Engine recon - crankshaft cracks - one for Roger !

[Geko]

People, the long overdue recon of the 4A engine is finally moving forward. It's all stripped down and i'm inspecting the faults. The ugly finding is the meltdown of the cyl 1 conrod bearings and ensuing damages. The piston head was hitting the head gasket causing it to shred, no big deal though. More worrisome is the poor shape of the crankshaft which would require serious grinding and of course ... one crack. My concern is that the crack is longitudinal and located smack in-line with the casting "join" (white paint lines). Cause for concern?

 

cheers

[Nick Jones]

The crankshaft is a forging not a casting, but will show a line of "flash" where the dies meet not unlike a casting. Possibly the line/crack is related to the original process and if so it's probably not an issue. However, definitely worth getting it properly crack tested before spending anything else on it. Magnetic particle inspection (MPI) "magnafluxing" is the normal method for cranks I think.

 

Cracks that run circumferentialy around the journal, usually right by the fillet radius are the ones that mean the crank is scrap and are not uncommon on the dry liner 4s and 6s.

 

Bearings are impressively distressed - presumably it was making scary noises?

 

Nick

[RogerH]

Hi Stef,

it does look cracklike but my feeling is it is not a crack. There are no forces in that plane therefore nothing to make it crack.

However the only sure way of knowing is get it crack tested. As Nick states use a magnetic particle test (often referred to as Magnaflux).

Most engine shops do this process.

 

Quite often when an engine has sat for a while the gap between the bearing shells produces a 'dirt' line on the journal.

 

And just to clarify ALL the four pot cranks are CAST. Forging of cranks went out many years ago (1930's).

It is called 'Green sand casting' and invented by Ford.

 

Roger

[Motorsport Mickey]

+1 with Roger, on cracks ...he da man.

 

I've built nearly 2 dozen 4 pots and I got to tell you I've NEVER seen a longitudinal crack, that's a stain or other surface imperfection. More of interest is why the piston crowns are touching the copper composite gasket ? is the gasket a 1993cc size on a 2186cc bore ? therebye sticking into the bore dia and burning.

On a "cooking " engine on a composite gasket I'd run a 40thou deck height for the piston (down from the top of the liner, not the block) obviously the correct size gasket for the piston. Don't worry about grinding the crank to scarily small sizes, I won my last TR Register championship on a crank deliberately ground to -60 thou (really) on the big ends running Massey Fergueson bearings.

 

Mick Richards

Edited June 26, 2017 by Motorsport Mickey