Bristol Engines

[UK6]

Tom,
Re overboring cylinders whilst keeping the external dimensions of the
block the same - I think that you will have insufficient sealing area
between the bores. The original engine is already marginal in this area!
The other issue, as correctly pointed out by Geoff Dowdle, is that a
substantially overbored block from say 66 to 75mm diameter would
encroach/erode your main bearing area of your block.
In short, if you increase your bores to enable 2.5L or more you need a new
longer block casting and crankshaft. Hence my TR 2500 engine block and
crankshaft suggestion earlier. Can I suggest that you have another look
inside any block and you will see what I mean.

I guess you could design a "modular" engine with different stroke
crankshafts and vary the rod length. Unfortunately the 6cyl Bristol motor is
already substantially undersquare and thus increasing the swept volume by
increasing the crank throw and fitting shorter rods would be a backward step
in efficiency. I think that most designers just set out to optimise the bore
to stroke ratio and allow say, a 3mm overbore capacity.

Regards,

Brett

[Jonathan Lingham]

Might this new fangled 3D printing provide a cost effective way for fabricating patterns for heads and blocks? Anyone embraced this technology yet?

[James McClure]

I must admit that I've been thinking of selling the motor and gearbox from my 401. Then possibly installing a 2.4 Jag motor, which I have. Hopefully not much weight added, as the 2.4 is lighter than a 3.4, though I have no info as to how much less.

Then the 401 would be driven more, with less chance of being stolen and gutted for a fake Ace, etc.

[Kevin H]

Originally Posted by Jonathan Lingham

Might this new fangled 3D printing provide a cost effective way for fabricating patterns for heads and blocks?

I don't think plastic blocks and heads would work very well

Originally Posted by James McClure

I must admit that I've been thinking of selling the motor and gearbox from my 401. Then possibly installing a 2.4 Jag motor, which I have. Hopefully not much weight added, as the 2.4 is lighter than a 3.4, though I have no info as to how much less.

The Jag engine and manifolds would need to weigh roughly the same as the Bristol engine. Isn't the 2.4 a small V8? lovely engine but would it fit width wise?

Then the 401 would be driven more, with less chance of being stolen and gutted for a fake Ace, etc.

How does that work - would you have a sign on it saying "Not worth nicking cos it has a Jag engine" ?

[Jonathan Lingham]

Kevin

The clue is in the word "pattern". My (serious) suggestion was to consider using 3D printing to make a pattern of the needed part in plastic, not the part itself. Then use this in a mould to cast the part in iron or aluminium, using the lost wax process. Must be vastly cheaper than constructing a pattern using traditional processes.

The Jag 2.4 is a straight 6 in the XK series. Fine design for its time, long stroke, a bit limp compared with its 3.4 and 3.8 litre brethren. You may be thinking of the small V8 that Jaguar fitted in the 250 and Dart. Nice, compact, but I think you may be right that it might be a bit tricky to slip into a Bristol. But maybe it's been done.

Selling off the original Bristol engine and replacing it with another unit sounds sacrilegious to me. But if it must be done, why not emulate AC, and slip in a 2.6 litre six cylinder Ford unit from a Zodiac. It's what they did with the later editions of the Ace and Aceca. So not that awful, and there is a distinguished precedent.

[Kevin H]

Originally Posted by Jonathan Lingham

Kevin

The clue is in the word "pattern". My (serious) suggestion was to consider using 3D printing to make a pattern of the needed part in plastic, not the part itself. Then use this in a mould to cast the part in iron or aluminium, using the lost wax process. Must be vastly cheaper than constructing a pattern using traditional processes.

Oops! I'm sorry Jonathan, and somewhat red faced

[James McClure]

Originally Posted by Kevin H

The Jag engine and manifolds would need to weigh roughly the same as the Bristol engine. Isn't the 2.4 a small V8? lovely engine but would it fit width wise?

The 2.4 is a short stroke 3.4 straight 6, and is almost 2" shorter, so should be lighter also. Nice looking engine and I already have one, with triple 1/1/2" SU's!

[HughMiller]

InRacing in Nottingham seem to be energetically using new technology to simplify the manufacture of replacement parts in all kinds of impressive ways, so they might well be using 3D printing to make patterns. They do make new 2-litre heads and blocks already. The fitter who showed me all all this didn't know how much a new block would cost. It might be a matter of 'if you have to ask the price, you can't afford it'.
Hugh