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Bodiam Posted - 05 Sep 2020 : 07:39:31
Just completed a full engine, gearbox and overdrive overhaul, inc new clutch. Gearbox and overdrive were both in good shape, but renewed a cone clutch in the overdrive and renewed gearbox bearings as a precaution.

However, I have a couple of problems, which may be connected, on which I would appreciate some help. The change down from 4th to 3rd gear crunches almost every time, no matter how careful I am, also the engine revs drop markedly when I dip the clutch at a standstill - I am sure the engine would stall had I not set a fast tickover while running in.

The clutch feels moderately heavy, but first and reverse gears engage cleanly at a standstill, so the clutch seems to be clearing ok, though I may overhaul the slave and master cylinders to see if it helps.

Crankshaft end float is within spec, but thrust washers were replaced anyway when the engine was overhauled.

Before all this work was done, the gearbox functioned well, though I did notice the starter struggled to turn the engine over if I dipped the clutch, but spun over normally if I engaged the clutch. I rather thought this may have pointed to thrust washer wear, but they were ok.

I’d appreciate any thoughts from more experienced owners out there - I am wondering whether the new clutch may be at fault, especially as the revs drop so much when I depress the clutch at tickover and I can’t think of anything else that might cause that to happen, given that the crank end float is ok.

Thank you in advance for any guidance you can give me, I’m not getting much enjoyment out of the car at the moment!

Kind regards, John
10   L A T E S T    R E P L I E S    (Newest First)
bigt80 Posted - 17 Oct 2020 : 20:56:17
Yes, thanks John for your update - maybe it will improve taking it carefully during the running in process. Cheers! G
Bodiam Posted - 11 Oct 2020 : 14:07:32
Hi, Richard,

Thanks for the heads up - yes, using straight 30 engine oil (learned my lesson on a TR6 a while ago!)

Kind regards, John
rapier123 Posted - 10 Oct 2020 : 19:25:10
Crunching gears can be down to using the wrong oil, make sure your using engine oil and not gear oil.
Bodiam Posted - 09 Oct 2020 : 10:40:57
Hi, Glen and Jim,

Thank you both for your comments.

The clutch cover, disc and carbon release bearing were all renewed while the box was out but I take the point about renewing the clutch hydraulics - not expensive so worth a try.

For now, I’m taking it gently and double declutching to (usually) get a clean change from top to 3rd until I’ve run the engine in. Then it’s decision time again.

Thanks again for your interest.

jimlagos Posted - 04 Oct 2020 : 10:50:16
I once had the same problem where depressing the clutch slowed the engine. Eventually the most awful screeching happened when I depressed the clutch! Turned out that it was the carbon release bearing had virtually gone and also scrapped the clutch cover!

bigt80 Posted - 04 Oct 2020 : 10:29:33
I am not a mechanic or expert, but I believe a small amount of wear in M/cyl &/or slave can translate into clutch not operating fully. If you have gone to trouble of refurbishing a complete g'box, I would say it is worth getting new or at least reconditioning both of those - it may just ease your 4th to 3rd change issue?

Normally a big dip in engine revs on tickover on engaging clutch can point to worn thrust brg or a lot of end float, but I know from experience that, that can still happen when all has been renewed: just seems to be a trait of the carbon brg set up. I learnt early on in my ownership of Rapier's not to keep it in gear/ride the clutch in traffic and get into neutral as soon as possible in order to reduce wear on the bearing . G
Bodiam Posted - 06 Sep 2020 : 10:10:22
Hi, Mike,

Thank you for that - apart from the gear crunching issue, I’m struggling to understand why the engine revs fall so markedly when pressing the clutch on tickover, I guess whatever is causing that is connected with the engine struggling to turn over on the starter if the clutch is depressed while it spins over normally if it isn’t.

I had thought that maybe the crank thrust washers were worn and causing this, but they are fine and end float is within spec.

I am beginning to think the spigot bearing may be at the bottom of this, or maybe there are two separate issues, but either way I can see the gearbox coming out again....

Many thanks again,

Kind regards, John
Sunbeam-mike Posted - 06 Sep 2020 : 09:54:33

many years ago I remember the spigot bearing was badly damaged when the bellhousing/engine was re-assembled.

These made t seem that the clutch did not dis-engage properly.

Just a thought...

I ought to mention that this was not on a Rapier, though.

Mike Hooper
Bodiam Posted - 05 Sep 2020 : 12:00:16
Hi, Peter,

Thank you for your suggestions, I will follow them up at the first opportunity.

The spigot bearing was not renewed, but since posting I have found one issue which needs to be dealt with - I noticed some advice you gave in an earlier thread and checked that the slave cylinder has been fitted the correct side of the bell housing. This is correct, but the bleed nipple is at the bottom and I understand this is incorrect. The cylinder has started weeping, so I think I will renew this with the bleed nipple in the correct position and see if that takes us anywhere.

Thank you for your interest,

Kind regards, John

John D
pruyter Posted - 05 Sep 2020 : 11:22:01
There could of course be something wrong with the new clutch, but that is difficult to establish with the clutch installed. I would inspect the clutch by using an inspection camera and in order to do that you have to remove the metal shield between the engine and the gearbox.
If you find somebody to press on the clutch pedal you are able to see what happens when you use the camera. In stead of the camera you could also use an inspection light.
Did you by any chance renew the spigot bearing?
The fact that you only have crunching gears while selecting 3th of 4th gear does me supect that something is wrong in the gearbox (you have overhauled it and possible some mistake has been made...). Normally, if the clutch is at fault, one should expect problems while engaging 1th gear or reverse



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