The effects of poor cam timing......misfire

[Botus]

yes.... I watched the video you found, interesting viewing. I wonder how much is sprocket and guide wear rather than just the chain, I guess u will find out soon.

no one told me how you pull a chain through without the pistons and the valves arguing?

 

[om613]

Bikers or cyclists may know that a worn drive chain also wears the sprockets, as the effective pitch increases.

The same principle should apply, do you think?

 

[Arudge]

yes.... I watched the video you found, interesting viewing. I wonder how much is sprocket and guide wear rather than just the chain, I guess u will find out soon.

no one told me how you pull a chain through without the pistons and the valves arguing?

Sprocket and guide wear is something i'll be paying close attention to.

I think the crank is set at 20deg for setup because at 20deg all valves are closed or as near as dammit, therefor safe to rotate the crank and pull the chain through. we'll soon find out.

 

[Arudge]

Bikers or cyclists may know that a worn drive chain also wears the sprockets, as the effective pitch increases.

The same principle should apply, do you think?

In principle yes.........However.......

My triumph motorcycle has done 40,000miles, the chain is original as is the rear sprocket. The front sprocket was changed when i could hear the chain snagging, although the front sprocket was hardened it was trashed. The chain was OK, checked the stretch between a numbered amount of links and found no wear at all. The rear sprocket was soft but again, no measurable wear. New front sprocket fitted and all is well.

Steve stated that the 'pull through' method for changing the chain was standard MB practice, this suggests the crank sprocket is deemed fit for purpose because it can't be inspected, it's buried in the bowel of the engine. If the crank sprocket was vulnerable i'm sure the procedure would call for the front casings to be removed for sprocket inspection/replacement.

That's not to say that all MB's procedures are correct, filled for life transmissions are a case in point. I will be paying close attention with this cam chain change because i don't think it's quite as 'fitted for life' as we've been led to believe, but we'll soon find out.

 

[LostKiwi]

no one told me how you pull a chain through without the pistons and the valves arguing?

Its pretty simple.
You split the old chain at the master link.
Join the new chain to old one.
Wind the engine over by hand pulling the new chain in and the old one out.
Once at the join split the old chain from the new one and rejoin the two ends of the new one.
Reset the tensioner, check timing and all good (assuming sprockets are OK).

 

[star]

Its pretty simple.
You split the old chain at the master link.
Join the new chain to old one.
Wind the engine over by hand pulling the new chain in and the old one out.
Once at the join split the old chain from the new one and rejoin the two ends of the new one.
Reset the tensioner, check timing and all good (assuming sprockets are OK).

Not so easy on some engines as the piston will jam against an open valve. Either romove cams or hold chain agains cam sprockets and turn as one ( it will try and jump) or on certain engines you can hold the cam in a certain position where the crank can do a full revolution without jamming.

 

[Botus]

Not so easy on some engines as the piston will jam against an open valve. Either romove cams or hold chain agains cam sprockets and turn as one ( it will try and jump) or on certain engines you can hold the cam in a certain position where the crank can do a full revolution without jamming.

good point, getting too old... forgot take the cams out unless you rev to 20k pulling the chain round the valves should be pretty safe !!!

 

[Arudge]

I've changed the cam chain.

There's good news, and there's bad news.

The good news.
The misfire has gone, the hunting has gone, the idle is now rock stable at 600rpm and moving off from a standstill is brisk. I can't feel the engine running at idle and the whole driving experience feels more refined.


The findings.
The cam chain adjuster was at the end of it's travel, the chain is approx 1200mm long and had stretched 7mm. Appalling i think, for 107,000 miles.

The new chain timed up at 23deg for both inlet and exhaust. The book calls for 20deg with a limit of 30deg for the inlet and 35deg for the exhaust. The 3deg error could be wear in the right chain guide, manufacturing tolerance in the chain or a combination of both. Either way i was pleased with the result.

The bad news.
I dropped the chain, not once but three times into the sump and there was some very strange goings on with the chain guides. The result of which, it took me a whole 13 hours start to finish, including stripping out the super charger, the cams and the upper front casings to get a better look of the lower crank sprocket.

The riveting tool i bought was worse than useless.

I'll go into more detail later.........

 

[LostKiwi]

Well done Andy!

 

[Paul Goff]

Bikers or cyclists may know that a worn drive chain also wears the sprockets, as the effective pitch increases.

The same principle should apply, do you think?

Agreed, I change the chain at about 1000 miles, the rear sprockets with every second chain and the front chain wheels every forth chain. It is all working in awful conditions though, particularly in a muddy, gritty Devon winter!

 

[Arudge]

Where it all went horribly wrong.

