Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Rod bearings

Rod bearings

Post Mon Feb 19, 2018 5:20 pm

Posts: 569
Location: Wa, USA
The rod bearing saga continues.

I bought a bore gauge and an Eastern lapping arbor and got the races lapped round. It went better than I hoped for a first try. I ordered the right size of rollers and a new set of steel cages from V-Twin, hoping that they were Eastern parts since that was the only place I could get the Eastern lapping arbor. Of course they weren't. Out of round and some of the rollers had to be forced in as the fingers were not straight. Got an NOS set from Ebay.

Today I put everything together dry and torqued the wheels together. Rod side to side clearance is .032". What are the pros and cons of just leaving it that way?

Post Mon Feb 19, 2018 6:50 pm

Posts: 170
Location: Carver, MN

IMO, .032" rod end play is not anything to loose sleep over. Often consulting later model service manuals can be enlightening. In a '69 manual the rod end play is listed as .006 to .010, but by '90 the spec was .005 to .025 with a service wear limit of "exceeding .030." Of course one always needs to consider whether the spec changed because of a change in the parts used, or because the factory realized that the extra clearance cause no problems (or like in the case of Twin Cam pinion shaft run out, they just were not willing to fix the underlying design flaw). Trouble is, they seldom explain changes in published specs. The S&S stroker instruction sheets, at least through the '80s, said this and I quote: "If rod side play is more than .035" try a different crankpin. We have run side play of as much as .045" without serious consequences." end quote.

Post Mon Feb 19, 2018 7:27 pm

Posts: 569
Location: Wa, USA
Thanks, Lee. I was thinking along the same lines myself. I have the Victory 80 performance books and the recommendation in them is .010 to .020 for hard running and .030 for strokers. I do not have a stroker, but once broken in, I do tend to run the wee out of them.

Post Wed Feb 28, 2018 1:49 pm

Posts: 19
Hello Woody,

It's essential that the bores in the forked rod has the same diameter.
Also check rods for straightness .
Decks on the engine block need to be square as the cylinder base.
Any of these things not correct you will get side forces on the rod big end.
Did you get the gaskets ?

Post Wed Feb 28, 2018 8:36 pm

Posts: 569
Location: Wa, USA

The gaskets have not arrived, yet. I will email you when they get here. The rod bores are all the same size now. The rods were straight when assembled. The deck surfaces are square to the case bores. The old cylinders were faced square to the bores. I am putting new ACF cylinders on it so time will tell.

Since my motor ate some cam shims I need to disassemble the oil pump I got from you for cleaning and inspection. Are there any settings and adjustments that I need to know about?


Return to Big Twin Flatties