[mrunderhill1975a]

I am still moving forward with this project bike.  It has a noise, I thought it was a ping, however, I have retarded the spark as far as I can, and the noise is still there.  The noise can be heard at low rpm under load (like a ping).  I am now concerned that it is a piston slap.

For some background, this bike has a aluminum barrel which I don't think was stock.  The previous owner installed the alloy barrel, I don't know what piston was used with this cylinder.

Any suggestions about how I can verify it is a piston slap or not?

[Bullet Whisperer]

My tuned 350 uses a cast off piston from one of the racing engines, it is a Meteor Minor Sports piston, with nearly 1" removed from the bottom of the skirt and well worn. There is a lot of piston slap, especially while at lower rpm, which can easily be heard in this video, if you want a comparison. The bike has done thousands of miles like this and I don't worry about it
 B.W.

 https://www.youtube.com/watch?v=RBPg_Xj2X04

[ace.cafe]

Usually a piston slap is noticed when the engine is cold, and quiets down after it is warmed up. This is common if a forged piston is installed, and the bore was made a little too big.

If it happens mostly after it is hot, you may have a bearing noise. Quite common to have stock bearings go bad after installing  an aftermarket piston, especially if it is a heavy piston.
The other common problem from piston replacement could be too much compression, which can cause ping that you can't retard away.

Do a cold cranking compression test with the throttle held wide open. That will tell you if they set the compression correctly.

[guss,guss]

what does this sound like?

https://www.youtube.com/watch?v=CH5xpwVNiIk

 i installed a 535 kit W/8.5:1 piston. no spacer plate. i thought it was a clearance issue but now not sure.  don't mean to hijack but this may help mrunderhill or others.

[mrunderhill1975a]

Ok, just tested the compression cold, wide open throttle, cold engine, elevation 5200ft asl. The result was 103 psi.

I get the noise, which is most similar to the noise in the GussGuss video, when hot or cold, low RPM pulling a hill.  The noise is reduced when opening throttle and increasing RPM.  I will try to get a video or sound recording.

[ace.cafe]

Ok, just tested the compression cold, wide open throttle, cold engine, elevation 5200ft asl. The result was 103 psi.

I get the noise, which is most similar to the noise in the GussGuss video, when hot or cold, low RPM pulling a hill.  The noise is reduced when opening throttle and increasing RPM.  I will try to get a video or sound recording.

Okay, at 5200 ft elevation, you probably are not going to get pinging, and especially not with 103 psi compression. Unless the engine is overheating for some reason. So, that's most likely okay.

The sound that I am hearing on the Guss Guss video sounds like it could be a bearing.It probably wouldn't hurt to pull the head and barrel to check out the con rod for up/down play, also noting if there is any play whether it is coming from the big end, or perhaps the main bearings.
It's fairly easy to do that for an internal test. Probably be apart and back together in an afternoon.

Guss Guss needs to also do a compression check, because if there is a high compression piston in there with no spacer under the barrel, and it still has the stock cams in the normal timing position, then it is probably too high compression if it is anywhere near sea level elevation.

[malky]

As all that is said + if your project is a keeper and you don't know it's history a thorough check can only be a good thing for piece of mind. Decent main bearings aren't that expensive etc.

[Bullet Whisperer]

what does this sound like?

https://www.youtube.com/watch?v=CH5xpwVNiIk

 i installed a 535 kit W/8.5:1 piston. no spacer plate. i thought it was a clearance issue but now not sure.  don't mean to hijack but this may help mrunderhill or others.

Hi Guss Guss. That sounds like a valve gear related noise to me. Perhaps a valve is just touching the piston going over tdc on the overlap - I have seen it more than once and I don't know if you use one, but there are incorrectly marked 3 way timing pinions out there, where the 'retarded' marks are more advanced than the 'advanced' ones    Is there any slop in the timing gear train? The noise definitely sounds like a half engine speed noise to me, my 350 piston slap noise is a lot faster, as you would expect 
 B.W.

[ace.cafe]

Whichever it may be, it seems like getting the top end off to check it out would be a good idea.

[guss,guss]

 I'm going to start a new topic for my bullet. looking back i feel like it was rude to ask for advise before mrunderhill had his worked out. thanks for the advise and i can use more advise from you gearheads.

[mrunderhill1975a]

Quoting ACE:
"Also, cut open the oil filter and see if you can notice any white metal swarf in it, which would indicate the floating bush coming apart, or shiny steel bits which would indicate the main bearings disintegrating."

After opening the filter, I found one flat piece of white metal swarf, approximately 1mm by 1mm.  I assume this means a total teardown is in order?