401 or 403 cam ?

[RALPH M]

New member here so hope I am doing this correctly. I now have a 1951 401, chassis 903 and an engine with a 403 head. It is a running car and I would like to get it running more smoothly but before I take it to my local garage with the rolling road I want to try and find out whether the motor was rebuilt with a 401 or 403 cam. I know for sure it is a 403 head. I understand the valve lift is the same on both so the only way I can think of is to try and measure the dwell angles. BUT.......with the engine in place! One idea is possibly to fix a temporary protractor to the pulley?.. then turn the motor and with a dial gauge on one of the rockers watch the point of lift. Perhaps I am crazy.

My reason is to be able to put the right jets in the carbs and rebuild the Lucas distributor with the correct springs before taking her for the tune up.


Any suggestions welcome.

[Geoff Dowdle]

Ralph ,
your 401 chassis 903 was delivered new in Sydney/Australia &restored in Sydney between 1973 - c1976 .
The engine at that time was Block 85A/1471 (ex 400/639) and head 100A/3137 (ex 403/1430, and the only 403 part in the car, as 403/1430 is a good original car that just had a replacement head at one time) , my guess is that it had a standard 401 cam.
During the restoration, parts of 401 chassis 990 were also used.
I knew the last 4 owners in Sydney , the last of which sold it back to UK in c1987.
The engine could have been rebuilt since then but I doubt it very much as it is unlikely to have covered many miles since 1976.
The complete original engine of 401/903 (85C/1815) I sold to a chap in Yorkshire in 2015 but has not fitted it to another Bristol yet.
I suggest you check the condition of the Solex carbs and record all the jet and venturi sizes, plus strip, check and lubricate the distributor before you consider a major tune up . These are difficult to tune especially by people that have no experience with them .
In my 40 plus years owning and tuning Bristol 6 cylinder engines, one of the major problems is correcting all the poor workmanship that occurred previously, carbies in particular. Float levels are often way too high.
Does the engine have a Top Dead Centre mark?

Geoff

[RALPH M]

Many thanks Geoff for such a quick and informative reply. John Healey had kindly passed on to me a lot of copy emails between yourself and him regarding my car's history but you just added some more snippets of information. I can never get enough history on a car as it is so fascinating and part of what the car is. Thanks also for the extra images; 16000 Au dollars back along! Yes, the engine still has the same numbers as you mention. I wonder why the then owner took the original motor out and what was it's condition when you sold it to the chap in the UK?

I have all the brake system off the car at the moment but by next week she should be back on the road and also stopping better.

I will check to see if I can find a TDC mark on the pulley which will be a start. The carb jets are all as for the 401 spec. As you mentioned the source of the head it does point to it still being being a 401 cam but it would be better to know for sure.

best regards

Mike Ralph