3 Bearing Engine

[Henry Harris]

Today I've been scavenging bits from the Rolt 3 bearing engine that I broke during a 750MC 6 hour Relay Race in the early 90's.
I'm planning to use as many of the Rolt bits as possible in a good crankcase with a new crankshaft. 
Some time ago there was an article on the Speedex web site about adjusting the centre main bearing. 
I'd like to see it again but can't find it.
Is it still online?

   

[Tony Press]

My memory is the A7CA website group were working on recovering it.

[Jamie]

Good morning.

I had the same question recently. If you could send me your e-mail address, I shall forward you the instructions. The chap who did the original article e-mailed me a copy.

Regards,

Jamie.

[Chris KC]

Henry,

Stuart used to make a new c/m upper housing (with added machining allowance), and mill 15 thou off the top face of the lower housing; then, with the block firmly tightened in place, bolt them in the case with correct torque and line bore the assembly (actually he used a massive reamer in a lathe). The centre main housing is fixed with long bolts instead of the Austin studs so as to isolate it from the block. Done like this all three bearings are in line and there is no need for 'adjustment' - fit and forget. If your crankcase is not 'perforated' I would re-use it; otherwise I would suggest to follow the same method with a new case. I can provide comprehensive detail if it is helpful.

May I ask what are your plans for the 'new shaft'?

Regards
Chris

[Henry Harris]

I will dismantle and check the Rolt crankcase but suspect that it will be too distorted after the crank breaking.
The original oil pump system with a modified Austin pump was not satisfactory. When I was first racing it was necessary to change the centre main for every meeting, sometimes between practice and race as well. 
For the last couple of seasons I ran it with a remote Burton Ford Kent pump supplying oil to the crankshaft at 100 psi. and the Austin pump supplying just the camshaft bearings at normal Austin pressure.
The crankshaft has the rear end modified to take an Austin flywheel and the front extension ( 1 inch dia. ) in place to drive the ancillaries.

   

   

   

[Chris KC]

I guess that's the difference between racing and touring Henry - I have two of Stuart's engines and in 40-odd years of sporting road use I've never had a centre main bearing fail - replaced the shells twice but only as routine maintenance. This with over-bored A7 pump.

The problem now is finding a good shaft to start from - most are by now well-used and down an undersize or two. Although new A7 3-bearing cranks are available in Australia.

[Charles P]

You should talk to Rob Beck about re-engineering the centre main. He has a  PhD in mechanical engineering and rethinks these problems from first principles. He has a solution to the wear on the centre main

[Stuart Giles]

new A7 3-bearing cranks are available in Australia.

That looks like a Reliant SV crank and rods in there right now. Wasn't easy to find the parts for this conversion 30+ years ago when I last worked on one. We also found out the hard way that huge oil pressure is necessary to get the bottom end to live on a blown motor where the oil is feeding all the bigends via the centre main.

[Chris KC]

Judging by the centre web thickness & bolt fixing big ends I think you are right Stuart. I suppose one might get lucky, but in my own experience the available Reliant shafts now are a bit long in the tooth to justify the work involved (back in the late 70's you could still buy them new). Hence my interest in what Henry has in mind to replace it.

Interesting about the blown engines, I guess they were putting a lot of strain on the bottom end. It's perhaps of academic interest now, but I only recently realised Reliant moved the position of the big end oilways at some point in the life of the SV engine, which may not have helped.

[Henry Harris]

It is indeed Reliant crankshaft and rods. 
I hope to re-use the rods with a NOS Reliant crank that I have.
I won't be using the Shorrocks this time.