MTFCA Forum

Good evening Forum Chums!

It’s been a while since I’ve been on. I got sidetracked from putting my Model T engine back together which I am doing a complete rebuild on!
Unfortunately, there was some illness of a family member that I had to deal with for the last couple of years…….I noticed in the Ford service manual. It says that the maximum allowance between the valve guide wall and the valve is .008 …….frankly that seemed like a huge number to me, but that’s what the manual says. I checked my valve Guide holes with my ball gauge and between the new .312 valves in the guide wall is consistently .004
So my question is actually two fold….. does anyone know what the valve to valve guide clearance was originally? And would you all be having a warm and fuzzy with a .004 valve to valve guide clearance!….. i’ve come this far, but if folks think I should ream it out and go with oversize valves to tighten the clearance even more, I would just love to have y’all’s opinion.
Again, thanks in advance!
Cheers!

I would be okay with .004".

Measure the valve stems. The clearance should be built in. they should measure .001-.0015 under .3125.
I go be the wiggle test. I expect .004 will feel excessively loose, in which case I, personally, would knurl & burnish the guides back to .312.
If Ford says .008 or less is ok, Its your call. Its also a matter of your performance & longevity expectations.
Modern motor specs have exhaust max @ .004 & intake @ .003. Expect extra oil burning from the looser intake valves.

too often people will go with too little clearance in a rebuild ! .004 clearance is not excessive , and is possibly a result of bell mouthing in the upper and extreme lower portions of the guide ... if .004 is the clearance measured at the extreme wear points ,then it is likely less in the middle area ... too little clearance and the valves will likely stick open ... if .004 is the extreme , then i would go for it and enjoy the car ...

You'd be surprised at the amount of lifter guide clearance you can get away with. One time I reamed the guides using a straight flute reamer with the block on a mill. Big mistake. Opened up the guides beyond Fords limit, forget the numbers. I didn't want to open up the bosses and sleeve, so I took a chance and assembled the engine. Car ran fine. It's been in the family for about 25 years. No issues.

Excess clearance can allow the valve face to scrub on the seat as it closes, which can shorten valve life. Oil consumption and carbon deposition on the back side of the intake valve heads will likely be increased. Noise may be increased. An engine run at higher speeds with sloppy clearances would probably have more issues than one run at low RPM. Modern valve materials may allow a tighter clearance than what Ford used. I'd want to minimize stem to guide clearance and maximize the accuracy of the guide to valve seat alignment. Most all running fits in engines have an ideal spec. Getting as close to ideal as is practical will assure quiet operation and long service life, and it tends to minimize oil consumption and carbon deposition. In the case of valve train fits, a good running fit at the intake valve stems allows for good mixture control, which contributes to good low speed throttle response and a smooth, stable idle.