A little background info. I have a low mileage original engine in my 1922 TT fire engine. I decided to replace the original valves with new stainless steel valves. What noticed is the new valves are .03 to .05 shorter in overall length when compared to the original 92 year old valves! Which results in an increase in valve clearance from an average if .015 with the old valves to as much as .020 with the new valves. Is this something others have noticed as well? If so is there any explanation as to why? I have not decided on the type of valve adjustment procedure to use yet. I guess I' m deciding between the KR Wilson method and the method outlined in the MTFCA engine book. Apparently setting them to .010 and 012 is out of the question unless I grind the seats enough to lower the valves in the block. Which I really do not want to do condidering they are in very good condition. Your thoughts on any or all of the above are appreciated.
I should also change the tappets to the adjustable Than you can adjust your valves very easily.
I agree with Andre on the adjustable lifters. Not sure why the new valves are shorter, but what you might find is the tappet has worn a bit where it meets the valve stem.
My '27 motor has a such a depression there you cannot measure valve tappet clearances accurately at all.
As for what method to use... I considered the same when rebuilding the '13 motor, but decided I wanted the cam perfect, so i went for a reground cam. Now I set every valve at 0.015" and all cylinders are filling properly and evenly etc.
Hope this helps
You should not grind the seats further. The valves ideally should be 50% proud of the block surface. If the valves sit flush with the seats (for example) then airflow is hurt substantially.
You can buy valve stem caps to add dimension to the length of the valves. They are sometimes called "lash caps". Any good automotive machinists supply sells them in a variety of diameters.
I appreciate everyones comments so far. As for my tappets they are as square are straight as new. The engine is still standard bore and the pistons fit snug in the cylinders. I would like to keep this motor as stock as possible as it will be seeing little use. I may explore the option of valve stem caps. It is just sad I have to resort to that. Why can't they just make the valves as long or longer than my 92 year old valves and let me grind them to fit?
You say the valves are up to 50 thou short, but only increase gap from .015 to .020. That doesn't make sense to me...other than there are differences in the valve head height.
However, with an original T, you don't want .015 clearance...you want to set your valves to piston travel with exhaust/intake opening/closing at specific piston travel. This is discussed in the Model T "bible" for setting valve events to a worn cam. You can get excellent performance from this method on an older car (this is NOT the KRW tool method of pistion height vs valve travel, so don't be confused).
The only way a T is going to run its best with .015 lash is with a brand new cam that has identical lobes and is designed for that gap/lash. Any other time that it has .015 lash is either a fluke/coincidence or just plain wrong (not understanding the difference between a new cam and a used cam).
Yes I agree with Royce. The stainless valves are
shorter; the choice; adj lifters or valve caps that
comes with internal shims. The quick way simple
with the valve installed (even with engine in car)
just lift the valve up install the cap and lash it
adding or removing shims (disks). Any racing supply
like Summit. bought mine, eight caps 12 bucks.
another plus is, down the line its easy to adjust lash by adding another shim. shims are inside the
caps x .001 or .002. So dont grind seats or it will
end up on a milling machine for seats, someday.
If you have a low mileage original engine, setting the lash at 0.020 I think would work fine. If the cam is well worn, then setting the valves by the K.R. Wilson method will give you a better running engine, but probably noisy valves.
On my original 24 engine the cam was excellent, so I set the valves at 0.012 clearance. Just for kicks I checked them versus piston travel and they all were the same.