The Ford Barn

tubman · 11-10-2015, 06:28 PM

OK. I have been looking all over the internet trying to find what the acceptable run-out should be for a flathead crankshaft. Very surprisingly, there seems to be no information on this. Just about everything I looked at said that proper bearing clearances are much more important than run-out. The one place I did find some actual numbers were on snowmobile forums. This is typical of what I found :

"I have heard between 2.5-3 thousands are factory spec so the question is how far does one let the crank get out of spec before repair? 4-5-6? What is a good measure to tell when the crank is on its last legs or could benefit from some preventative maintenance."

I have owned a few snowmobiles, and all of them had a red-line of over 10,000 RPM. From this, I have to believe that "less than .003" would be more than adequate for a flathead. Therefore, I stand by my initial statements.

I have spent some time and money determining these facts, which I believe will benefit the majority of members here.

I hate to have to say this, but unless you guys can come up with some solid, verifiable numbers, "37 Coupe" and "Kube": stay out of this thread; you have nothing to add but negativity, and that hurts everyone.

11-10-2015, 06:28 PM	#10
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 12,148	Re: Another myth put out to pasture OK. I have been looking all over the internet trying to find what the acceptable run-out should be for a flathead crankshaft. Very surprisingly, there seems to be no information on this. Just about everything I looked at said that proper bearing clearances are much more important than run-out. The one place I did find some actual numbers were on snowmobile forums. This is typical of what I found : "I have heard between 2.5-3 thousands are factory spec so the question is how far does one let the crank get out of spec before repair? 4-5-6? What is a good measure to tell when the crank is on its last legs or could benefit from some preventative maintenance." I have owned a few snowmobiles, and all of them had a red-line of over 10,000 RPM. From this, I have to believe that "less than .003" would be more than adequate for a flathead. Therefore, I stand by my initial statements. I have spent some time and money determining these facts, which I believe will benefit the majority of members here. I hate to have to say this, but unless you guys can come up with some solid, verifiable numbers, "37 Coupe" and "Kube": stay out of this thread; you have nothing to add but negativity, and that hurts everyone. Last edited by tubman; 11-10-2015 at 06:35 PM.