren.I'm gonna pull the cylinders anyway, but I have never seen a wear pattern like this. Looks like the rings were skidding, you can just almost feel the marks, the piston fit appears ok.A hone will clean it up, fit new rings, still a wierd pattern
Cylinders

That is odd. I wonder if maybe the ring gap was too close or may be wrong ring, too thin for the piston groove, rolling against the land.

I don't know for sure, the local machinist suggested the last boring was done off center and out of round,and a poor quality hone job didn't true it up.

Is that bad crankshaft bearing fit? My guess is shortly after you do your good work he's going to have the same problem. It looks like the piston and ring sets (1st tme pistons good fit, assumed same for new rings) were chattering on the compression exhaust stroke.

Cos, I don't know for sure but the bike has good oil pressure at a hot idle, ran smoothly with no unusual noises, and the rods have no excessive play.The pattern is consistent all the way around on both cylinders.The ring fit on the pistons is good, better than most from my experience.
I just pulled the cylinders, measured them with a quality verniers, everything seems within a .001 of an inch. I'm headed for the machine shop for a proper measurement with his bore gauges.The customer is not goona be happy if I wack him with a $500 bill plus labor for replacement cylinders and new pistons. That's what happens when you take shortcuts on a high rpm, high output engine(by vintage standards) .The engine can go one more oversize to .060, but depending on the Bike's use, the cylinders may become too thin,distort, and shorten engine life.

Tony let us know what you find out.

What was the ring end-gap of the rings you removed?

chip

Chip, the ring gap is .011,on a bore of just less than 3 inches, within specs. These old air cooled engines run loose piston and ring clearances to prevent siezures when run hard.
The machinist said the bores weren't prepped correctly, The boring tool was dull, leaving excessive machining marks and the honing didn't remove them. He suspects the honing was done with a "bottle brush" deglazer, not a rigid stone type hone.Looks like a correct hone job will clean it up, only remove another thousands of an inch.The present piston to wall clearance is .004, with .0055 being prefered for this engine. This photo show evidence of very slight scuffing on the piston thrust face from too tight a clearance probably. Pistons Should be ok with a honing ,fit new rings and hopefully good to go.

Tony,

Are those oiling holes drilled in the oil ring land? Shouldn't they be deburred? Doesn't look like who ever bored them paid much attention to detail. . . would bug me to see the burrs and I would have tried to clean them up a little.

I'm pretty rusty from lack of recent use, but it looks like the guy who was asked to use a hone thought they said bone so rubbed his forehead on it instead. That's terrible! Almost as bad as my attempt at humor...

Looks like a bad bore-job. (with a dremel)

Tony Looks like the person that bored the engine was to close to the piston size. That would not leave material to hone a good finish and fit them right Dave

Ken, more like a marginal deburring job, the camera has a hard time picking up sharp lines.I believe these are Japanese or Italian made pistons,both of them produce the best bike parts. I guess Guido and Saki were smoking a joint instead of deburring the holes.

Tony,

This looks looks like I'm seeing tooling marks. BUT, you said that the person saw them hone it, so that rules that theory out. This cylinder looks good about3/4 of the diameter and that might be why it feels good when you move the top of the piston back and forth.

Do you by chance have a mill that you can bolt the block down to the table and swing an indicator? If so, dail in the bore in the middle (where ever you think there is minimun wear, of the bore)

Then check the very top of the cylinder with the indicator without moving the mill table, it should have an area near the very top where the rings have never touched or have worn due to that the top piston ring doesn't go all the way to the top. There should be maybe at least an 1/8 inch there. Thus, should be an origainl factory machine area and "dead nuts" in the center of the original bore. UNLESS, the ring groove or some call it a ridge groove had been removed too when it was re-bored. Compare the two reading

From the picture the area I am talking about looks like it "MAY" be original. I have seen times where some people try to just hone a real worn and already out of round cylinder and this leaves it way out of round along with taper in the bore, then they can't get a new set of rings to seat in, if they do it doesn't last long. this might be the case here.

Like most, I machine the bore first to "straightened out" the bore and leave a few thousanths to hone out to take off any "hi's" left behind by the machining and then to smooth up the finish and give it that cross-hatch mark.

