Isolastic / engine mount problem.

Have nearly completed the pull down, can not pull the bolts out of the isolastic, I have not been heavy handed with them, yet......

Any suggestion on how to get the units apart, grind off the heads and push ?, heat ?, cold ?.



Is this nut supposed to be there ?.


Thanks for the advice.

Dang, I though I could just chime in to get ya going but got a double take on the thick rusty nut spacer. No its not supposed to be there, but I didn't think the space for it would be either. My 2 750's only had room for the shim factory shim stack between frame and the wide slip washers or for the adjustable upgrades. My 1st thought is someone milled down LH cradle tube.

Anywho nothing should be holding the long through bolts inside but grime and rust or they are bent some how. Can't really get heat through the the rubber doughnuts to reach the inner tube the bolt slides through. Looks like a job for both a puller on one side and 3 lb sludge on wood block or sacrificial nut to protect threads, if the long bolts are worth saving once extracted. Maybe lock two nuts on end twist bolt to free it, though risks trapping a nut on bolt you can't grip bolt spining to get em off. I have heard of a few that had to saw ends off to remove cradle to bash out the whole rubber complex and start back anew.
A real man's sport hobby to get past hang ups and only destroy the minimal, when really want the relief to crush the whole thing.

In the end if ya live long enough its a project you'll savor for what it took.

Cut em and buy new axles since the originals look tired. I'm also unsure what is up with that rusty nut.

Looks pretty frozen, and that rusty nut is wrong. Before any bashing try soaking with WD40 or CRC etc' for a day or two and then slip a tube over the Iso stud and with a big washer over the end fit the nut and wind it down as an extractor. It might break the rust "freeze" and pull the stud. If not, they have been hacksawed off and then pressed out in a bench vice.

Mick

No matter how you get it apart, MEASURE THE FRAME!!!!! Also, ask the Forum if ALL rear engine mounts are the same WIDTH and what that width should be. You may have a bigger problem then a frozen iso.

A few days of penetrating oil, then some heatings and coolings of that central bolt, will be helpful. Get the effer nice and hot. Then let it cool. That should break some of the internal corrosion free (yes it may melt a few rubber donuts, but that seal will be easily broken). I agree, you're probably best off buying a new bolt for reinstallation.

That extra nut freaks me out. When I removed my front ISO to install Mk III adjustables, I had a devil of a time getting it back in there, WITHOUT an extra nut. No way I could've fit that in there.

As a previous poster has suggested, you may have frame issues. Here's hoping NOT.

Best of luck.

I just measured my '72 frame. Side to side at the outside of the gussets the rear isolastic bolts through is 9.25 inches. My guess is your's is a bit more due to that "rusty nut." This is also where the battery box mounts, so unlike that will fit in there. Definitely get the frame measured before moving ahead.

The manual has it at 221.99mm to 222.50mm between the plates. The left side collar looks original so the there's some serious alteration activity there. In any case, the rear studs are cheap. it might be sawzall time.

Josh Cox. You have my curiosity going on this one. Please let us know what you have found out about the frame and cradle.

Just a picture of the right side iso explain a lot.

G'day Gents,

Thanks for the input, am away with work for a few days so will not be able to measure until tuesday night,,,, work, again getting in the way of my far more important hobbies.

The RH mount looks unmolested, I'll replace all the bits, due partly to my extreme prejudice in removing said items with an angle grinder and mallet, the bolts were corroded into the inner tubes and bushes .

I would appreciate the measurements of the OD of the cradle bracket........., so I can measure both, I believe they will be OK, but its best to check.

Rear frame iso plates are: 8.740" to 8.760" or 221.99mm to 222.50mm I do not know how wide the rear cradle should be, but when all the bits are assembled, there should be very little play or interference. I would be concerned about a PO "realigning" the engine. Things can be fairly tight in that area and people might want to "fudge".

If you can get pictures and measurements, there are many people several forum pay grades above me who can decipher this.

I wouldn't put it back together until your sure.

Remember the old adage, "change one thing, change everything".

Good luck, down under.

My Clymer's book shows the dimensions between the front iso plates, but not the rear. If you want the rest of the dimensions, I can post or email them. I can't verify the accuracy, but everything on my 69 was within spec as near as I could measure with the Clymer's.

Dave
69S

I used the '73 workshop manual. Good pic of the frame layout.

Am I able to install the newer model systems into the frame without modification ?, the MK111 Vernier system ?, with the same frame and cradle ?.

DogT, those measurements would be great, Joshua_Cox1@westnet.com.au or post here.

P.S. when I pulled the drive side inner case off the bike, there was a 3/8 nut being used as a spacer between the centre bolt and the inner case, certain that nut also does not belong.

750's rear cradle iso tube should be 6 5/8" or 169 mm wide.
I have an excess steel 750 cradle if worse comes to that.

The center bolt of 750 inner cases should only have thin shims/washer between the hex center of mount bolt and back side of case. Mount inner case on crankcase with the gasket and 3 bolts lightly snugged up then just add spacers to match on bolt hex base w/o strain on the case when nipped up.
I like to put studs in place of those 3 little bolts as crank case don't drool on me with primary off and easier to remount putting nuts on studs than bolt in aligned holes. Small comfort/convenience only, not a big deal.

Save the big old doughnuts as its worth while to add extra to the rear isolastic.
I just slit my old ones to stuff in as the tube holds them together. Less sag over time and does not add vibration as its only a pivot in rear, the bouncing is at front.

Do check the face to face evenness of the frame rear mount plates, bend and bash as needed to get them parellel as possible for no bind on dialing in the iso gap later. Fame can be tweaked a good bit and not matter a whit to ride wild as ya like, long as just it assembles w/o much or any forcing, good to go.
Swing arm is another matter and should also be square and backed up by the late Hienz Kulger collars. I put in grease zerks through swing arm bushes to eliminate the oil drool to dry once a season and preserve it for future generations, as seals out moisture the missing oil will not over time, if your mount ever sets up long again w/o ya constant attentions.

All measures up nicely, thanks.

The previous owner had modified one of the stud collars.

To answer your question about converting to mk3 iso's I believe the rear will fit, but you'll have to cut down or buy a new front mount to fit. Lots of info in the search function on this.

Josh, before you get the MkIII kit take a look at Mick Hemmings's adjustable collars. I've used both and the MkIII's have some drawbacks. It looks like the nut was mated to the other collar from the pic's but all that matters is that you go back to stock and it comes out right.

Josh Cox said:

Click to expand...

Josh Cox said:

Click to expand...

Maybe in past the slice off was done to shift power unit chain over for wider tire.
Other things like gear box would also need trimming but may of been replaced before you got into it.

On adjustable's I mount the holed adjuster on RH at front and LH at rear for access.
Had to flip mine over once to be able reach adjusters, after fully assembled to find out about that detail. I strap couple of wrenches on and adjuster pick to fiddle them on the road till best comprise on un rear linked and rear linked Commandos.
Its sorta like tuning a guitar, adjust one end and throws tune out the other end.
Part of the fun of such simple ole Commando craft.