Isolastic Play

Found I had a very noticeable total engine vibration around 2000-ish RPM like it's trying to jump out of the cradle. I checked the front iso's and I can physically move the engine from side to side about 1/16 inch. The rears are tight. Is this normal side to side play or do I need to shim it? I tried a search but that feature kept crapping out on me and I gave up. Are there any threads on this subject or can somebody let me know if this is normal? I didn't install them originally so I do not know how they may be shimmed already.

Thanks.

Scott

It pays to tick the 'Using Google Search box when you use the site search top of the page.

https://www.google.com/search?sitesearc ... isolastics

There should be plenty of info in the link above.
'When I got my Mk2a the PO went on about how good the handling was etc,when you grabbed the back wheel you could get a clunk from the clutch cover hitting the Z plate,due to not only the rear isolastic but the stud through it was not that tight,the rear tyre was almost square, he must have dismounted and pushed the bike around each corner he came to.

I've ridden one with 1/4"+ slap slack at front and at least that in swingarm and it was a smooth operator engine vibration wise. Too tight iso's vibe way more than loose clapped out ones though the hinged handling onsets easier with looser isolastics. So check head steady and cradle and other things for fouling between frame and engine. It may be symptom of something big and bad getting loose, so peek in primary too. At low-ish rpm I've had electrical spark drop outs that made rough feeling that cleared up with higher vibes keeping the bad connections working better.

Re: Isolastic Playp

Hey Hobot, what kind of meds are you on?? I have a very bad neck & back injury & I still can't decifer ALL your speak.. Love it, just don't get it I and I stopped meds a long time ago!! Perhaps I should start again

1/16 is not normal, five-ten thou.

kernel65 said:

Found I had a very noticeable total engine vibration around 2000-ish RPM like it's trying to jump out of the cradle. I checked the front iso's and I can physically move the engine from side to side about 1/16 inch. The rears are tight. Is this normal side to side play or do I need to shim it? I tried a search but that feature kept crapping out on me and I gave up. Are there any threads on this subject or can somebody let me know if this is normal? I didn't install them originally so I do not know how they may be shimmed already.

Thanks.

Scott

Click to expand...

Yes, 1/16" is WAAAY to much clearance. But ... "five-ten thou" (.0005)?

Holy Moly, I don't have anything that could even measure that in this application!

I find that .006" works quite well for me.

Thanks for the replies.

From what I understand and read, I can pull and shim the front iso's mounted on the bike by supporting the engine and pulling the bolt, correct?

Can I make shims or do I need to order them special?

Scott

" I can pull and shim the front iso's mounted on the bike by supporting the engine and pulling the bolt, correct?

Yes. If you are pulling the entire unit that's correct. If you are just adjusting the iso clearance you don't really need to pull the bolt all the way out, just enough to insert shims in one side. There is no need to shim equally on both sides though I have to admit I do that - at least as close as is possible.

Order the necessary shims - get a selection of various sizes. Old Britts has them, as well as all the other iso parts if you are refurbishing the complete assembly.

If you get the Hemmings adjusters, it's much easier. You can also get the later style vernier adjusters, but it depends on which year your bike is, Hemmings works on them all and doesn't need shims. Yes, you can pull the front one out and work it on the bench, the rear is not so easy, but I installed Hemmings adjuster on my S without taking things completely apart. Getting the boots on is another issue. I never found much of a difference in the way things work from .005 to .01 on either set. YMMV. If you want to do the shims, any Norton dealer has them.

http://www.members.shaw.ca/randell/ Bottom of the page under isolastics

Dave

Thanks guys, appreciate the help.

1. Worn ridiculously wide gaps do not transmit vibes more, they smooth it.
2. Worn wide iso gaps can make handling more dangerous, not enhance vibes.
3. Softer cushions lower isolation rpm threshold to isolate.
4. Harder cushions raise rpm isolation threshold.
5. IF both front and rear isolastics gaps very wide and the swingarm loose over 3/8" at tire patch its possible with worn sleeve shaft bushes, that drive chain and primary chains tug & flop can skew cradle in iso mounts to touch metal to metal for cyclic waves of obnoxious vibration at low rpm, but more likely to onset annoyance level wobble just going straight and easy legal speed on steady throttle with maybe vibration sense of buzz in waves rather than constant throbbing vibrations.
6. Too low tire pressure make vibes felt more while harder aired tires smooth out better.
7. With enough out of spec faults listed the head steady can be put in a bind to add low rpm vibe discomfort.
8. Check for frame or cradle cracks just in case.

Thanks for the checklist Steve. Time to order some shims...

Its NOT ' play ' . it's C L E A R A N C E : nominally 10 thou. some say 2 to 5 thou . Wots This HALF an INCH ! :shock: :x