StratfordShark

I'm in middle of TB project and changing cam gears.

The crank is locked 45 BTDC, and before I started the job I used Porken's 32vR to check timing at TDC with old belt on and it was correct, -2 RHS, 0 LHS.

I marked the gears with paint at the 45 position aligned with the notch on rear (3 teeth over from notch at rear of gear as you would expect). I also had the little bolts from the 32vR in the slots so I could mark where they were.

I've just unbolted the RHS 1-4 gear using 30mm on hex washer and socket on 17mm cam bolt. The cam didn't slip and the gear came off fine.

As soon as I put the 30mm on the LHS gear to counter hold that cam snapped clockwise about 5 teeth! I loosened the bolt and marked where the gear now aligned with the rear cam notch. I thought it wouldn't move with the little bolts snug in the slots, but I clearly have not understood quite how the gear, "spider" and cam work to stay in step.

What is correct procedure to get the timing roughly right so that I can refine with 32vR later when new belt on? Do I put new LHS gear on in position to match where the old one slipped to i.e. transfer the paint mark from old gear to new and align that mark with the rear notch before I bolt it down, and then pull that gear anticlockwise back to original 45 BTDC mark before the cam snapped as I put the new belt on, or follow another method?

Thanks a lot! I knew changing the gears would be one of the tricky bits...

mike77

I had a similar problem with the left hand cam when I did mine. Locked at 45 the left cam just kept jumping forward. I had a lot of trouble keeping it in position and getting the new belt on. I rotated my cam clockwise back to position but am now wondering if that was correct or not. I also read that removing spark plugs makes the engine easier to rotate. I wonder if it may also make it easier to hold the position of the cam?

Good luck

ammonman

Turn the cam clockwise 360 degrees back to the correct position (3 teeth before TDC) and re-install the belt. With the crank locked at -45 degrees there is no danger of the valves hitting the pistons. I usually have to use a wrench on the 30mm hex washer to hold that cam in the correct position to get the belt back on correctly.

Mike

StratfordShark

Thanks Mike. Can you confirm at what position I should install the new gear? Should I put in on in the same (slipped) position where the old gear ended up b I've marked the tooth in line with rear notch in position it stopped.

depami

Isn't the spider keyed tight and the gear keyed loose thus allowing only one possible fit?

Put the parts on and tighten with three bolts centered (or in the previous position) in slots then turn cam clockwise to three teeth before notch and install belt.

Proceed with belt install and 32VR adjustments.

wpgshark

2 people for the actual belt install makes it go more smoothly. I had my son hold the left cam in place.

Remember to run the engine around manually for 2 revolutions to check that the marks line up again.

Good luck

StratfordShark

Yes it is arranged like that with some leeway allowed on cam gear as key is wider.

I'll follow your suggestion with bolts centred and then turned clockwise (any reason can't go anticlockwise with no belt on?), and see where things are once belt is installed.

Thanks

fraggle

Moving anticlockwise isn't ideal for the cam chain tensioners. That said, I've done it a bunch of times in situations like this, where the valve springs push the cam out of position. Someone is going to hate on me for it, and I might not risk it on someone else's car, but I wouldn't hesitate to do it again because getting the belt on when you're by yourself can be a pain in the ***.

Bertrand Daoust

+1.
I've done that too!

What is correct procedure to get the timing roughly right so that I can refine with 32vR later when new belt on? Do I put new LHS gear on in position to match where the old one slipped to i.e. transfer the paint mark from old gear to new and align that mark with the rear notch before I bolt it down, and then pull that gear anticlockwise back to original 45 BTDC mark before the cam snapped as I put the new belt on?

Yes.
That's what I would do.
Actually, that's exactly what I did last year when I did mine.
I also used the 32vR (thanks Luc!) to refine the timing.
Everything's perfect now.

Good luck.

WallyP

If you should miss by one tooth, you can make a hump in the belt with the slack and walk the hump around the gear to move one tooth at a time. I use spring clamps to hold the belt on the gear.

StratfordShark

Thanks Wally - I picked up set of spring clips just in case for this job

FredR

Adrian,

This is perfectly normal and nothing to worry about period- it is the very reason you lock the crankshaft at the 45 position. The three little bolts hold the timing when the belt is on but with out the belt it only takes very little [often no] displacement and that cam bank goes twang against the valve spings.

Do not worry about cam timing at this stage- just mount the new cam wheel roughly in the middle of the slot and torque up the bolt to 47 ft lbs. When you are good a ready to fit the belt, Note where the white mark is on the old wheel that I advised you to make and that will index your position for fitting the belt over the cam.

When the time comes to fit the belt rotate the cam using the big washer to drive the cam wheel forwards [clockwise only] until you get it to the point where it is more or less aligned with the notch on the casing.

You feed the belt starting from the 1/4 bank with the tensioner totally slackened off with the refit being completed as you slip the belt over the 5/8 cam wheel. It is a tight fit to get the belt back on and you will need to take up all the slack in the belt train to get the new belt over the cam wheel. Remember the new belt has not streched yet. Once the belt is back on correctly aligned and you have tensioned the belt, then you can go about setting the valve timing correctly.

Remember with a new belt you have to allow for the impending stretch which requires a couple of degrees of advance on the 1/4 bank if my memory serves me correctly. Thus when setting, 5/8 is set at zero, 1/4 is set plus 2, after you spin the engine a few turns on the starter it should read zero zero and after the belt has settled [about 1k miles] it should then read minus 2 on 1/4 and zero on 5/8 if you want stock timing.

I trust someone will pick me up if memory is wonky. I did not allow for the belt stretch when I set mine and when settled 1/4 was retarded two more degrees than I wanted.

Regards

Fred

StratfordShark

Thanks Fred that's very reassuring and old gears were all marked up at 45.

Only query on your post is I thought belt was string first over crank then up to 5-8 via oil pump, other way to your order which finishes at 5-8?

FredR

Adrian,

Apologies I believe you are right on that one- the trick is to string from the crank cog, to the oil pump cog then the 5/8 wheel and then keep tension in the belt with a spanner over the 30mm washer pushing counter clockwise to stop the cam cog plunging forwards again- extra pair of hands useful but not necessary- that will leave you free to engage the belt over the 1/4 wheel- it is a bit tight but I managed to do it first attempt.

Rgds

Fred

StratfordShark

OK thanks Fred - I'm sure I'll get the hang of it after a few goes!