no tensioner left - floppy decomp '04>

i was doing a '04 650 yesterday and the camchain tension is completely used up! it's fully open. the chain, an IWIS is like new still. i suspect the chain has been rattling around. what i could do with is an old style tensioner with the blob on the end right now.....

i also checked and the auto decomp has been smacking hell out of the tiny bolt, it's almost 'D' in section yet it still hasn't broken - miraculouosly!!!! a floppy decomp makes a:clack! clack! clack! noise at very low revs as the blob bangs between the stop bolt and it's resting place.

the spring seems to be soft. now i don't do '04s everyday, infact it's only my 4th but interestingly, it's the third one with no tension adjustment left? now that has got to be a worry!

if not this, the only year that the quality IWIS chain was fitted (and it still is!) but the next year and thereafter with the cheaper DID chain?

anyway, having tightened a few decomp springs (try 20-30) in recent times i can tell that the OEM spring is too weak, that the decomp weight can flop around. that will explain the absolute battering the stop bolt has taken?

the golden rule with the decomp spring is that the long tail must point in the same direction on a parallel plain to the tail that sub-divides across the centre. it's about another 90 degrees of tension but is also 33% as well.

regards

Taffy

Taffy said:

i was doing a '04 650 yesterday and the camchain tension is completely used up! it's fully open. the chain, an IWIS is like new still. i suspect the chain has been rattling around. what i could do with is an old style tensioner with the blob on the end right now.....

i also checked and the auto decomp has been smacking hell out of the tiny bolt, it's almost 'D' in section yet it still hasn't broken - miraculouosly!!!! a floppy decomp makes a:clack! clack! clack! noise at very low revs as the blob bangs between the stop bolt and it's resting place.

the spring seems to be soft. now i don't do '04s everyday, infact it's only my 4th but interestingly, it's the third one with no tension adjustment left? now that has got to be a worry!

if not this, the only year that the quality IWIS chain was fitted (and it still is!) but the next year and thereafter with the cheaper DID chain?

anyway, having tightened a few decomp springs (try 20-30) in recent times i can tell that the OEM spring is too weak, that the decomp weight can flop around. that will explain the absolute battering the stop bolt has taken?

the golden rule with the decomp spring is that the long tail must point in the same direction on a parallel plain to the tail that sub-divides across the centre. it's about another 90 degrees of tension but is also 33% as well.

regards

Taffy

Click to expand...

Hi Taffy,

My idea of the decomp spring is to make sure the arm closed for start up, after that the centrifugal force keeps it out against the stop bolt, so if you have a decomp arm ratterling about it's either the spring is to strong and it wonts to pull the arm back all the time, or the rpm at idle is to low.
The weaker the spring, easier it is for the decomp arm to remain out against the stop at low rpm, or am I barking up the wrong tree here.

Regards

Sparks.

RE: Re: no tensioner left - floppy decomp

well it needs to be strong enough to act as a decomp firstly. so it needs to stay in close to the cam while the engine is turning over. that way you get the full decomp and she kicks like a 2T. that i've been acheiving.

i think the point you're making is that it's at that violently low revs where the buike wants to nearly stall and at times like that the decomp weight is like a rag doll! so the point here is about 'too low idle setting' or 'lugging the engine in a tall gear at low revs'?

the idea to me is that as the weight flies out, the spring should be strong enough to slow down it's speeding up towards that little M5 allen screwhead. there is a certain point at which it should fly outwards and that is after it has started and the engine isn't oscillating. so it flies out once - and stays there! the cam chain is an altogether more alarming worry.

manxberg had the side of the hole for the front chain guide bolt break out. basically, the cylinder head needed skimming due to it being run w/o coolant extensively. i had it skimmed and when i re-fitted everything there was no adjuctment left on the camchain tensioner at all. it was 'ok' so i started it iup in a donor frame and ran it up. it was fine after 10 minutes and i was happy. stopped it, stripped it out of the donor frame, tappets done and checked the tensioner....

nothing at all left and i know that the bike would have grabbed a few more clicks during it's first hours so this wasn't good.

luckily, keiran needed a month to collect the engine and in the meantime i managed to swop his tensioner for an old fashioned one with the 'blob' on the end. keiran then picked it up.

6-8 hours later the bolt that holds the drive side chain guide in broke out of it's hole in the casting. the bolt went in the camchain, snapped chain, valves and piston etc etc. husaberg drilled and tapped a hole (M6 thread) about 3mm from the edge of a dropaway in the case and the side had broken out. the only possible explanation was that the chain was rattling like phuq on the drive but more especially the OVERRUN!

it was welded and therefore is now stronger but that isn't good is it?

regards

Taffy