Author Topic: Timing side bush.  (Read 743 times)

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teebee67

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Timing side bush.
« on: 12 September, 2018, 09:14:12 »
Just had an expensive rebuild on my A65 race engine. This included a new timing side bush (all bronze type) supplied to size from SRM. The bush was fitted in the case then honed to + .0015" clearance by a reputable car race engine specialist. The engine was run up to temperature (10 mins @ 2000 rpm) 5 or 6 times. I took it to 3 Sisters race circuit to run it in and did about 7 to 10 gentle miles before a non engine problem put a halt to it. I then took it to a dyno to complete the running in and final set up of carbs and ignition timing. The dyno man was just warming the engine up on the dyno when within 2 minutes at low revs it seized solid. Removed from dyno and on initial inspection found we could move the crank slightly to and fro and the pistons were moving. I have now stripped the engine and found that the timing side bush is seized onto the crank.
When removing the sump hardly any oil (about an egg cup full) came out yet when the engine was stripped there was plenty of oil getting everywhere and the new big end shells are perfect and no signs of oil starvation anywhere.
Any ideas on the lack of oil in the sump and reason for the seized bush would be very much appreciated.   

Editor

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Re: Timing side bush.
« Reply #1 on: 12 September, 2018, 12:16:54 »
I'm not an expert but 0.0015" clearance seems way too small to me. I had a Thunderbolt crank re-ground and new bush like you many years ago and the engine told me he would machine it with a clearance of 0.005" (from memory).
I would contact SRM and speak to Geoff. He will advise the correct clearance.

JulianS

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Re: Timing side bush.
« Reply #2 on: 12 September, 2018, 13:00:20 »
There should not be too much oil in the sump, the scavenge gears of the pump being larger capacity than the feed gears.

teebee67

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Re: Timing side bush.
« Reply #3 on: 12 September, 2018, 13:01:30 »
Thanks for the reply. it was Geoff at SRM that said .0015 to .002. I have seen .0015 on other forums  as well but cannot find anything in my workshop manual.

teebee67

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Re: Timing side bush.
« Reply #4 on: 12 September, 2018, 13:02:24 »
Cheers Julian, I was thinking (hoping) that might be the case.

Shedman

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Re: Timing side bush.
« Reply #5 on: 12 September, 2018, 14:50:37 »
Was the bush honed as a single case or was it set up with the drive side case and line honed? Any misalignment would cause tight spots and that may have been the cause of the seizure. Also did you check the correct alignment of the oil feed hole to the annular groove in the new bush as any misalignment would impede the oil flow to the bush. In my manual it gives the crank to bush clearance of 1 to 1.5 thou

Bess

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Re: Timing side bush.
« Reply #6 on: 12 September, 2018, 15:03:26 »
Hi,
     From the manual, the crankshaft timing side, when new is supplied 1.4985 - 1.4980", the bush is 1.5000 - 1.5005", making the tolerance of 0.0015" to 0.0025".

Best wishes...

Shedman

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Re: Timing side bush.
« Reply #7 on: 12 September, 2018, 15:16:40 »
Obviously differences in manuals my manual states 1.4995 - 1.4990 for the bush fitted so what i am now wondering is what actully is the recomended clearance

teebee67

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Re: Timing side bush.
« Reply #8 on: 12 September, 2018, 15:31:47 »
The bush was honed whilst in one case not line bored. I didn't fit it so unsure about oil hole alignment but I understand the big ends rely on oil through this bush  so surely they would be starved of oil if it wasn't lined up?
My manual is a Haynes manual and doesn't give clearances so thanks for the info from the manuals.
 

Bess

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Re: Timing side bush.
« Reply #9 on: 12 September, 2018, 16:02:17 »
Hi,
    I have BSA workshop sheet A5065 GD3, copy attached.

Best wishes...
« Last Edit: 12 September, 2018, 16:18:36 by Bess »

Shedman

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Re: Timing side bush.
« Reply #10 on: 12 September, 2018, 16:54:51 »
Here is a shot from my 1971 A65 manual GD3
I am wondering if bsa changed the tolerances later in production

teebee67

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Re: Timing side bush.
« Reply #11 on: 12 September, 2018, 17:11:58 »
Thanks for the info gents but, unless I am being even thicker than usual, I can't see where we get the clearance from - especially after a regrind.

Shedman

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Re: Timing side bush.
« Reply #12 on: 12 September, 2018, 17:30:15 »
Whatever the final ground diameter of the crankshaft journal is the bush internal finished diameter needs to be larger by 1.5 or 2.5 thou dependant on which manual you use. Thats where your clearance is from. The manuals dont give the clearance as a specific figure its a case of adding the clearance figure to the journal diameter figure to determine the internal diameter of the bush

Bess

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Re: Timing side bush.
« Reply #13 on: 12 September, 2018, 18:02:21 »
Hi Shedman,
                  Yours is A65 only, I agree it's probably the later OIF model. What is the first regrind diameter of the timing side from your 1971 manual?

Best wishes..

Shedman

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Re: Timing side bush.
« Reply #14 on: 12 September, 2018, 18:45:29 »
First regrind is given as1.4885" - 1.489"