Engine Knock

[Lechy]

What Hillsy said is quite correct the tappet screws do peen over and cause a bad reading. The last time I adjusted the tappets on my 800 I competely removed the screws and re-ground the domes using a whet stone. The 750/800's do develop a slight clunk which no one has ever tracked down successfully a small consensus think it may be caused by a worn wrist pin but it has never been proven.

[rocksandhammers]

Reviving this thread because I finally have some progress and I think I've found the culprit of the noise I was hearing. Been slowly digging my way into the top end. Finally got the flywheel rotor off today and noticed something by the front camchain. The engine casing right in front of the chain had chipped off.




The broken bit had fallen out onto my workbench, and when I looked at it there were scratches in the metal from the chain.



I'm amazed that the piece didn't find it's way further into the engine and really grenade it. Going to have the broken off bit welded back in and hope for the best. My local mechanic who helped me get the rotor off said it should be fine welded in since it's not a moving part or anything other than a guide.

I guess my question is, what could have caused the cam chain to hit this enough to break it off? The mechanic said it was an issue with the cam chain tensioner, but if I recall correctly this engine doesn't have a cam chain tensenior? What do you guys think?

[hillsy]

Every engine with a cam chain has some sort of tensioner.

This is yours (#7 and #11):



If it were me I'd just leave it and not worry about getting it welded - it is just webbing and will not do any harm by leaving it out.

Has this bike been worked on? A cam chain that does that would probably have skipped a tooth or more and cause a ton of top end damage?

[Designer]

In looking at your Piston pictures of Mon Oct 19, 2020, I don't see anything that looks like A Ton Of Top End Damage.
So it seems that Skipping a Tooth on the Cam Gearing might not be the source of your Knocking.

However, I would take some time and look into your Cam Tensioning. Look well at the Spring Tensioners themselves, and check the Wear Patterns on the Plastic Guides.

[hillsy]

In looking at your Piston pictures of Mon Oct 19, 2020, I don't see anything that looks like A Ton Of Top End Damage.

I didn't mean NOW - I meant has this engine been worked on previously. If the cam chain has bunched up to such a degree to smash that webbing then it's possible the cam has jumped some teeth in the past and that could cause top end damage. That piece of web might have been sitting in there for years un-noticed even after a top end rebuild.

If this is the original engine (IE: not rebuilt) and if that damage hasn't caused the top end to grenade go and buy yourself a lottery ticket.

And the problem will be with the tensioner and the guides if that is the case.

EDIT: Just had a look at the pics where you pulled off the cylinders but can only really see the rear cylinder camchain guides - which look good. Assuming the front are the same there's only the tensioner left to inspect / suspect.

[Designer]

In looking at your Piston pictures of Mon Oct 19, 2020, I don't see anything that looks like A Ton Of Top End Damage.

I didn't mean NOW - I meant has this engine been worked on previously. If the cam chain has bunched up to such a degree to smash that webbing then it's possible the cam has jumped some teeth in the past and that could cause top end damage. That piece of web might have been sitting in there for years un-noticed even after a top end rebuild.

This makes no sense.

If the Cam Chain had bunched up, skipped a tooth, broken off the web-part, caused,. A Ton Of Top End Damage,...necessitating an engine rebuilding. Then the rebuilt was run afterwards, then was it taken apart to show the undamaged pistons pictured.......why would the Broken Web Part that caused the Ton Of Top End Damage that caused the rebuild still be in the rebuilt engine?

[rocksandhammers]

As far as I know I’m the first person since the factory to crack into the engine. Bike had 17,000 miles on it before I got it, and I don’t know any of the history really since I got it at a dealer. But I haven’t seen anything while digging into it to suggest it has been rebuilt prior to now.

Thanks for pointing out the tensioners hillsy. I’ll check them out next time I can get out in the garage for a bit.

[hillsy]

In looking at your Piston pictures of Mon Oct 19, 2020, I don't see anything that looks like A Ton Of Top End Damage.

I didn't mean NOW - I meant has this engine been worked on previously. If the cam chain has bunched up to such a degree to smash that webbing then it's possible the cam has jumped some teeth in the past and that could cause top end damage. That piece of web might have been sitting in there for years un-noticed even after a top end rebuild.

This makes no sense.

If the Cam Chain had bunched up, skipped a tooth, broken off the web-part, caused,. A Ton Of Top End Damage,...necessitating an engine rebuilding. Then the rebuilt was run afterwards, then was it taken apart to show the undamaged pistons pictured.......why would the Broken Web Part that caused the Ton Of Top End Damage that caused the rebuild still be in the rebuilt engine?

rocksandhammers has just pulled down the entire top end without taking off the stator rotor and discovering the broken webbing - it would be quite possible for someone else to do that as well. Don't worry - I've worked in a few shops and seen a lot of fucked up shortcuts....

