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scat crank issues

Posted: Wed Apr 17, 2019 7:57 am
by kenhaverhill
has anyone run into issues with thrust and a scat crank? I have done engine work with stock cranks with no issues , installing a scat crank for the first time in a 26. block has new babbit,line bored and radius cut on babbit ends. when crank is dropped into block 3rd main journal has no clearance in block ,no in or out thrust .third cap has almost all thrust surface removed and still will not fit onto crank . almost seems as though journal of crank is to narrow? there is a shoulder on both sides of crank journal which sits off of counter weight. I am missing something? even if babbit was removed from block all together crank would still be tight fit into third bearing saddle of block. thanks ahead of time

Re: scat crank issues

Posted: Wed Apr 17, 2019 9:45 am
by Adam
There’s something missing from your post. Measurements should tell you everything you need to know.

A stock block has no babbitt thrust. The only thrust is on the cap. If you want thrust in the block, you have to mill some iron off the front and rear of the third main saddle before you babbitt.

The radius on the scat cranks is a little bigger than the stock Ford radius, (by maybe 1/64” if I remember correctly) so if you are using too small a radius, the crank could be hanging up on the radiuses.

Are you babbitting and line boring this yourself, and have you done this before, or did you have a shop do it to specifications, but without the crankshaft actually there?

Re: scat crank issues

Posted: Wed Apr 17, 2019 10:53 am
by John.Zibell
kenhaverhill wrote:
Wed Apr 17, 2019 7:57 am
has anyone run into issues with thrust and a scat crank? I have done engine work with stock cranks with no issues , installing a scat crank for the first time in a 26. block has new babbit,line bored and radius cut on babbit ends. when crank is dropped into block 3rd main journal has no clearance in block ,no in or out thrust .third cap has almost all thrust surface removed and still will not fit onto crank . almost seems as though journal of crank is to narrow? there is a shoulder on both sides of crank journal which sits off of counter weight. I am missing something? even if babbit was removed from block all together crank would still be tight fit into third bearing saddle of block. thanks ahead of time

You will also have to modify the "horseshoe" for the pan inspection cover. Usually with the rear one you cut out a section for clearance, then weld the legs to the other horseshoe.

Re: scat crank issues

Posted: Wed Apr 17, 2019 12:12 pm
by kenhaverhill
I spoke with the people at scat and they tell me that they have made some changes including a much bigger radius , they feel that even though it looks like enough I still need more radius ground into babbit in block.

Re: scat crank issues

Posted: Wed Apr 17, 2019 1:34 pm
by Adam
kenhaverhill wrote:
Wed Apr 17, 2019 12:12 pm
I spoke with the people at scat and they tell me that they have made some changes including a much bigger radius , they feel that even though it looks like enough I still need more radius ground into babbit in block.
Did they tell you what the “new” radius is that they are grinding on the cranks?

Re: scat crank issues

Posted: Wed Apr 17, 2019 3:54 pm
by Kohnke Rebabbitting
Of all the scat cranks we used, 3 were about .052 to short, in the rear main, the flange was thicker also, so Vern opened them up. These came out of older production, I called them at that time, and made them aware. It was cheaper to fix, and had control on the fix, them send them back.

We always check New, or reground cranks before we even think about babbitt.

Anyway, when the crank was set, the center main had equal distance on either side, and the time gear on the crank was .010 short, of flush, to the cam gear, in length.

The rear cap, normally has more babbitt on the front of the rear main, then the back, because of front thrust wear.

Always punch the oil holes out, clean with a drill, at the last.

Herm.