what's the trick for re fitting cam sprockets?

[jono]

I'm having problems with this, having fitted a new head gasket.

My engine has been timed using verniers pulleys. Before I removed the head I lined everything up with cam lobes facing inwards on nr 4 and the engine set to TDC. I marked the crank pulley and timing case and also the cam sprockets level with the top of the head.

When I come to put it all back together again I find that the chain seems too slack between the exhaust pulley and crank pulley and I can't get the chain over the inlet pulley without upsetting the timing marks. I've got the tensioner backed right off and removed from the timing case.

I don't think there is anything fundamentally wrong it's just a matter of technique I think - first time I've done this job.

It's not made that much easier by the pulleys which are a bit more chunky that the std ones and the cap screws heads also make them a bit harder to manipulate.

Any suggestions on a simple technique for a newby to this, such as myself

Jon

[david.g.chapman]

Assuming the vernier pulleys have not been adjusted since dismantled, it should be possible to get back to where you were without too much trouble.

Make sure that the chain tensioner is backed off first of all - screwed out.

I would fit the exhaust sprocket first, making sure the chain runs tight from the crank sprocket. You might need to tweak the exhaust cam position very slightly - I used a torx fitting at the back of my cams for this.

Then, the inlet sprocket can be fitted. Pull the chain up as far as it will go, so the chain is tight everywhere. The jackshaft will rotate, so you want the rotor arm to be in a convenient position when the chain is tight, and pointing to the no.1 plug. Do this once or twice until you are happy.

Now fit the inlet sprocket. Get it onto the camshaft dowel and quickly check the timing marks on both sprockets. If one is slightly up and the other slightly down (1 or 2 mm) you might be there. You might also need to tweak the inlet cam position as well to get the sprocket on - be patient.

Now tighten up the chain tensioner and check all the timing marks at tdc. If it looks like 1 tooth out - marks 4mm up and 4mm down, then start again with the exhaust cam repositioned. Stay chilled

Good Luck

Dave Chapman.

[billwill]

The tensioner should be fully slackened, even with its piston taken out if necessary.

As David says, put the exhaust sprocket on first ensuring first that the engine is at TDC, and the chain is taut from crankshaft to exhaust sprocket, check that the sprocket timing mark is close to the horizontal in facing position. Keep tension on the chain (with your fingers of your third hand Or a bit of electric wire or an elastic band ) to stop it falling off the crankshaft sprocket at the bottom. Insert exhaust-sprocket's washer and bolt and do up finger tight taking extreme care that you do not drop them into the sump! I generally hold the bolt in a socket spanner with an extension bar, but no T-bar to insert the washer and bolt.

Fit the inlet sprocket into the chain to find the correct matching links in the chain, offer it up to the camshaft each time until you see that the timing mark will be horizontal facing the exhaust mark.

If the tensioner is slack enough you can now slip the inlet sprocket over its camshaft and wiggle it until the dowel goes in. Look down inside to check that the chain looks OK around the layshaft. Put the washer & bolt of inlet sprocket in and do up finger tight.

Gently increase pressure using the chain tensioner, checking that everything is still in the right place, until the top span of the chain flexes just a half inch as shown in the manual. The camshafts and layshaft may move slightly.

Now check that the timing marks line up just exactly like the digital photo you took before you removed them. You did take that photo didn't you ? Remember that they can only line up to within one sprocket tooth distance anyway.

In many cases you will now cuss loudly, slacken off the tensioner and do the inlet sprocket all over again moved one tooth relative to the chain. (been there done that got the T-shirt).

Finally sure that the timing is as exact as can be, tighten the sprocket bolts to the correct torque. (put the engine in gear and handbrake on to stop the camshafts rotating).

Now you have no real idea which tooth of the layshaft engaged the chain, so take out the distributor and refit it and re-time as per the manual It may need to be in a different tooth of its helical gear.

[jono]

Thanks for the comments chaps.

..I have no distributor so that's one less thing to worry about

As said, it's made more tricky by the vernier pulleys which are much thicker than the originals - . It would have been a lot better if the chain slipper had been adjustable also so that the chain could have been pulled up with the exhaust pulley already in place. But then that would have been no fun (or should that be 'frustration'), and so very 'un Lotus'

..will try again tonight and report back with an update

Jon

[billwill]

My topic on Clay Test has photos that may help.
I have the adjustable sprockets too.

lotus-twincam-f39/clay-test-checking-clearance-between-valves-pistons-t26441.html?hilit=clay%20test

[jono]

Thanks chaps,

Last night I eventually cracked it! It seems to have taken me ages and many cycles of 'take off and start again'.

I'm not sure what my problem was (save, of course, for competency ) but it all seemed to fall into place when I decided to move the chain position on the crank sprocket and pull it back up, perhaps there was a kinked link or something?

Anyway all now lines up and I have turned the engine a few times and there are no worrying noises.

Hopefully I should have it all fired back up at the weekend and here's hoping the oil in water problem is now solved

Jon