Bristol 100A engine

[Hydroglen]

I have a Bristol 100A engine and gearbox and the engine is 98% complete. I have some questions and or curiosities that some of you might help me understand.
1 When comparing it to my 85 in my Bristol 400 the most obvious external differences are the oil pan and the carbs. Triple SU vrs triple Solex. Correct?
2 The cam is different?
3 The crank is slightly bigger (2.130 diameter) than the specs I have for the 85.
Does anybody have the correct crank specs and what bearings are used. Alfa has been mentioned but year and model would help.
4 Rod journals seem to be the same as a 85
5 Pistons if stock weigh 240 grms..... Bob this may help you.The pin= 50 grms.
Pistons have a slight scallop on both sides near the pin area. Why?
6 Pistons have the number 5617 stamped on the dome. Also the diameter at 66.46 but this is Metric and = some 2.130"
7 The rod bolts are actually studs that have been pinned (see photo).
8 The rod bearing caps do not meet flush. The bearing surfaces meet, but not the outer part. Rather odd....see photo
9 Each rod is numbered but oddly. 371,376, 380, 384, 392, 400.What do the numbers mean? The rods weigh some 620 grms.
All help is appreciated, as I would like to work towards rebuilding this engine.
Other than a couple of scuffed pistons all seems to be in excellent shape.
Regards,
Dorien Berteletti

[Ashley James]

Dorien
Please have a look at the technical section of www.jel450.com for all
this information supplied by Geoff Dowdle who has done so much to help
preserve these cars.

The main specialist engine machine shop for Bristols in the UK is
Hurley Engineering Services Ltd and it's well equipped with the best
modern equipment and Paul is the nicest man on the planet. His details
are also on the website.

The 85 engine had a lighter crankshaft with non detachable
counterbalance weights with the result that when used for racing in
the Frazer Nash Cars, it kept running its centre main bearings,
overheating the oil and self destructing. It's fine for road use if
the revs are kept down. The 100 series had a bigger heavier crank
that overcame this as well as bigger valves and differently jetted
carburettors and eventually a higher compression.

Several different camshafts were used and this may have as much to do
with trying to make them last as develop more power. All Brit
manufacturers were in difficulty with cam wear at that time.

I also get the impression that the jump in power from 85 to 100 HP was
as much to do as sorting out the carburettor jetting as anything
because mine was correctly jetted according to the manual and ran very
badly until I'd made it a slight variation on a 405, again with
Geoff's help.

I'm afraid that I have yet to give the back axle to Norman because
since I'v swapped the 85C gearbox for a Close Ratio one, the noise I
attributed to the axle has gone. Early reports of the car appear to
suggest that the gearboxes were noisy. I'll still get it done before
France in June though.

Ash

[Hydroglen]

Hi Ashley,
Thanks.....but I have all the original manuals in hard copy. With regards to
engine section, they cover to some extent the 85B engines although a bit
sketchy in the valve/cam area. So this is why I asked for data on the 100 A.
I don't have the specs and I don't see them in the specs on your site.
Cheers,
Dorien

[Ashley James]

Dorien

Have you looked at the alphabetical list of Bristol Technical
Information on the same page as the Manuals? I think it answers at
least some of your question.

Ashley

[Hydroglen]

Yes, it gives me the intake valve size for the 100 A, and so it seems I
have the correct valves.
The rest is good information but does not seem to cover the points I have
raised. The Alfa connection on bearings is interesting as I have a 1300
Zagato, but there are at least 3 types of 1300 with different crank
journals. So a 750 a 101 or a 105 series? Or easier....what year?
Dorien

[Ashley James]

Dorien
I suggest that you talk to Paul Hurley as he is the leading specialist
with these engines and it will guarantee that you get the correct type
of bearing. People are selling ones that will fit but are not suitable
and all require some modification. You cannot just buy bearings and
you may make a costly mistake.

Alternatively you could contact Britain's leading supplier of pistons,
bearing, chains and tensioners for the rarer cars http://www.fwthornton.co.uk/
They've been in business since the twenties and are absolutely
first class to deal with. I believe they have some original stock.

I can't think of people better qualified to advise, though I dare say
Geoff Dowdle will have comparable contacts in Oz. Paul Hurley has
piston rings made in New Zealand for instance.

Ashley

[briwmw]

Dorien:
> If the rod journals are 1.7705 inches dia. (45 mm) the bearings are 1300 cc Alfa Guilietta which I have found to be hard to get in recent years. The MG T-series engine has the same size rod bearings, but they are not Indium lead. However, I have used them and they have held up OK. As I recall, the bearing width is correct for the small-nose crank, but has to be narrowed by 2.5mm. for the big-nose crank.
> Bill

[Hydroglen]

Thanks Bill. That's a good lead on the MG. Actually newer Alfa bearings
should also fit up to 1972 1300 engines. I pulled up all the Alfa specs
in my books and found that these all have the same journal size.
Thanks again.
Dorien