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Triumph TR6 - Hot v. Cold Lash Specs
|Any rule of thumb on converting a hot valve lash spec to a cold clearance? Add 0.002 to the hot spec?|
|Rick this interested me too.|
Owners manuals say 10 thou intake 12 thou exhaust, set cold. This is generally taken to be room temp; I have read you must leave the car as long as 24 hrs after driving to be sure all heat is gone.
Two years ago I installed a cam from Kent Cams, very high performance, clearance 22 thou inlet 24 thou exhaust, set hot (how hot? presumably cool enough to work on with bare hands, perhaps between events at the track).
I emailed Kent for clarification as it seemed like a big difference and was told the numbers were correct.
I assume the big difference is partly due to temperature, partly to camshaft design.
|So, how did you set the lash initially after the Kent cam install? I'm in the same predicament with my new Isky cam that has a hot-only spec of 0.016. My inquiries to Isky have not been answered.|
|Forgot to mention that the wider lash specs have to do with giving the lifter more time (cam degrees)to leave the base circle portion of the lobe to the ramp portion before driving the rocker arm to the valve tip (and vice versa). Why this is so I don't know, perhaps to minimize shock.|
|Get the engine hot, then set the gaps to 0.016" as Isky specifies. Then let the car cool down for 24 hours and measure the cold gap. From that point on, you can set the gaps cold. And when the engine gets hot, you can occasionally re-check them hot.|
Don Elliott, 1958 TR3A
|Thanks Don. I was asking since this is a first-time install where I don't know what the cold setting is in relation to the hot. Guess I'll put it at 0.018 cold and go with that.|
I thought the 6 cylinder had both exhaust and intake set to 10 thou (cold). Have I been doing somthing wrong for the past 3 years?
|Rick- These #'s are all hot cams specs. It has been so long since I installed mine I can't remember what the Spec is any more. |
|I was at a British car shop one time and the mechanic was working on an immaculate A-H 3000. The mechanic was a Brit import, and he was setting the valves WITH THE ENGINE RUNNING (at idle). He was using a feeler gauge and adjusting the rockers. I asked him about his method, and he said that it was a method he had learned in England, and felt that it was more accurate than setting the lash when the engine was static. From my watching, it appeared that he was trying to get the quietist setting, yet still able to get the feeler gauge in. He was using three different gauges (don't know which ones), to determine if it was too tight, too loose, or ok. I've never tried his approach myself - have any of you?|
|I've tried to adjust the valves with the engine running and all I managed to do was mangle my feeler. Definately a method that takes some experience! But it is advisable to a least observe the valves while running to ensure the motion looks even and that the top-end oiling is good. That's how I noticed my #11 lobe was wiped and got me into my winter project.|
I finally heard from Isky and they confirmed my gut feeling: the cold spec is 0.002" wider than the hot spec. It would be different for an aluminum head. I believe the spec for the stock cam is 0.010" cold, not hot (which implies the hot spec is actually 0.008").
|If you have a spec that says "hot", it means you run the engine up to temp - then turn it off and set the valve clearances "hot". If you try it with the engine running, you have oil splashing everywhere and your 0.010" feeler gauge quickly becomes 0.008".|
Don Elliott, 1958 TR3A
This thread was discussed between 10/03/2004 and 11/03/2004
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