My guess is If the did indeed machine the cylinder, they machined it out of center and hit it with a hone and sent it on it's merry way. I have seen it done in other "SO-CALLED" machine shops before. I have even seen it go as far as running a bead hone or some call them a ball hone through em. I usually only use these type of hones to break any glazing due to a poor break-in.

Let us know, this has me wondering, but I still think it's "out of center" and/or "out of round"

Good luck,

John

John,the cylinders were bored all the way through,less than a half a thousands variation, at least when I measure it.I have a quality honing tool,I'll run it through to get the proper finish, then have the machinist check it carefully, he owes me a favor,lol.
Ralphy, yes ,you can do that.Back when I raced these things,I had a blown set of cases for bolting the cylinders to for finish honing.Found out the cases distorted to the cylinder when bolted down, at least on the Triumphs I raced.The rings are cast or nodular iron for street use.
The Triumphs I dragged used to spit out the gasket between the cylinders and crankcase, engine stress caused the iron cylinders and aluminum cases to squirm around even when bolted tighly together.These were 1930's engine designs ,reliable when they were 500 cc's and 28 HP at 5500 rpm. By the 60's they were 650's with 52 HP at 7200 rpm, same basic engine design, not as reliable.When racing,the bike made about 60 HP at 7500 rpm in a "legal" state of tune for the class I was in.Then the new at the time, 4 cylinder 750 Honda got in my class at the strip, I pushed the Triumph even more to stay ahead,wilder cams,rpms raised to 8200.Made them Honda guys mad!!!Then in 73 the New 900 Kawasaki pretty much sent me to the vintage racing classes.

Tony,

OK, now we know that your 100 percent that the engine was bored correctly. So this leads to another thought, just today in the shop we had a BIG piston.

First I got a question for you. What did the piston skirt look like on the opposite side of the piston on the top?

The reason I am asking, I'm not a ("quote")engine machinist, but a regular repair machinist. I have seen many many STUPID things done on engines and everything else that comes along in the past almost 20 years. BUT, still machine work is machine work, the two go hand in hand and specs. are specs. .0001" on and engine is still .0001" on a bearing area.

ANYHOW, One of our other machinist was working on a VERY large piston about 10 inch in diameter from an engine for a natural gas pipe line distributing station. (regular engine machine shops don't work on these big beast) Anyhow, this piston started locking up and showing a mark on the bottom (skirt) and then another marked area on the top opposite side of the skirt. After we (not myself) took the piston and measured it all up, everything was in their specs. BUT, We found out that the piston itself wrist pin bore was bore at an angle about .015" from parallel from the top, bottom and side of the piston. The bores were both straight with one another, just bored at an angle to the piston. In return it was causing it to "cock" in the cylinder bore.

This gas companies maintenance crews know when something is not going together correct. From what I gathered as they were installing the piston etc. Pistons fit in the bore great, just when the connecting rod was installed on the piston and on the crank shaft everything was getting extremely tight and could not rolled it over, but they could not definatly locate the cause of the problem.

That's when it came to our shop and we discovered this small problem. They found out that 2 of the 6 pistons wrist pin bores were bore this way. Probably just from the factory's setup fixture.

Back to this engine, I don't know all the particulars of the engine (Stroke or HP), but I know the valves are HUGH. I just reground the valve seat faces, here a couple weeks ago. 4 inches in diameter on the vale itself and a overall length of 20 inches and the stem is about 1-1/8 in diameter.

I would just love to have an old burnt valve for a conservation piece and/or a door stop, LOL!

FOOD for Thought, THIS IS ONE OF THEIR SMALLER ENGINES!

This is JUST a thought, after seeing this one today. I know you said the piston were new or close to new and that you have cheked them, but have you thought of a bad wrist pin bore? Honestly speaking, it's probably one thing I don't check on building a new engine.

My guess is that it's probably somthing real simple, more than a mis-aligned wrist pin bore, like here, but ya never know.

Just had to share this story with you.

John

John, yes, I'm thinking still it's the poor hone job.Both pistons have the same slight wear patterns and these bikes don't use offset piston pins, so the pistons aren't installed backwards.I have a new bore gauge coming so I can check it out for myself.If I have to push the limits on the piston clearance to get a clean hone job, it'll be ok according to my past experience with British bikes.I'm also going to try Deves rings, they are steel alloy, not cast, supposed to be superior to even Moly rings, especially for demanding conditions.