Big Bore ate my clutch


Finally got my big bore installed; Je434 kit other mods are FCR39, Mrd/SSW and hotcams. I went to break it in using the mototune method and within 3 miles my clutch is mangled; slips like crazy. Is it common for a engine in this power range to overwhelm stock clutchs? Either way I need a new clutch, what do you guys recommend putting in the drz?

Stock Clutch will handle the power of the 440 as well as one of Eddie's strokers. Either your out of adjustment or you are using the wrong oil. Most go back with OEM clutch when the time comes to replace.

Is it common for a engine in this power range to overwhelm stock clutchs?

no,but if the clutch was tired or misadjusted it would die very quickly.

It has over 5,000 miles on it, using regular oil for breakin. I wouldn't know if it was misadjsted I never messed with it. Im sure its slipping because if I try to accelerate in 3th, 4th, 5th gear it revs but does not pick up much speed.

Forgot to say I have a hydraulic clutch system, it has very little play; perhaps that caused wear on the clutches and the bb kit finaly pushed it over the edge?

You have to pull the clutchh, measure the spring free length and fibers thickness to determine what the problem is. Then replace what is worn out.

Ok I can manage that, but I suppose you know what numbers im looking for by any chance.

Ok I can manage that, but I suppose you know what numbers im looking for by any chance.

As a matter of fact I do :thumbsup:

Clutch service and inspection In the FAQ

And to your original question, Nope, Not a big issue. Though some can smoke a clutch in one ride many get tons of use.

Some get way more hours then should be expected.

My 2003 , 4th motor build, 485cc, stroked bike has the Original clutch , and I too have a Magura Juice clutch.

Over 22000 miles on my M/T 436 kit clutch still great ! owe yes 38000 from new still on the original clutch :thumbsup: need to check your cable make sure it lubed and set up correctly. :ride:

So I checked everything out, pressure plate and basket are good. The springs all measured around 50.6mm. As for the friction plates I was a little confused and I need to clear something up. Do I measure with both claws of the caliper on a pad on both sides of the friction plate(around 3.00mm) or do I measure with one claw on a pad and on the other side with the claw on the aluminum?(around 2.5mm)

What I said may not have made since so here.

- = caliper claw

[ = pad

I = aluminum

1. -- was 3.0

2. -[i- was 2.5

Im thinking I do it the pad, aluminum way because the pads on either side of the plate do not line up and cannot measure the 1. way. Then again some of the pads on 2 of my plates were really close to lining up on either side and there was very little room to get a 2. measurement.

I hope I didnt confuse anyone and if this was in one of the pictures in the FAQ section I am sorry; but my computer wont load the pictures, Thanks.

From the picture in the FAQ it looks like the measurement is taken across the pads and his caliper is reading 3mm. If you're at 3mm you should be good, the FAQ says 2.62 minimum thickness.

Then if thats the case I dont know why its slipping; it shouldnt be my oil because I used the same oil prior to bb install with no slip.

Forgot to add I dont have a piece of glass to see if my drive plates are warped; but they do have shiny spots around the plates and duller spots in others instead of consistent wear.

Should I try to sand the drive plates lightly and try again?

Not entirely sure on how the magura set up works but i know that on most hydraulic clutch systems the fluid level in the master cylinder will rise as the clutch wears. Check your fluid level isn't to full as this would stop the clutch from adjusting itself as it wears, causing slip?

Just another thing to check

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