Camchain Tension

[Miti]

I cocked up tensioning the front chain on my V1000 a few weeks ago and Dave Snr was most helpful with his advice on the matter... The unbelievable rattle from that cyl was also a clue..!!

Now a little fine tuning....

I'm 100% certain that my valve timing is set correctly and that the valve clearances are in spec... But there is still a VERY noticeable rattle from both pots... Louder on the front, but definitely from both...

It's much louder on the timing side of the engine than the clutch side and appears to be coming from the chain casings (i.e. it's the chains rattling).

After re-setting the tension on the front pot (and noting Mick's sage advice that the tension MUSTN'T BE TOO TIGHT and that tensioner blades are "NLA") I noted that the chain didn't stay tight through the entire revolution of the engine... There's definitely a "slack spot" (maybe more than one).

So... Could someone "in the know" please advise... Should a correctly tensioned chain be tight across the whole revolution of the engine?  Or are slack spots normal...

Or, I suppose, am I looking at new timing chains over the winter..?

Ta!

Miti

[Rob B]

The chain will be slack at top dead centre on the firing stroke and tight at top dead centre on the valve overlap stroke. The piston only has to be approximately at TDC on the firing stroke when you check the chain tension so stick a long screw driver down the plug hole and turn the engine gently(with both plugs out) by rotating the rear wheel in 5th gear. Once you have found the correct Top Dead Centre, which is the one where the chain is slack, then this will be the best position to reset the chain tension. If you are still not certain then remove the cam covers and check that the cam follower buckets are free to turn.

Good luck,

Robert

[Miti]

Thanks Rob.

Mine are definitely tightened at the right point - TDC Firing stroke, both pots and he chain tension at that point seems fine... The problem is that the chain doesn't stay tight as the engine is rotated... It starts tight and then loosens... Maybe a couple of times per complete revolution...

The tensioner blades seem fine, M8 allen bolts are tight... It's as if he chains have tight/slack spots and I'm petty sure that it's this tightening/loosening tht is causing the "rattle" from my engine...

It certainly seems to be running well enough...  But it's pretty noisy, even for a Hesketh..

Miti

[Rob B]

Hi,

That is as it should be. At some points the valve springs and buckets acting agaisnt the cam lobes will be forcing the inlet cam sprocket clockwise and the exhauast sprocket counterclockwise. At these points you will have even more "apparent" chain slack than when you set it correctly as outlined below. But don't touch it!

Worth checking the valve clearences? The ones in the book are far too large and the engine will sound even more like a bag of spanners. I run my engines with 0.05mm inlet and exhaust. Mick generally sets them up with zero clearenece with the buckets just free to spin.

Cheers,

[Dave Snr]

Rob is correct, the cams opening and closing the valves have a significant effect on the apparent chain tension. You can only really access the chain between the cam sprockets to check tension. During the compression stroke and firing stroke there are no valves open, so the chain will be slack and should be uniformly slack throughout - As Rob says, TDC on the firing stroke is smack in the middle and the best point to adjust the chain. At the end of the firing stoke the exhaust valve opens which puts a lot of tension on the drive side of the chain and gives more apparent slack between the sprockets. At the end of the exhaust stroke the exhaust valve is closing and the inlet opening. The spring on the exhaust valve as it closes will be rotating the chain against the opening inlet valve. So at this point the chain between the sprockets will be very tight. So if that is your "tight spot", don't worry about it as the chain slack is now out of your view on the long runs down the Sock.

Valve clearances - Rob's 0.05mm is 0.002 thou inch, in old units and is what I set mine to as well. Mick's EN10 story says 0.001 to 0.002 thou inch for both valves, but as long as the buckets are free to spin when checked cold, then all is OK as the clearances increase when the engine is hot.
Dave H

[Miti]

Thanks guys...

I've checked the valve clearances and they're all pretty darn close to the 0.05mm spec... Additionally, the sound is only really coming from the timing side of the engine, so I'm convinced it's the chains...

Looks like earplugs are the order of the day then...

Miti