I am in the midpoint of a 3-speed motor rebuild, had about 5k on the speedo when disassembled. I have it apart, it is apparent it will get a cylinder honing, new piston and rings, points, condenser and cam assembly.

My question is this: What are the typical wear items or weak spots in the internals? I plan on replacing all of the above along with clutch plates. For you rebuilders with lots of experience, are there any other things that should be replaced while I am in there (even if they look good on inspection?) I am thinking of historical weak points in the engine etc. For example, the oil spinner looks fine, should it be replaced anyway? Any tips appreciated, thanks!

You'll need to take a good look at the valves too, at the very least a valve grind is in order. Also take a good look at the shift forks and the pins that hold the forks to the shift drum, these have a tendacy to wear after 30 + years and thousands of shifts too. Also I would replace the oil pump for peace of mind knowing a new one would likely last our lifetime! LOL

Brian

cam chain tension should be checked,there are alot of little parts,cam chain,sprocket and tensioner ''rubber wheels'' in the jug,and under the stator cover that can wear out.

Thanks for the responses - I should have clarified in the initial post, am replacing the entire cam chain assembly - including the little plastic rollers, sprocket, tensioner. But was not going to replace the cam itself.

i would change to one step bigger cam,the dr atv oem honda hot cam.they were in SL70's.it should give you a slight boost with even a otherwise stock build.

I like the SL cams, nice power band, noticeable improvement. If your going to add a 88cc cyl. and piston with your build you might add the heavier clutch springs too.





Grant

69 KO Saphire Blue all stock
70 HKO Emerald Green 88cc
71 HKO Blue Green 160cc
70 HKO mutt Pile-O-Parts
09 Harley XR1200

This cam: BEARING_TYPE RACE_CAM Z50_TO_1981 ATC70_ALL CT70_TO_1981 PASSPORT_80/81 TRX70_ALL XL70_SL70_CL70
Or this one: *HOT_CAM OEM_HONDA FOR_Z50A'S AND_CT70'S THRU_1981 (82F)

This will be standard bore, not an 88. I don't mind trying one of these cams though, if you guys think it's worthwhile and the improvements are real and noticeable...

do not use the bearing cam.its too much for a stock build too.they cause problems on old style heads also.they suck.i know first hand.use the oem style non bearing honda hot cam or the mini monster cam.these two are ok for a cam only upgrade,yes you can feel the difference and the bike sounds cool idling.

I wouldn't use that cam. I've tried them twice a stock 70 doesn't have enough comp. to . make for the soft bottom end and you have to scream the s%$# out to get anything. its a little better on a 88cc with an after market head, but the sl cam runs better IMO. plus the 2 bearing cams I tried were solf and ate rocker arms too.


Grant

69 KO Saphire Blue all stock
70 HKO Emerald Green 88cc
71 HKO Blue Green 160cc
70 HKO mutt Pile-O-Parts
09 Harley XR1200

P.C. and Grant are right. The bearing type race cam is a dog at lower RPM's. No grunt whatsoever. All it want's to do is screeeam.