Well I finally got the heads off and now I am curious what kind of bores I have. The engine serial number says its out of a 72 (the car is a 73.5 T) and it looks as if someone has been in there before...well before it seized do to rain down the Webers. Anyway I put a magnet on the walls of the bore and it grabs pretty good. Im just kinda confused what this means, I have looked around and gotten mixed answers depending on the year of the car. I would like to have the bores cleaned up instead of purchasing all new ones. Is this possible?
Thanks for all your help guys.
Nick
73.5 T
Piston liner question
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Bob_Salmon
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Sounds like you have Biral cylinders Nick. THey have a thin steel sleeve which is encased in the finned alloy unit. The metal sleeve is not removeable but it can be re-bored if the damage is not too bad. That will then require an over size set of pistons but still much cheaper than replaceing the whole set of six cylinders.
Bob
Bob
Rust - what holds the holes together......
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Lightweight_911
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TargaNick
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Thats interesting, the cylinder's are not that flat they are somewhat concave and they have grooves for the valves on the top. I can get some pics if that would help? Also if it was cast iron would a magnet stick to the sides? I know someone has done something to the engine previously I just dont know what. Thanks for your help guys.
Nick
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Lightweight_911
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Barry
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One quick tip: when you re-assemble the engine, double check that your valve-piston clearances are O.K.:
Build up the engine, with heads torqued down. Leave all valve clearances well loose (like 30 thou). Pick a cylinder from each bank and one by one, close the valve clearances for the exhaust and inlet of your chosen cylinder as follows: position the cam as you would for adjusting the clearances as usual (i.e. TDC on compression stroke). Adjust out all clearance, and then keep turning: each turn represents 1mm travel. From memory you are looking for at least 1.5mm for intakes and 2.0mm for exhausts.
Therefore to be safe on an exhaust valve, you should be able to close it's gap, wind a further two turns, and very carefully turn the engine through two turns at the crank: i.e. a full cycle. Obviously you are doing this very carefully, one valve at a time (you don't want to bend a valve!): interestingly it's not TDC that's the problem, the valves actually get closest to the piston a little way before and after TDC. The inlets obviously would be wound down 1.5 mm. Once the checks are done, all of the clearances can be set to the factory spec.
Sorry, forgot to say why you need to do this check (
): the E piston has quite a crown on it compared to the T piston, as a consequence if someone has modified the engine, and particularly fitted hot cams and had some machining done, the piston to valve clearance gets very tight. When the engine is revved, the con-rods get longer as they stretch, risking a contact. I've heard of engines making an odd noise on start-up, that dissappears after a minute or so: turns out it is the valves just kissing the pistons until the barrels warm up, expand, and take the pistons a liitle lower in the bores 
. So this check safely replicates an engine going slightly beyond maximum revs, perhaps a bit of valve bounce, hot valves and all of the other things that could combine to make clearances tight.
One of the donor engines for my original 911 was a T engine with E pistons and S cams: surprise surprise, when (the long term non-runner) came apart, it was to the tinkle tinkle of exhaust valve head in the bottom of the barrel. Further investigation showed every exhaust valve had failed, and the heads could be snapped off the stem by hand . (Not a happy day in the workshop 
).
Build up the engine, with heads torqued down. Leave all valve clearances well loose (like 30 thou). Pick a cylinder from each bank and one by one, close the valve clearances for the exhaust and inlet of your chosen cylinder as follows: position the cam as you would for adjusting the clearances as usual (i.e. TDC on compression stroke). Adjust out all clearance, and then keep turning: each turn represents 1mm travel. From memory you are looking for at least 1.5mm for intakes and 2.0mm for exhausts.
Therefore to be safe on an exhaust valve, you should be able to close it's gap, wind a further two turns, and very carefully turn the engine through two turns at the crank: i.e. a full cycle. Obviously you are doing this very carefully, one valve at a time (you don't want to bend a valve!): interestingly it's not TDC that's the problem, the valves actually get closest to the piston a little way before and after TDC. The inlets obviously would be wound down 1.5 mm. Once the checks are done, all of the clearances can be set to the factory spec.
Sorry, forgot to say why you need to do this check (
): the E piston has quite a crown on it compared to the T piston, as a consequence if someone has modified the engine, and particularly fitted hot cams and had some machining done, the piston to valve clearance gets very tight. When the engine is revved, the con-rods get longer as they stretch, risking a contact. I've heard of engines making an odd noise on start-up, that dissappears after a minute or so: turns out it is the valves just kissing the pistons until the barrels warm up, expand, and take the pistons a liitle lower in the bores . So this check safely replicates an engine going slightly beyond maximum revs, perhaps a bit of valve bounce, hot valves and all of the other things that could combine to make clearances tight.One of the donor engines for my original 911 was a T engine with E pistons and S cams: surprise surprise, when (the long term non-runner) came apart, it was to the tinkle tinkle of exhaust valve head in the bottom of the barrel. Further investigation showed every exhaust valve had failed, and the heads could be snapped off the stem by hand
. (Not a happy day in the workshop ).
Last edited by Barry on Thu Aug 31, 2006 2:40 pm, edited 3 times in total.
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Barry
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BTW, I got rid of the S cams and went to E (well Solex anyway) cams, which were perfect: went from .7mm clearance to over 2mm on the exhausts.
I was lucky, I nearly didn't bother with the piston-valve clearance checks, and did it almost on the offchance, not expecting to have any problems. Had I run the engine as it was, it would have almost certainly had problems when it was first revved. It was great to know that those clearances were huge, and that I didn't have to worry about them
.
I was lucky, I nearly didn't bother with the piston-valve clearance checks, and did it almost on the offchance, not expecting to have any problems. Had I run the engine as it was, it would have almost certainly had problems when it was first revved. It was great to know that those clearances were huge, and that I didn't have to worry about them
.DDK Member1243 07741 273865. Home of the RY Austin 7 Trophy's and Austin Single Seat Racers