The Ford Barn

Cecil-Indiana · 06-19-2011, 06:34 PM

Gentlemen I've got a mystery here. I rebuilt my 50 Merc engine and found it had a bad rear main leak. When I took it back down I found the rear seal dia. was scored bad. I have a nice 49 engine so I swapped the cranks and the pistons were hitting the Offy head. I think I've just now solved the problem by using 2 head gaskets. Both cranks were dusted .010. Anyone ever run into this situation? Keep in mind all I did was swapped cranks and then I had a bad knock which turned out to be the domed piston hitting the head.

Barlea · 06-19-2011, 07:01 PM

Maybe crank number one was a Ford and now you have Ford pistons on a Merc crank? ..B.

George/Maine · 06-19-2011, 07:18 PM

You are only talking about .010 not 1/4 inch right.
When the crank was ground the stroke must have been on plus side.Thats how they get more out of a stock crank.

Barlea · 06-19-2011, 08:26 PM

.010 more stroke wouldn't normally cause contact unless clearance was pretty tight with crank number one, right? 1/4" more stroke is 1/8" more into the head. Not even all the pistons would hit on Merc heads, I'm thinking, but I could be confused. ..B.

waldo · 06-19-2011, 09:08 PM

I can vouch for the fact that 4" stroke with Ford pistons will just kiss 8CM heads. I bought a swap meet engine, just out of the machine shop, and it was assembled as above. It had a wicked exhaust rap and lots of comp. Turning over with a wrench, it would lock up after half a revolution. Two Best gaskets with copper spray gave me a .055 clearance and a super running engine. Domed pistons with, now, Offy heads. I had to put .060 spacers under the plugs to keep the gap from closing up at high rpm. I ran this one in my H.A.M.B. HA/GR dragster last year and it held up fine. Going to run an old Bonneville engine this year.

Ol' Ron · 06-19-2011, 11:15 PM

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This lowers the CR drastically. Why not have the heads redomed or get a new set of heads.

waldo · 06-20-2011, 07:40 AM

The .055 piston to head clearance gives good comp. The intake valves were closing the plug gap.

06-19-2011, 06:34 PM	#1
Cecil-Indiana Member Join Date: May 2010 Location: Muncie, IN Posts: 72	Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? Gentlemen I've got a mystery here. I rebuilt my 50 Merc engine and found it had a bad rear main leak. When I took it back down I found the rear seal dia. was scored bad. I have a nice 49 engine so I swapped the cranks and the pistons were hitting the Offy head. I think I've just now solved the problem by using 2 head gaskets. Both cranks were dusted .010. Anyone ever run into this situation? Keep in mind all I did was swapped cranks and then I had a bad knock which turned out to be the domed piston hitting the head.

06-19-2011, 07:01 PM	#2
Barlea Senior Member Join Date: May 2010 Location: West Central Alberta Posts: 441	Re: Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? Maybe crank number one was a Ford and now you have Ford pistons on a Merc crank? ..B.

06-19-2011, 07:18 PM	#3
George/Maine Senior Member Join Date: May 2010 Location: Mid coast Maine Posts: 1,878	Re: Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? You are only talking about .010 not 1/4 inch right. When the crank was ground the stroke must have been on plus side.Thats how they get more out of a stock crank.

06-19-2011, 08:26 PM	#4
Barlea Senior Member Join Date: May 2010 Location: West Central Alberta Posts: 441	Re: Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? .010 more stroke wouldn't normally cause contact unless clearance was pretty tight with crank number one, right? 1/4" more stroke is 1/8" more into the head. Not even all the pistons would hit on Merc heads, I'm thinking, but I could be confused. ..B.

06-19-2011, 09:08 PM	#5
waldo Member Join Date: May 2010 Location: DeWitt, IL Posts: 53	Re: Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? I can vouch for the fact that 4" stroke with Ford pistons will just kiss 8CM heads. I bought a swap meet engine, just out of the machine shop, and it was assembled as above. It had a wicked exhaust rap and lots of comp. Turning over with a wrench, it would lock up after half a revolution. Two Best gaskets with copper spray gave me a .055 clearance and a super running engine. Domed pistons with, now, Offy heads. I had to put .060 spacers under the plugs to keep the gap from closing up at high rpm. I ran this one in my H.A.M.B. HA/GR dragster last year and it held up fine. Going to run an old Bonneville engine this year.

06-19-2011, 11:15 PM	#6
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,882	Re: Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? Sponsored Links (Register now to hide all advertisements) This lowers the CR drastically. Why not have the heads redomed or get a new set of heads.

06-20-2011, 07:40 AM	#7
waldo Member Join Date: May 2010 Location: DeWitt, IL Posts: 53	Re: Ever swapped a 49 Merc crank into a 50 Merc and find it had more stroke? The .055 piston to head clearance gives good comp. The intake valves were closing the plug gap.