Moral tale

[alfazagato]

I had my 750 SZ head attended to by specialists. They checked and re-faced the seats and valves checked the guides and set the shims. The original valve stems were for some reason slightly shorter than standard, but only by a few thou. All very satisfactory on start up. However, it turns out that they used on the inlet valves to no.2 and 4 cylinders Land Rover shims which are indeed also for an 8mm valve stem.
The upshot of all this is that the LR shim has a deeper skirt than the AR part and when the engine became hot, the shim revolved and caught on a high spot on the collets thus effectively removing clearance, holding the valve slightly open and allowing a reduction in compression. The fact that when the engine was cold and produced excellent compression and the cylinder leakdown was better than good, gave no indication of this problem.
So moral of the story is to measure the skirt depth as well as the shim thickness. We machined the skirt to the AR depth and all is well (I hope!)

[alfadak]

Quite enlightening! I think that Rover parts are pretty rare in the States, but it is worth knowing that those parts are interchangeable with the right modifications. Glad that all is well that ends well.

[alfazagato]

Actually, I believe that there are generic 8mm spacers which fit a variety of engines, I can't blame Land Rover...their name just happened to be on the packet.

[AR58SprintV]

Dear Stuart,
However did you get an Alfa engine HOT in London this time of year? Since you can, I have heard that Alfa 2.0 twinspark heads also use the 8mm shims, I'd better double-check!
Keep warm,
Laurence of Berkeley

[alfazagato]

Lawrence you are following the well worn route of rotten weather, even worse food and refrigerators made by Lucas. Well no longer, don't tell anybody but the recent temperatures in London were well higher than SF, the foods is as good and well the beer is beer. You keep threatening to come over....do!
Use a winter thermostat and lo and behold, a warm engine, well 85C ish and the SZ heater actually works too. Do check all your shims, take seconds saves major expense. Also check valve stem lengths before assembly as the combination of the stem length and shim depth was my downfall.

[yvesmontreal]

Quote:

Originally Posted by alfazagato Do check all your shims, take seconds saves major expense. Also check valve stem lengths before assembly as the combination of the stem length and shim depth was my downfall.

[Andrew]

I have run into shims with longer skirts, and having exactly the same problem. Drove me nuts setting the valve clearances, when I'd change a shim by .001 or so, and have radically different clearance measurement, because the skirt was hitting the keeper. I too filed off the long skirt and all was well.

But what are these long-skirt shims for? They came in a big lot of Alfa shims, and I didn't til this time know there was a difference.

Andrew

[alfazagato]

I think they are a generic 8mm shim (used in later Alfas?). Now we know.... its at least half the problem.