I set the crank at 20deg and removed the tensioner, as per MB procedure. I noted that most of the valves were closed but one pair on both inlet and exhaust were slightly open. I removed a link from the chain and a few moments later the exhaust cam kicked round a little, launching that end of the chain off the sprocket and it was drawn into the cavity by it's own weight. Oh joy.

Fortunately, the chain was bunched up and i was able to fish it out with reasonable ease, i managed to do that twice.

I attached the new chain to the old and very carefully wound it round by hand. Stop. That's very definitely a valve so i removed the cams. As i got to the end of the new chain it slipped from my grasp as i was about to secure it with wire. This time the end of the chain disappeared from sight and into the sump. I don't believe it.

I stripped off as much from the front of the engine as i could, i couldn't remove the front pulley because i hadn't the special tools.

I removed the cam chain completely and fished a wire around the crank cam sprocket, which is a long way down!! Pulled the chain through again, assembled the cams and........i'm two inches short on the chain, what in Gods name is going on? I surmised that there is a boss under the crank sprocket and i've pulled the chain around the sprocket, and the boss, which is clearly no good. All apart again.

I managed to attach a fragment of one of those Neodymium 'super magnets' to the old chain, bonded and wired on. After a bit buggering about i managed to get it onto the top of the sprocket and wind it round. We're back in the game.

All back together, and.........i'm two links short.......WHAT THE !!!! Arghhhhh. All apart again.

I'm happy the chain is on the crank sprocket correctly. My attention turns to the cam chain guides. The're loose but they can't be removed, the're secured at the base where i can't get to. I jiggle them both around a bit and reassemble everything. Something has moved because now i'm only one link away, not two. All apart again.

In a fit of frustration i 'G' clamped the cam chain to the inlet cam sprocket and heave on the crank pulley, the cam can't move because it's pegged in place.

All back together again and........i've got half a link of slack!!, .

I honestly have no idea what's going on with the guides, they clearly don't locate positively and have a big influence on chain length, hopefully somebody with more experience can enlighten me. There's certainly nothing on any of the you tube clips i've watched.

Fitted the master link, reset and re-fitted the chain tensioner. Removed the cam locking pins and cranked the engine by hand. This is important because hand cranking allows the tensioner the take out any slack, you can hear the tensioner click a couple of times then you know it's safe to start. If you don't bother or forget, the engine will be too fast for the tensioner and it WILL skip a tooth or two before the tensioner kicks in.

The result was very rewarding, even if the experience was hard earned.

Apologies for such a long post but i thought it was worth sharing, even if it was such a disaster, the end result was sweet.

 

[Arudge]

Well done Andy!

Cheers

 

[LostKiwi]

I think reading of your trials and tribulations it would have resembled a Molotov cocktail long before I'd finished if I'd been doing it!

 

[Arudge]

I think reading of your trials and tribulations it would have resembled a Molotov cocktail long before I'd finished if I'd been doing it!

My mate, at work said, if it had been his he'd have pushed it into the canal, which was all of 10' foot away!

 

[LostKiwi]

My mate, at work said, if it had been his he'd have pushed it into the canal, which was all of 10' foot away!

Wouldn't want to block it and flood the house as well!

 

[Arudge]

I thought Steve Avantgarde may have chimed in, but he probably still hasn't recovered from the last bout of laughter!!

 

[ajlsl600]

The problem i had was that i couldn't re time the cam because the locating holes didn't line up, just like the video. But i couldn't believe the chain could have stretched that much, but it has.

Star has indicated that he's done a cam chain change and got rid of a mis fire problem, and that's enough for me to go in and do the job.

You know more than most just how many hours have been poured into this little car, you've helped out yourself. With all the work done on the induction system, the throttle body, the supercharger, the vacuum pump and it's associated vacuum leaks, new MAF and new plugs. The oil we've cleaned out of the inlet manifold and intercooler. We've even pulled the engine ECU apart and cleaned out both oil and the dreaded Verdi gries from the pins. Everything we did appeared to make some improvement but we never seemed to cure the mis fire, never found the root cause.

If.....just if...the cam chain is the root cause of the mis fire due to poor cam timing, then at the next GTG i'll buy you all a beer.

Cam chain and cam chain breaker/riveter have been ordered.

Fingers crossed.

just out of interest from where did you order your riveter...

 

[ajlsl600]

There is a special tool for rejoining the chain. Once you have done it, you have the confidence to do it again and again. The tools for doing are so good you can't actually tell the master link from the normal one.

do you know an ecconomic supply for that chain riviter,peener. or a drawing so one could make it i need to do one of my a class diesels

 

[Arudge]

I had mine from eBay, it was rubbish but I managed to get it to work in the end.

I'll look it up later when I get home.

 

[ajlsl600]

just seen one on flea bay 79 quid . wont be best quality , but will do and any rubbish bits i can make myself unless someone knows of one for less ?