Jackshaft and bearings re low oil pressure

[Paul Kelley]

In the context of low oil pressure, especially at idle, am I right in thinking that the jackshaft front bearing, in particular, is a prime suspect to check for wear? If so, how easy is it to replace? Likewise the back bearing? Should any other jackshaft-related bearings, e.g. the water pump, also be replaced? As for the shaft itself, and front and rear gears, are the new replacement parts known to be of good quality? Given its critical multiple function, quality is clearly a major concern. Sorry, quite a few questions together here! As always, your knowledge and thoughts much appreciated. Thanks, Paul.

[NeilR]

I had an issue with the jackshaft front bearing being badley worn & scored on an engine I rebuilt for my brother.

Low oil pressure was not a particular issue, but the wear in the jackshaft bearing starved the RH camshaft of oil and
seemed to cause premature wear of the followers on that head.

Had it bored out & sleeved, quite tricky to find someone who do it because of the small size of rear bearing to allow
the line boring tool to fit. Did eventually find somebody though - Coventry Classic Engines.

A new jackshaft was supplied to the engineering company and the front sleeve machined to suit. Solved the problem of
oil supply to the camshaft.

Can't comment on the quality of the replacement jackshaft though as the car was sold.

In your case I would suspect the crank, but have you fitted a new pump ?. I had an issue with low hot idle oil pressure (10-15 psi) which turned
out to be the County oil pump which had done about 20k miles. A new pump - again a County solved the issue (35 psi at idle when hot).

Neil.

[Paul Kelley]

Hi Neil

Thanks for the reply, thought it would be tricky to do. Was the wear on the front bearing easy to spot? I should have said, I fitted the LD Parts replacement upgrade to the existing pump and no discernible difference. Yes, I think the crank and lower end bearings will need replacing.

[NeilR]

The scoring was very obvious. No idea how it got like that, must have been some swarf or something like that from previous maching.
There was excess running clearance with the new jackshaft, you just feel slight play moving the shaft side to side - orginal shaft was scrap as very badly scored.

I still think it's worth sporting £45 on a complete new pump just to prove it. As it solved my issue which sounds identical to yours.

We know the story with pattern parts don't we - aftermarket internals to an original Oil Pump housing, which maybe worn as well.

But that's just my opinion.

Neil.

[Paul Kelley]

Well, there's only the County pump available new, so will get a Robsport one with their adapted/correct spring and see what that does. Worth a try and will need a new pump regardless.

[flying farmer]

Casting sand plays havoc with jackshaft bearings, the engine in my 246bhp stag was fitted with a new jackshaft some time before I bought it and the shaft was still good although the block had several grooves worn in it. It had mk2 heads fitted to a MK1 block and I reckon there was a good chance the cam bearings and buckets of the original heads were trashed by sand. I got loads of extra sand out of the oilways before I rebuilt it, but the side to side play was still acceptable (from memory about 2-3 thou)

My P reg stag that suffered seizure of the jackshaft front bearing due to water pump failure did need the front bearing sleeving.

With a new shaft fitted and the jackshaft bore honed there was about 8 thou clearance from memory which I regarded as too large. A local engineering firm fitted a phosphor bronze sleeve which was pegged in position to stop it turning and closing off the oil passages. That engine only had about 30psi hot oil pressure before it went bang, but the crank was quite worn as well.

Neil

[Paul Kelley]

Thanks farmer Neil (two Neils on this thread!). The diagnosis so far is pointing to worn mains but we'll also check the jackshaft and related bearings. The mechanic I use for the 'heavy lifting' stuff has a fantastic workshop - he makes his own highly modified cars and american trucks - so he may be able to fashion a phosphor bronze sleeve along the lines you suggest, if needed. We're now working on the basis that it's an engine out, crank regrind and toughen job, so best to sort pistons, bores, and jackshaft at the same time. The cylinder heads, cams and valves and timing chains/sprockets are all good as done recently. Hey ho, will have a rebuilt engine by the end of this! Anything else you reckon I should check, replace etc whilst digging deep?
Cheers, Paul