Monobloc slides - they don’t!

I’ve stripped and cleaned my 389 monoblocs in my ultrasonic cleaner, and they’ve come up rather nicely for 60 years old.

On reassembling them I’ve noticed the slides don’t. They stick. I was not aware of their condition prior to the strip down as the cables and twistgrip were very poor and have been replaced with new.

There is evidence of scoring up and down the slides - will a session on the polishing wheel sort them out or cause further problems? I don’t really want to replace them if the issue is elsewhere within the bodies. I didn’t remove the internal choke from the body - should I?

Do they bind near the top? I have a pair (389/689) for my N15CS, got them cheap so there is no big loss if I can't make them work. They slide fine once in but bind close to the top. It may be out of the working range, and I'm still checking it out. I have read that overtightening them can warp the body, causing binding, but my flanges are flat and it doesn't seem that overtightening should affect the top. I wet sanded a bit with 1000 grit and used some rouge on a Dremel. They're better, but still not free throughout. I read some people squeeze the bodies with pliers but that technique seems to be hit or miss and it may turn out worse. I would lean away from the scoring and toward 'out of round' based on what I'm experiencing. I wish I had a good tool to gauge them but I don't. Yet.

Did you refit the slides back in the carb' they came out of? Your picture suggests you didn't as all parts seem mixed up. I always keep parts for each carb together, particularly moving parts. Have you tried swapping the slides over?

When I got new (hard anodised) slides for my 650ss monoblocs they wouldn't fit.
Measured the bores for the slides and they were oval.
A bit of judicious repeated squeezing (vise & balsa wood pads) they became round again. The new slides then fitted with no play at all!
Worth a check.
Cheers
Rob

robs ss said:

When I got new (hard anodised) slides for my 650ss monoblocs they wouldn't fit.
Measured the bores for the slides and they were oval.
A bit of judicious repeated squeezing (vise & balsa wood pads) they became round again. The new slides then fitted with no play at all!
Worth a check.
Cheers
Rob my

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Were they oval near the top or throughout? I have 3 carb bodies and all are just a bit tight at the top, and I can't see why it would distort there only, unless it's tightening the ring perhaps. I'm leery of squeezing them, not that it's a bad method, just not sure I trust myself. I could try on the 'spare'.

Flatspot said:

I’ve stripped and cleaned my 389 monoblocs in my ultrasonic cleaner, and they’ve come up rather nicely for 60 years old.

On reassembling them I’ve noticed the slides don’t. They stick. I was not aware of their condition prior to the strip down as the cables and twistgrip were very poor and have been replaced with new.

There is evidence of scoring up and down the slides - will a session on the polishing wheel sort them out or cause further problems? I don’t really want to replace them if the issue is elsewhere within the bodies. I didn’t remove the internal choke from the body - should I?View attachment 113624

Click to expand...

Sticking at the top - very typical. That means you'll only be in trouble if you twist the throttle "too much".

How much is too much? The carbs will let you know!

Carefully determine the sticking points and massage them out. best done with the flanges bolted to the head.

Turn down a wooden dowel to use as a drift.

Finally, albeit 2 months late in reporting as we’ve been touring Scandinavia for the past 7 weeks, I fully stripped the carb bodies including removing the main innards. Then gave it all another good clean up and removed any scratches with a good polish. Reassembled and everything slides nicely.