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The 100 engine

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simon1966

simon1966

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My 100 engine is stock. I plan to pull it so that the body/chassis can get the attention that they deserve. What is the current thinking on these engines. In particular I am concerned about unleaded fuel and am curious if I am better off going for one of the replacement unleaded heads, or working with the original head. My heart says stay original, my head says maybe it is the time to upgrade the engine. Input into this decision would be appreciated.
 
If you use the original pistons, the compression ratio on these engines is low enough so they run fine on regular gas. My 100 engine had been modified back in the day with oversized high compression flattop pistons and definitely needed premium gas to keep it from pinging and running on. On the last rebuild, I sleeved it back to the original bores and pistons. It definitely lost power when I went back to original but no longer pings and I use unleaded regular gas. It is still a very lively engine and I worry just a bit less about breaking a crank or blowing head gaskets -- common problems with the 100 engine. I personally think the need for "unleaded" head modification (carbide seats) is overblown. As long as the octane is high enough to prevent pinging, the unleaded gas should not hurt your engine. If there is an issue with unleaded, it may be with severe operations with sustained high speeds, not likely to be an issue with most street Healeys. p. s. check your head carefully when you rebuild. Cracks are common that leak water and erode the valve seats whether they have carbide inserts or not. I did buy a Welsh head because of cracks in mine, but I have not installed it yet -- the cracked head works OK but if definitely limits the life of my valve seats.
 
Incidentally, the 100, and most 100/6 engines, were manufactured before they started putting lead into the gasoline, sometime in the late-late 1950s, according to my (also late...) father.

If I was doing a valve job and needed seat work anyway, I'd go with either induction hardened or hardened inserts. I don't know if this was a result of a singular poor quality installation, I did have one (1) seat become dislodged on an MGB engine__amazingly with no collateral damage.

If you're having to make regular adjustments to the valve clearance (as a result of valve seat recession) then it should be addressed, otherwise, I agree with Healey 100's statement above.
 
In general, running an unleaded engine without valve work isn't a problem for normal useage. However if you are stripping the engine and have the head off then it makes sense to have the exhaust valve work done at the same time. 100 heads are prone to cracking so the next step is an aluminium head. The ones made by Denis Welch are FIA approved but they are pretty expensive.
 
Your standard head will work fine with unleaded fuel unless you plan on towing heavy loads for long distances. Unfortunately it will almost certainly be cracked to some degree and this will most likely determine how you proceed. There was a recent thread on the same topic. Andy.
 
THanks for the input. Very clearly I will need to get the head inspected by an expert to gauge its condition. Since it is 59 years old I guess it should be expected to show some wrinkles!!
 
I had hardened valve seats fitted to an A90 Atlantic cylinder head about 18 years ago. Australia went lead free in the mid 80s.
I have had no trouble with the head since.
Can you still get 'soft' valve seats?
 
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