SQ4 crankcase inline boring

[xavier.devars]

Dear fellow Arielists,

This is a fairly common topic for square fours, but here is my story : I left my bottom end with new bearings to ream and cranks to my usual shop, with the instructions of line boring to max 5/100 mm radial play, and they returned it with bearings reamed to 12/100, as the cranks were binding up to this clearance and they turned out not to be able to do it properly in line. Even with a Morgo oil pump, I don’t think it will do.
Is there any way to ream these manually, using a proper made jig, with an expandable reamer for instance ? After a quick search, I wasn’t able to find a proper shop here in France.

Kind regards

Xavier

[nevhunter]

I don't think you will get the accuracy or finish with an adjustable reamer. The best is a fine point single cutter run at the correct speed with a very fine feed lined up on centre with the bearing on the other side.. There are align boring machines but a later mill or good larger lathe will do it with a good operator. Are the bearings Babbit or Copper lead or alutin?. Your original clearance specified is OK for Babbit. The other two need more clearance. About what you have though the alignment is suspect. Nev

[xavier.devars]

Thanks Nev, the bushes are from Dragonfly, I assume these are babbit, but should ask for more details.

[Paul_Linden]

There was a post on this forum of someone who did this in their home workshop. It had pictures of the set up. I think it was posted by Paul Wirdnam.