Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties 45 belt drive

45 belt drive

Post Fri Aug 03, 2012 5:24 pm

Posts: 4
looking for any advice to help with instlation of belt drive.looking for input from those who have installed them.any tips or tricks would be very much appricated.
thanks steve

Post Sat Aug 04, 2012 10:07 pm

Posts: 391
A 45 is quite different than a Big Twin in that the transmission is basically in a fixed position so the majority of adjustment must come from tweaking the engine mounting to get good alignment. The belt needs to run true both in acceleration and deceleration modes and not crawl to either side.

Post Sun Aug 05, 2012 5:36 pm

Posts: 4
thanks for the reply robbie,i was leaning toward making the adjustments in the motor end of it.i cleaned up the channel that the transmission sets in and was able to get a little bit there and made a small adjustment on the motor and everything worked out.
thanks steve

Post Sun Aug 05, 2012 5:39 pm

Posts: 186
I run a belt on my 45. Can't remember what brand of conversion it is. May-be "Big Fix". I never had any alignment problems. It has always run true. I thought that I had the belt too tight. I took the time to check tension on a lot of automobile external timing belts. I now run it tensioned but NOT tight. Iv'e done 2500 miles on it, but can't comment on issues regards premature wear on the trans and engine bearings, that others have concerns about. I had problems with hard shifting, and managed to recitfy this by installing the (60) standard WLA ball bearings back into the clutch, and do away with the rollers. Rollers dont allow for lateral movement between the drum and hub like the standard balls do. There is a bit of drum wobble, when the clutch is disengaged, but belt seems to run true. I'm happy with the setup for now. Time and miles will tell.
Cheers Keith

Post Sun Aug 05, 2012 6:03 pm
Pa Site Admin

Posts: 5843
Location: Ohio USA

You got lucky Keith. Robbie's explanation mentions the fixed alignment issue which is the first critical part of good belt drive aligning. The other 45 transmission issues is hardly ever thought of though. No two 45 transmissions have the same clutch hub or clutch basket location specifications in regards to the transmission case and where the clutch basket sits in relation to the engine. The clutch gear determines that location and the clutch gear in all 45 transmissions never extends away from the transmission case the same distance. Depending on the parts, such as the clutch gear, the clutch gear roller bearing race, the clutch gear thrust bearing and it's race, and the machining of the case itself, determines how far out, or in, the clutch basket will be located at final assembly. I noted the clutch gear primarily because of all the critical machine work it incorporated on it. Even the spline work on the clutch gear has determining atributes to clutch basket location because it locates the clutch hub.

Post Sun Aug 05, 2012 7:08 pm

Posts: 186
I would have thought all clutch gears #2513-41 would have been manufactured the exact same dimensions. Same with the case. Same with the roller bearing and the thrust bearing. Hhmm!!! If that is in fact the case then, I would be looking at cutting out the tapered centre of the motor sprocket, and rewelding it up with the correct offset to match the clutch, if this can be done successfully. Just a thought.
The alignment, or positioning adjustment available with the motor, and trans, surely would be very very limited. Especially the motor. If the frame slots are not worn, and the correct locating dowels used, there should be no trans play available.
My motor pulley has like a disc on the inboard and outboard sides, so the belt doesn't run off. The clutch basket has a similar thing on the outboard side only.
My belt runs against the outboard side of the motor pulley. The nice squared edge of the new belt has now worn the corners off slightly, but the belt width still verniers up at 25mm exactly. Like I said, miles will tell. I'm expecting 40,000 miles from my setup. Hopefully!!
ps Is this topic regards fitment of the tin primary cover??

Post Mon Aug 06, 2012 8:58 am
Pa Site Admin

Posts: 5843
Location: Ohio USA

No two cases are alike. Nor are most of the other internal parts exactly alike. If they were alike, 45 transmissions would not have to be completely fitted throughout assembly. There would be no need for spacer sets on the mainshaft or on shifter fork assemblies. There would also be no need for roller bearing sets. Clutch gear roller bearing surfaces were held within .0005" on the diameters but shoulder lengths were not held as closely as roller bearing diameters. If all machining of cases and internals were exactly the same, assembly would be the only task in producing a 45 transmission.

Chain is forgiving and will run within a limited amount of descrepancy in location and it curves the differences between complete 45 transmission assemblies. belt drives need more precise alignment. The flanges on belt drive pullies are not intended to guide the belt. They are intended to keep the belt from jumping off of the pulleys during flex. If poor alignment causes the belt to use the pulley flanges as guides, the belt will wear out very quickly.

I like the idea you brought up for the sprocket modification in the taper. I am sure one could gain closer alignment with that fix as long as the move did not take away other needed clearances. The thought of modifying the taper sure beats the thought of modifying a frame.

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