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BDR Cam belt change - figuring out how

anthony1956

Entry posted by anthony1956 in BDR MATTERS

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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. 

==================================================================================================================================================

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..

IMG_3103.thumb.webp.ec91f657365e1943840e43d73c76080c.webp

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:

Idler.webp

IMG_2920.webp

IMG_2923.webp

IMG_2934.webp

IMG_3014.webp

IMG_3050.webp

IMG_3055.webp

IMG_3056.webp

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:

Quote

And 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.

 

Edited by anthonym
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Nigel Blandin

That drawing is a BDP race motor Anthony. It was just to show the idea of timing marks down on the crank pulley.

 

Our motors have the main toothed belt driving the cams and jackshaft from a toothed crank pulley. This pulley is behind the larger V belt pulley which separately drives the water pump and alternator. 
The idler pulley, lower right, is just to keep the toothed belt in contact with the crank pulley for more of it’s circumference.

Sorry for any confusion 


 

 

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anthony1956

no problem, thanks. 

I awoke this morning remembering the official emissions test is over-due so I think I should do that first.

Edited by anthonym
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Nigel Blandin

I asked Sherwood motors about the timing marks on the cam pulleys with your photo and got this response back;

 

Paul is on annual leave this week so I've had a word with our senior engine builder.  He has said that the marks on the pulley could've been put there by anyone and doesn't necessarily mean anything.  Your friend needs to use a timing disc and DTI to set the timing.
 
I hope this helps, if not please let us know and I'll try and find some further information to help you.
 
Many thanks
 
Best Regards
Louise
Louise Lorton
Office Manager
AIorK4wkWsL7m44Mu5XizUePH3j6eo8mZHMSXYgn9Dsn3KYmNbRKNxzBAnfA9Q-PdzQPct_blVPctWw
Sherwood Engines Ltd
Unit 5 Faraday Road Business Park
Littleport
CB6 1PE
01353 864888
 

 


 

 

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anthony1956

DTI? Guess that might be a dial gauge, which is what we did in the absence of any reliable marks.

As to a disk if he means for the degrees BTDC we worked out how many mm of arc i 6 degrees and went for that, by eye. She goes like a rocket, wonderful.

Sadly I now have to change the belt!

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anthony1956

Ans so a bit more as I have now removed the water pump pulley and for the first time I can see the belt does indeed go around the crank pulley, which is a much much deeper affair than it at first appears to be. I also spy what looks like a timing mark to match TDC on the crank pulley, which is the edge of the idler, lined up perfectly to the TDC mark; bearing in mind in all my previous mentions I thought the TDC mark was the central one of five whereas it is the left most. 

What I am trying to do here is use getting the old belt off as practice for putting the new belt on. 

Right now it looks like magic is required.

Pics following:

 

IMG_3286.webp

Above water pump pulley: hold one bolt while undoing another...no need to release the alternator at this point as it drops out.

IMG_3287.webp

My first sight of the crank pulley cam belt teeth holders

IMG_3292.webp

Spotted TDC mark on crank pulley exactly matches edge of idler, this is having set No 1 TDC with a dial-gauge. It may look slightly off, it's not when viewed straight.

IMG_3293.webp

So how on this Earth do I get that belt off or a new one on? There is no space at all behind the crank pulley.

IMG_3294.webp

Even with the idler off how to get the belt in between the crank pulley and the Jackshaft pulley?

I may need to jack her up and see what space is down under.

What I REALLY do NOT want to have to do is lock the crank to take something off because I don't have the tool.

 

Edited by anthonym
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Jonathan Kay
42 minutes ago, anthonym said:

 

DTI? Guess that might be a dial gauge, which is what we did in the absence of any reliable marks.

"Dial Test Indicator", same as a gauge.

Jonathan

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anthony1956

very slightly Heath Robinson (very early pic, before anyone comments)

IMG_3222.webp

Edited by anthonym
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anthony1956

so I found the answer I was looking for from a 2012 picture, we have botha Crank Pulley AND a Crank Sprocket bolted together and the Crank Pulley easily unbolts to expose the Crank Sprocket

 

20120725_150432.webp

Edited by anthonym
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anthony1956

ok so I thought the idler nut was F tight and beyond me, but using a 5/8 spanner with a lever through the other end broke what I think looks like old Loctite. Belt now off.

Here are the pics including transferring the white marks on the old belt to the new, ready to match to the marks also on the sprockets. Marking the crank wasn't possible but the Jackshaft is so we will hacve to see if I get it on the "right tooth" as they say.

 

Idler before nut undoneIMG_3319.webp

 

Idler after nut undone - makes enough space to remove the belt forwards. Note not enough room to remove the nut and no chance to remove the idler.IMG_3320.webp

Celebratory pic old belt removed, shows marks for transfer

IMG_3321.webp

Matching marks from old belt to new

 

IMG_3323.webp

 

Edited by anthonym
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anthony1956

Right then, old belt off, new belt on.

Fubar:  not tensioning the tensioner before turning the crank. So I turned the crank and nothing else turned much. Back to first principles with the dial gauge. I THINK cam sprockets, Jackshaft and crank are all now at TDC No 1 compression stroke.

And so, the UN Fubar process, belt and braces being applied:

Turned the engine with only no 1 plug installed, compression on the current stroke.
Dial gauge at TDC 
Cam sprocket alignment marks are aligned
Jackshaft - Dizzy Rotor is pointing at No 1 - even if now approximately.
Crank Sprocket TDC (?) mark is in the same place as before.
No 1 cam both valves closed, exhaust will open next
Idler nut tightened.
Tensioner tension nut tightened and lock nut thereafter.

I thought cam belt was too tight but after 720 deg turns, twice it twists nicely to 90 deg on the long run.
I gather if I had bent a valve I would not be able to complete a 360 turn of the crank.

Stopped for tea to consider if there is anything else before attempting to start her.

Oh yes - REFIT THE ALTERNATOR/WATER PUMP BELT AND THE CRANK PULLEY, REFIT WATER PUMP PULLEY.
not that I really need those to see if it starts.

 

 

 

 

 

Edited by anthonym
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