QuestionQUESTION: Howard, I have a 1975 Spitfire 1500 that had dropped its thrust bearings and the crank had bored its way into the block, making the fix likely very expensive. Instead, I was able to obtain a very low mileage 1978 Spitfire 1500 engine. A couple of questions:
1. I can’t see any, but are there any mechanical differences that would prevent me from simply moving all the components (carb, dizzy, etc.) from my 1975 engine to the 1978 one?
2. Do 1978 engines have a cylinder head designed for unleaded fuel?
3. The 1978 is a California market engine – are there any differences in the engine itself between California and Federal versions?
Many thanks
ANSWER: Hi Nigel,
It is not uncommon for the thrust bearings to drop out due to excessive ware. It was a design flaw by BLM. Each time you press the clutch pedal down you apply about 400 lbs pressure on the crank and thrust bearing. BLM for some unknown reason only uses half of a circle bearing and it wares out early. Part of the problem is the driver. It is common to stop at a light and sit there holding the clutch pedal down. This shortens the life of the half thrust bearing which is already short due to the half bearing size. So your new one is going to do the same. You need to make it a habit of putting the gear shift into neutral at lights and not hold the clutch down for extended lengths of time. Another thing I advise is to not use Synthetic oil and use conventional oil and add STP oil treatment to it. The reason I don't advise Synthetic is that you can't put STP in Synthetic oil. The STP helps keep a film of oil on that bearing.
As far as switching parts on different 1500 engines. I think all are interchangeable but there are some with lower compression that will require low octane gasoline. And some of the heads had ports in the exhaust ports for AIR. If you are building an engine with different year parts, you should find someone or some shop that builds racing engines of any kind and ask if they have a barrette for measuring combustion chambers and will measure yours to get the compression ratio so you can use the correct fuel.
There is a rough way to do it yourself without a barrette. When you finish building and installing the engine use regular gas and warm the engine up and with the engine at idle and the timing set to specs, rev it up quickly a few times and note if you get any "Pinging". If you don't get any Pinging Advance the ignition timing by 5 degrees and do it again. Repeat this until you get the Pinging on a quick throttle opening. Note the ignition timing at that point. Don't drive the car with it like that. Now drain that gas out and put in high octane fuel and advance the ignition timing by 5 degree increments until you get the Pinging again. Note the ignition timing. If you can't get it to Ping on high octane fuel then the compression ratio is probably a low compression and thus you MUST run low octane fuel. If you can get it to Ping on high octane fuel then you can use high octane fuel. But either way you MUST set the timing at least 5 degrees retarded of the Pinging setting. You can not run high octane fuel in a low compression engine and you can not run low octane fuel in a high compression engine. Leaded or leaded fuel is not an issue. It is the compression ratio and Octane rating you have to worry about. The point of timing that you get Pinging is the 5 degrees over limit. It gets complicated after that because distributor advance curves can give you high RPM Pinging that you can't hear and that is extremely destructive to an engine. Mismatching parts of an engine can be done but with care. Most race engine builders have to work with this all the time on any brand engine.
Also if either of the carburetors (Stromberg) does not have either an adjustable needle with a 3 mm Allen wrench or one of the Stromberg carbs that had a adjustable jet in the bottom. Try to get one with the adjustable needle or adjustable jet. The ones with the needle adjustment sealed and no jet adjustment either were trash and don't use it. A race engine builder can give you advice on jetting also. Always stay a little on the rich mixture side and very slowly lean it out just a little. Rich mixtures produce more power providing you don't get so rich that you foul plugs.
What you are doing can get you a much better performing engine then a stock engine but you MUST do your homework to do it.
Howard
---------- FOLLOW-UP ----------
QUESTION: Many thanks, Howard - very helpful. Do you have any thoughts on California versions of the 1500 engines compared with the regular Federal versions - are there any internal differences that you're aware of?
Nigel
AnswerAll my years were in the East so I don't remember working on any CA cars but noted different specs in the books for CA. They always had tighter emission specs then the Fed cars. Back then all the Brit cars had a hard time complying with the CA and Fed specs and keeping the cars running. Depending on your local laws for emissions on antique cars most that I talk to try to put their 75 to 81 British cars back to earlier cars like in the early 60's and put two SU carbs on them and raise the compression ratio. In the dealerships, we considered the 67 model of all the British cars as the last fast one. They all went down in power from 68 on. The late 70's did see some improvement.
For example, in 75 BLM put the 1500 Spitfire engine in the MG Midget and we got tons of complaints when the owner of a 1500cc Midget would get out run badly by a stock 67 Midget with a 1275cc engine. However, the Euro version of the 1500 Spitfire would run. They came with two SU carburetors too. Many Spitfire owners try to locate the Canada and Euro version intake with the two SU's and raise the compression ratio and end up with a good running Spitfire.
There are major and minor things that you can do to any engine to make it perform. The major ones are compression ratio, design of the intake and exhaust and the design of the cam. Any time you alter any of these you MUST alter ignition timing, match the octane of the fuel to the compression ratio and adjust the fuel mixture to match all of it. Every thing else you do to an engine are the minor things.
In your case you are mixing parts from different year engines which can net you a great running engine but you must pay attention to the details I have listed to make it go and keep going.
Howard
