Building a car can have enormous frustrations, the worst of which is having to go back and redo something you though you had already dealt with. In my case it's a badly smoking engine - the smoke is blue so I know it's burning oil. I thought it was an excess of oil pressure but I have changed the pressure relief spring and the bloody thing is still doing it there is no way it will pass the IVA test with it as it is so something needs to be done.
There are essentially 3 ways oil can get in to the combustion chamber - via the fuel, past the piston rings or via the inlet valves. It's fairly easy to run some tests, the easiest and the first one I tried was using new, clean petrol - that made no difference. The second thing it is sort of possible to eliminate is leaky piston rings. You can do that to at least some extent with a simple compression test, if one or more cylinders are down on the others you know you have a bad cylinder. It's not 100 per cont conclusive though as it can happen that the compression rings are good and the oil control rings are bad but that is frankly a highly unlikely scenario. My engine is a 10'5 to 1 compression ratio so a totally perfect engine would be 10.5 bar or 151 psi. All 8 of my pots were between 140 and 145 on my cheap Chinese gauge, no pots were way down so I am very happy with that, it means my bottom end, bores, pistons and rings are all good - I don't need a new engine.
Having eliminated 2 out of 3 Sherlock Holmes would tell you that the third scenario has to be the one, it's not elementary though so more research is needed. Now then, my engine was made in 1972 or 3, back then they did not fit oil seals to either the inlet valves or the exhaust valves so any wear in the valve stems or guides will result in oil being able to get between the two. When you open the throttle you get a significant vacuum, which sucks any oil in through said gap, this gets burnt, blue smoke is the result. Latter engines had o rings fitted, later ones still had top hat seals fitted to the inlet valves, later still they fitted seals to both inlet and outlet valves, this was a result of emission standards getting ever tighter.
This is all my fault really, when I rebuilt the engine I did the cheapskate thing and assumed that the valves and guides would be ok, I ground the valves in to make sure they sealed but I did not put new valves or guides in, I should have done so and now I have to fix it. The question is - how? Well firstly the heads come off without getting the engine out, I only have to remove the exhausts, the carbs and inlet manifold and not a lot else. 14 bolts hold each head down, I will need new gaskets for when it all goes back together. Heads are fairly similar right across the production run but some of the later heads have bigger valves, which give better gas flow and therefore bigger power, it therefore makes sese to go with a later head. It should be possible to get a pair that are less worn than my 52 year old ones, that have the better flow and the seals, which can be changed for nice new ones. A new pair will be about 120-150 quid or thereabouts, not exactly a King's ransom. I won't have to sell much of her jewellery to make that much.
There is possibly a cheaper way, enter the Payen HR336 valve stem seals as fitted to a number of cars from various manufacturers, they fit the early valve guides perfectly and can be had for about 4 quid each, I only need 8 as it's the inlet valves that are the issue. It may even be possible to fit them without removing the heads, I shall look in to that. I might have to make a tool to do it but it would save me having to buy new gaskets and I wouldn't have to drain coolant etc - decisions, decisions.
I am tempted to go for the later heads anyway and maybe even see about getting a holley 4 barrel carb at some point to pep things up a bit. My engine as is should produce about 160 BHP, no exactly beefy by today's standards and much less than I have had in any car for the last 20 years, excluding my current diesel Insignia. With the SD1 heads I should gain maybe 20 BHP, a mild cam and a decent carb / manifold might push me over the 200, which would be a lot better. I shall have a sleep on it and see what I feel like in the morning.
I slept on it, decided the advantages of the later heads with much better gas flow could only be a good thing so set about finding a pair, which proved to be both interesting and challenging. Firstly I had to understand which heads would be best, they changed numerous times over the 50 odd years of production. The earliest heads were out as they had no facility for seals at all, the next earliest only had o rings that were prone to premature failure, the next ones had seals on the inlets but not the outlets, the very latest had seals on both but also had smaller combustion chambers, which gives too much compression with the pistons that I have in my engine. You can lower that with a thicker composite head gasket but the ones I have found are casting number ERC2016, which were fitted to the SD1's and then later to the 3.9 injected engines. They have the same size combustion chamber but bigger valves, the inlet valves are wasted and ground to a different angle, it all aids gas flow and gives better top end power. It's almost worth doing just for that. They were only 75 quid the pair, they will need a clean up and the valves grinding in I suspect, they will certainly need new seals and new gaskets. They should arrive in the next 3 or 4 days, I will get to them once I have finished the bodywork stuff. It's alarming how much some people ask for these things, many of the full time dealers want over 200 quid a pair but you can pick them up at auto jumbles for a fraction of that, just be careful that you get the right ones, there are a number of variants. They will all fit but you may need to use different gaskets, the later heads all flow better then the earlier ones. Another interesting thing I found out is that the heads are available in both 10 and 14 bolt - mine are 14. The latest ones are all 10, the extra 4 bolts were outboard of the mating surface and were found to cause problems by putting pressure on one side of the head only and causing gasket failure. The advise now is to either use a 10 bolt head or if you use a 14 only do the outer 4 bolts up to about 20 lbft of torque. Some people leave the bolts out altogether, which is what I will be doing.
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