Having never rebuilt a bultaco I thought it might be prudent to ask some experts for any insight or advice..my recently acquired 27 is running pretty good right now but looking forward to a restore later in the year (hopefully after riding it this summer) .transmission seems fine and no undue low end noises so I'm hoping to just refresh top end, clutch and seals..compression is about 120..little low? Of course I realize that I'll know more when I get into it but thought id go ahead and start looking for some parts.. I've read where primary chains last and last...but should I go ahead and change it while I'm in there?

Thanks!

I usually check how much slack there is in the primary chain every time I take the cover off, and if you are even more risk-averse, they are pretty cheap to replace.

Beware of the primary chain tensioner falling apart and getting munched up. My M49 had a tensioner slipper that was a block of brass instead of the later type hard rubber wheel. I didn't like the look of it and just left the tensioner off and the bike has been fine. I think the mounting for the tensioner in the early 5 speed motors is different to later 5 speed motors too.

M27 clutch may be the early 5 speed type with segmented blocks of friction material on the friction plates. later 5 speed clutches were steel/steel and the basket is different. I suspect that it might be hard to get new plates to suit the old basket and hub if you need to. Can't remember if you need to replace the gearbox shaft to fit a later clutch. I'm thinking the old type clutch hubs drove on a key and the later ones have a spline

If it has done a lot of miles, the gearbox output shaft which is hollow and runs on the gearbox shaft using a sintered brass bush which might need attention.

I would start with a rod kit-crank shaft rebuild and work out from there. double check the ignition side where the crank bearing fits for wear. The last 4 Bultaco's I had rebuilt had bad ignition side bearing surfaces. I don't think Bultaco compensated for heat expansion and the left side bearing moved on the crank causing wear.

Ride the old girl and enjoy , if it has that kind of compression you have a good way to go before worrying about a rebuild.

Sherpa T's for the most part in this country don't really see a lot of hours as they aren't very comfortable to ride trails on.

 

It's pretty easy to check the mag side for any movement in the bearing, if the clutch works OK have fun, as stated earlier

the early 5 speeds used a key on the main shaft, the last m49 I built had same but it would accept Barnett plates same as

later engines so I am certainly not sure on m27.

The life of the Bulls is certainly dependent on maint. thru their lives, but it sounds like you have a winner.

 

I stripped down my M27 last year, new main bearings/ seals etc. Everything seemed fine after the rebuild. A couple of days later I noticed an oil leak. I traced this back to the final drive oil seal, or so I thought....had I forgotten to replace the skinny oil ring that goes on the sleeve gear? Nope. After close examination I spotted the cause of the leak. Oil was escaping past the flat bearing of the sleeve gear where the main shaft rotates. I pulled the engine apart again and was very surprised by the amount of wear on the end of the main shaft. I knew it would be bad as i was able to wobble the final drive sprocket with my hand. I replace the main shaft and made new flat bushes for the centre of the sleeve gear, problem solved. My advice would be to check this if you are going to strip down your engine.