Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Some UL engine specs needed...

Some UL engine specs needed...

Post Tue Nov 29, 2005 9:16 am

Posts: 1
Need piston to cylinder clearance as well as tourque for cylinder base nuts and head bolts, alum. heads. Thanks

Post Tue Nov 29, 2005 11:45 am

Posts: 646
Location: Detroit
Take a look in the knucklehead manual for UL specs. However, as far as I know there are no base nut specs set forth. We had that argument here some months ago. The book says "tight," but obviously not "too tight" because the studs are set in aluminum and can pull out. Since 1972 I have never torqued base nuts to any particular foot pound rating and never had a problem that I know of. Others here will tell you that only a lunatic would use such "barnyard methods." Oh, well, . . . .

The fact is I could tell you the headbolt and piston specs but you will gain far more knowledge from having to peruse the manual and coming across a wealth of other information at the same time than you will get from just someone spitting the basic numbers alone at you. In other words, cheat and read the book. If you don't have the book or can't get one (and no one else does this for you) I will post the specs in a day or so.
New Knuckleheads? Thank, you, Jesus!!

Post Wed Nov 30, 2005 7:18 pm

Posts: 514
I agree with Loop, use your wrench and get those base nuts good and tight, even a dab a locktite won't hurt ( the red) just check after the first 200 miles and won't hurt to check every 500 miles after that, but probably won't come loose, Now as far as the clearence is we run the gamant around here from
.002 as far as .004 to even .005 these flatty swell up when they get hot, remember no top end oil on these bad boys. Do you want her to lock up?
how lucky do you feel.

Post Wed Nov 30, 2005 8:19 pm

Posts: 646
Location: Detroit
Here is what the 1940 - 1947 manual says:

Pistons for 74 & 80 SV

(paraphrase) For oversize, add stock cylinder bore to the oversize needed. This gives the exact size to which the cylinder should be refinished. Check your work carefully. If you did it accurately oversize pistons furnished in various oversteps will fit with normal clearance. . . . . When jugs must be rebored beyond .070 oversize to clean up replace with new ones. Page 46 for SV.

This isn't much help if today you have pistons from Hong Kong Wong, but once again the manual saves the day:

(paraphrase) Oversize pistons come in .005+ .010+ .020 etc . . . .070+ ---.001 to .002 clearance in cylinder. Page 75 Illustration 61 Piston for 74 and 80 model SV.


(paraphrase) OHV and SV: Use new gaskets every time unless you only have the old ones which will most likely leak. Coat gaskets with light coat or oil or grease on both sides. Bolts must be tightened evenly to attain a tight joint. First turn bolts just snug; then tighten each of them 1/8 to 1/4 turn at a time until all are securely tightened. Use special headbolt wrench. Pages 86 - 87.

OHV: use flat washers on headbolts.

SV: use flat washers on headbolts for iron heads and use convex washers on headbolts for aluminum heads. (They aren't kidding here, flat washers can crack aluminum heads.

The torque spec for heads in this manual is "tight" so there is no foot pounds spec given. I always used 65 torqued foot pounds and that worked just fine for both Knuckles and U series.

You still need to buy a manual which costs a little less than $20---cheap and invaluable for the information it contains. What I put up here for you is really bare bones.
New Knuckleheads? Thank, you, Jesus!!

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