06-BDR Cam belt change - figuring out how
UPDATE AFTER THE JOB DONE:
This job is not for the feint hearted and there is a risk of destroying your engine (bent valves). Proceed with caution.
Mark the belt with say Tippex and the sprocket under on each of inlet and exhaust sprockets, jackshaft sprocket and the Crank Sprocket (Crank Pulley having been removed). Then transpose those marks to the new belt and fit that in exactly the same place on each of the sprockets (easier said than done so persevere).
You can cut the belt to remove it, but I preferred to not cut it and use removal as practice for fitting the new one and I am glad I did.
it turns out the things to be removed or undone are:
REMOVED
Crank pulley, but NOT the Crank Sprocket to which the pulley is bolted with three bolts.
Water pump pulley; 4 bolts.
Alternator belt comes off with the above two.
UNDONE/RELEASED
Idler - one nut, which cannot be removed due to proximity to the space frame, likewise the idler cannot be removed, but pulling it forward on its thread (while giving it a spin to check its ball race(s)) moves the front lip away from the Crank Sprocket allowing the belt to be squidged out and the new one in.
Tensioner; release not remove, one lock nut, one tensioner nut . And when belt fitted don't forget to re-tension this; causes all sorts of extra grief (re-aligning TDC with a dial gauge etc) when I found the crank was spinning without moving the belt.
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It's not a simple REMOVE and replace because things are in the way. Even when removed how to present the new belt is an open question.
Just seems odd to me, a i u i everything is driven by the crankshaft going round. Indeed when I turn the crank pulley manually, indeed everything goes round, so the world is as it should be. However, I can't see the cam belt going round anything on the crank so magical connection is in play. My wild guess is this connection is made by means of the idler pulley, but that doesn't have any teeth... so basically clueless.
I hope all will become apparent when I remove the water pump pulley.
I'll add Nigel's diagram, which does show the cam belt going round the crank pulley even though I think it doesn't..
Speaking of which diagram that shows TDC markers on the jackshaft pulley and the crank pulley, I now know from a handwritten diagram from Geoff who built the car, that the two left, one TDC and two right marks on the crank pulley are not that at all. The first and left most mark is TDC, the following are degree marks for 3,10,18 and 20
As yet no one has deciphered Geoff's diagrams, one for the crank and one for the cam. Don't know which cam.
So far it seems remove:
alternator belt (loosen alternator)
water pump pulley (4 bolts)
and I have various pics to try to visualise:
Quote
Andrew is suggesting an old trick
There's a trick you might get away with using. Failsafe way to get the new belt aligned correctly. Depends on whether you are feeling confident to try ...[Basically turn the engine over by hand, cutting the old belt in half lengthwise with a Stanley knife or similar. Then you cut and remove the front half of the belt leaving the back half in place.Then you can wiggle the new belt onto the fronts of the pulleys and only when that's properly located, cut the back half of the old belt and remove it.
But I am not feeling confident and/or because I have a fear of sharp knives (which seems topical these days).
and now something I can have a go at:
QuoteAnd the dizzy jackshaft. Alternatively: Put tippex marks on each pulley and on the belt to match. Takes old belt off. Lay both belts out on the table and carefully transpose the tippex marks to the new belt. Then fit the new belt and make sure the marks march up.
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