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

[Geoff Dowdle]

Dorien ,
I have a limited supply of Alfa conrod bearings , what size do you require.
Six of the 12 shells need drilling to feed oil up the rod to the gudgeon pin
.

The Bristol manual has supplements at the rear of most sections covering the
403 specs (100A engine)

Regards
Geoff

[Hydroglen]

Geoff,
Thanks for your offer. I am still attempting to make sure of what I have,
and then will see what size bearing shells I will need. Being Alfa there is
a good chance that I may have some, but at this point it is a guess until
the correct model can be determined.

My Bristol 400 manual does not cover the 403 specs and only covers my
400. Once I can find the crank specs I will see how close to spec I am. I
like to keep the mains and rods to the same spec ie: standard, -10 and so
forth.
Worst case I can chrome and or cut the crank and rebabbitt all the shells
and machine to size.

Regards,
Dorien

[412usa]

Dorien,

I took the opportunity to look at several pistons from two of my BS1 MkII
engines, which are based on the 100 series engines. Also I have included a
bit of history on Chassis 3020 (engine 219) to see if racers like Bill can
shed any light on the early history and the anomalies of two or three rings
in the same groove.

Engine 219, which was extensively raced had a huge 0.110 top compression
groove and was fitted with two or three rings (depending on the piston
number). This engine also had a very high compression which lead to failures
of the head gasket. I have been able to track down and talk to a number of
owners as far back as 1964, but the racing history is sketchy. Serge
Dermanian, who now runs the auto museum of Prince Rainier in Monaco, sold
the car from High Performance Cars in Waltham, Mass. but said the car really
belonged to Autolab Import (owned by Skip Barber) but had been sitting there
a while and so Peter Sacks (sp?) took the car to sell. Serge had fitted two
gaskets because the head had been milled so much. The previous owner, Albert
VanDam had said that the car was raced by a Greek mechanic called Makinon
(or Macadon) and a fellow called Felix Brossard. Serge said that Brossard
looked after Gaston Andrey's Birdcage Maserati. However, I have not been
able to confirm the ownership or any racing heritage. However, it might be
that during this time the top ring combination was installed.


Engine 294, which I don't think was raced, has the spec 0.093 top
compression groove. The specs for the pistons on both engines are as follows
(inches):

Engine BS1 Mk II 219: Piston 1.
Crown 2.582
Skirt non-thrust 2.588
Skirt thrust 2.596
Top compression groove 0.110
Second Compression groove 0.08
Third Compression groove 0.08
Oil scraper groove 0.156
Weight 234.9 g.

Engine BS1 MkII 294 Piston 4.
Crown 2.584
Skirt non-thrust 2.592
Skirt thrust 2.596
Top compression groove 0.093
Second Compression groove 0.08
Third Compression groove 0.08
Oil scraper groove 0.156
Weight 233.8 g.

Note that the pistons are oval and tapered to allow for expansion of the top
and non-thrust skirt at operating temperatures.

Best Wishes for the New Year to all.

Peter McGough

[Hydroglen]

Peter,
Good information. If by chance you have the specs for the 100A crank that
would be great.
Dorien

[412usa]

Dorien,
I don't have a manual for the 403 but I think the key is to find out if you
have the small or large nosed crank. I can fax you pages from the 100 C, D
and D2 manual which covers both cranks and you can compare. The 405 manual
gives the same info but is not as clearly printed. However, I don't have
anything definitive on the 403 100A engine. The Arnolt uses the small nose
crank although with a different part number than the early 405 small nose
which is also a different part number to the early small nose on the C, D
and D2 series! Confused yet.

I will send you the scan of the crank data page and you decide.

Peter

[Ashley James]

It's always the top ring that wears out and also opens out it's
groove, so it's conceivable that the ring groove has been turned out
and a wider or more than one ring fitted. I have some Dennis Fire
Engine Pistons here from a Rolls Royce B80 and their top ring is
steel with a Molybdenum coated on its contact surface. This is
because R-R had difficulty persuading drivers to warm the thing up
carefully before driving off!
Ash

[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