Anyway, sounds like from the low mileage when he got the bike that this is unlikely.

Get yourself a lotto ticket rocksandhammers

[rocksandhammers]

Get yourself a lotto ticket rocksandhammers

It was probably a bit of luck, but based on past experience that's usually in short supply for me. I'd like to think some of it has to do with me paying attention as well. I've put close to 30,000 miles on the bike in only a few years, so I noticed the odd noise coming from this section of the engine right away. The bike was still running fine for the most part, but I basically decided to tear into the engine as soon as I heard the noise because I was worried it was the prelude to something worse happening. Glad I listened to my gut on this and didn't keep pushing it.

[WintrSol]

Looking closely at the first photo, the damage on the casting appears to imply that the break was towards the chain, not knocked to the left. Most specifically, the arc in the upper part of the break. I wonder if it was a casting flaw which eventually broke off, hitting the chain and causing the knocking sound?
Although the broken bit says kind of the opposite - that it was hit most strongly near the bottom, causing it to angle away from the casting. Something I would study more closely, looking for evidence of micro-cracks. The pattern of damage is elusive in only two photos.

[rocksandhammers]

Looking closely at the first photo, the damage on the casting appears to imply that the break was towards the chain, not knocked to the left. Most specifically, the arc in the upper part of the break. I wonder if it was a casting flaw which eventually broke off, hitting the chain and causing the knocking sound?
Although the broken bit says kind of the opposite - that it was hit most strongly near the bottom, causing it to angle away from the casting. Something I would study more closely, looking for evidence of micro-cracks. The pattern of damage is elusive in only two photos.

There are actually two broken pieces. There's a smaller bit that I didn't include in the picture. I think the break could have occurred in the middle of the two bits, causing them to fold inward and causing that edges to break away towards the chain, if that makes sense. I'll definitely give it a good looking over to see if I find any other cracks though.

[hillsy]

The witness marks on the broken piece of web are quite deep. It looks like it was hit pretty hard from the chain side (like from a bunched up chain).

Are you sure you didn't try and force the crank at any time when you had the heads off? If that damage has happened when the bike was running due to the chain being that slack the top end would be toast.

[Designer]

The broken bit had fallen out onto my workbench, and when I looked at it there were scratches in the metal from the chain.

I see there are a couple of "types" of scratches on the Broken Piece pictured.

The shallower ones near the bottom show scratches in them as if the chain was scraping on the piece at that point and wearing on it in a somewhat wide pattern .

The Scratches just above those are a smaller in surface area, and bit deeper and more "defined".

Then there is the Deep Gouge(s) to the right of those.

I speculate that those Gouge(s) happened when the piece came loose/off and got hit/wedged against the fast-moving chain.

[rocksandhammers]

The witness marks on the broken piece of web are quite deep. It looks like it was hit pretty hard from the chain side (like from a bunched up chain).

Are you sure you didn't try and force the crank at any time when you had the heads off? If that damage has happened when the bike was running due to the chain being that slack the top end would be toast.

It’s totally possible. I tried to be real careful about not letting the chains bunch up or anything, but with this being my first time I certainly wouldn’t rule out. Trying to remember any situations that might have resulted in this and not coming up with much, but it has taken me a year to get this far and I’ve killed some brain cells during that time… haha

[Designer]

It’s totally possible. I tried to be real careful about not letting the chains bunch up or anything, but with this being my first time I certainly wouldn’t rule out. Trying to remember any situations that might have resulted in this and not coming up with much, but it has taken me a year to get this far and I’ve killed some brain cells during that time… haha

Help me out here, are you saying you had the Heads off (and of course, put back on) and rode the Bike?

If so, did the "knock" you report happen after that?

[rocksandhammers]

It’s totally possible. I tried to be real careful about not letting the chains bunch up or anything, but with this being my first time I certainly wouldn’t rule out. Trying to remember any situations that might have resulted in this and not coming up with much, but it has taken me a year to get this far and I’ve killed some brain cells during that time… haha

Help me out here, are you saying you had the Heads off (and of course, put back on) and rode the Bike?

If so, did the "knock" you report happen after that?

No, removed the engine from the bike last summer. Slowly making my way through the top end. I haven’t put it back together or anything during that time. Just taking my time with things.

[Designer]

No, removed the engine from the bike last summer. Slowly making my way through the top end. I haven’t put it back together or anything during that time. Just taking my time with things.

Thanks for such a quick response.

To me, It seems like you had taken off the Heads, and were trying to be,....." real careful about not letting the chains bunch up or anything,"....when you were re-assembling the Motor.

I'm trying to be a .."Sherlock Holmes".... to help you out.

[hillsy]

By the way - what are these marks from? A bunched up camchain, perhaps?