Project 'S', slight clutch problem.

[Muppet]

If you don't already know, I've fitted an 1100 'S' engine into my 1100GS. Actually had it out for a run today, after dicking around with different fuel injectors and the like it's now running rather well. Apart from the clutch that is.....

When it gets hot, the clutch lever gets heavier and heavier (or perhaps stickier should be the word) and then when I disengage the clutch it sticks open (lever back to the bar) and presto....no drive. It's stuck fully disengaged. Let me explain what I've done.

1100 S engine fitted with 1100 GS flywheel & clutch. The GS is bigger diameter than the S and different flywheel (heavier I imagine). It was a straight swap. Gearbox is my GS 5 speed, bolted straight on. When the boke is cold the clutch works fine, within about 10 minutes or less, even out on the open road, it starts to stick and eventually sticks completely.

What I think is happening....
I've got the exhaust headers and cat from the S engine, and then a single straight through silencer from the cat. It's loud but not too bad. I think the heat build up from the cat, which is mounted close to and directly underneath the gearbox is causing the clutch push rod that goes through the gearbox to expand and stick. Or the hole it runs through in the shaft is getting smaller. Letting it cool down for 10 minutes or so allows the rod to move and I can then ride off again, but it soon starts to stick. Does that sound feasible?

I can try putting some kind of heatshield round the cat to see if that alleviates or slows down the problem, and if it does I'll have to go for a set of 1150 headers with a Y piece and silencer. This cat really does get bloody hot, way hotter than the original one yet the engine temp seems fine.

Your thoughts please Gents.

 

[russ996duke]

it may well be the heat from the cat....or it might be that the pushrod clearance is too tight to start with, and "normal heat range" it has to work within means that expansion closes up all the tolerance and more.... have you compared push rod lengths GS to S?
good luck with the project anyway, it sound fascinating

 

[ktmmark]

Don't think it will be the exhaust heat .I would make sure it's the push rod thats tight first & not cable or arme etc .Then make sure the push rod is clean & not bent ( is the rod the one with the thin section for the felt )

 

[Schtum]

Dave says.....

His sticky-pushrod theory sounds very feasible, but requires the "wrong"
push-rod to have been fitted. Which one did he use, the GS one or the S
one? Here are a couple of other theories:

A - The clutch fluid is getting too hot, maybe even boiling, and the
slave cylinder is expanding and operating the clutch. However I'd expect
the lever to but solid then, not flop back to the bar. -

B - He's used the wrong master cylinder and/or slave cylinder and
therefore A is happening even though the fluid isn't getting that hot.
Which slave & master are in use? (I'd still expect a solid lever though)

C - The Clutch itself has a problem. Warped pressure plate is most likely
to cause the symptoms described and may well be OK when cool, just look at
the difference in my Transit clutch hot/cold before I changed it.

Whatever is wrong, and exhaust swap/heat shield is treating/masking the
symptoms, not the disease. He needs to get to the root cause of the
problem and fix it. If the pushrod is the problem (It is straight, isn't
it? - A bent one will easily cause this!) then simply swapping it for the
other one should fix the problem. A quick measure of both rods will show
which is the smaller diameter - use that one. It can't be "the hole in the
shaft getting smaller" 'cos only water gets smaller with heat.

Tell him to mail me, give him this address.

 

[Muppet]

Thanks fro the replys, to expand further...

The gearbox is the original one that worked fine with the normal engine. The pushrod is the same, the clutch is the same, everything is the same except the engine and exhaust system.

Although I didn't renew the clutch when I swapped it, with the flywheel, from the nromal engine to the S engine, it had only done about 6,000 miles, so should be fine.

Mike, I'll mail Dave but his first 2 points are irrelevant as it's a cable clutch.