isolastics

brxpb · May 19, 2017

In all the time I've had my commando I've always adjusted all the isos to the same clearance, which set me thinking, which iso affects the smoothness of the ride the most, can you even run different clearances on front top and rear? The dave taylor head steady would suggest you could keep tight head steady clearences with the other two running bigger.
I've always run mine pretty tight but now as my arse is nearing 50 I'm looking for more comfort, less vibes, any experts?
Paul.

RoadScholar · May 19, 2017

Have you re-bushed your ISOs lately? If you have then the standard settings (shims or vernier) should smooth out the vibs between, say 2700 and almost 4000 RPM. If your ISOs are original factory, as in 40+ years old, then all bets are off.

The ISO internals don't live forever; I'd venture to say they may be good for, maybe 10 years; they bear weight no matter how you park or ride your mount. The Mk3 model made an attempt to bear some of the engines weight with the spring going from the headsteady to the frame. One of the forum members' (Comnos) demonstrated a modification where he installed a valve spring under the engine, between it and the frame, good stuff.

Fullauto · May 19, 2017

You'll also find the modern compounds used are somewhat more forgiving. During the rebuild, new isos from Andover Norton were fitted (14,000 miles ago) and I don't get the usual shakes down low which were a fact of life. Mine is commendably smooth right through the range with minor patches of vibes through the pegs or bars at various revs, but nothing bothersome at all. From 60 until at least 80mph it is impressively smooth. Much better than I remember it from the old days. I have a 22 tooth gearbox sprocket, so that changes the speeds at which vibes are felt.

aceaceca · May 19, 2017

I have always thought it was unwise to stiffen up the head steady. I run my 71 commando on all original iso's except newer pucks on the head steady. My reason is this. If you stiffen up the head steady you are loading forces onto the top of the cylinder which has a large moment arm due to it's height. You are putting forces on there that are not meant to be. The large fore and aft isolastics are supposed to bear the brunt of the loads and smooth out the ride. Which they do. My bike is smooth as silk at most revs. I am also hesitant to put new isolastics in there because of the stories I hear about the smoothness being ruined with new harder pucks. It is the same story in cars. People stiffen the suspension and shocks up so much that the car may go around corners quickly but it rattles you spine and false teeth in normal driving mode. I am staying on the smooth side with my ride. Pick your own pleasure though.

Fullauto · May 19, 2017

aceaceca said:
I have always thought it was unwise to stiffen up the head steady. I run my 71 commando on all original iso's except newer pucks on the head steady. My reason is this. If you stiffen up the head steady you are loading forces onto the top of the cylinder which has a large moment arm due to it's height. You are putting forces on there that are not meant to be. The large fore and aft isolastics are supposed to bear the brunt of the loads and smooth out the ride. Which they do. My bike is smooth as silk at most revs. I am also hesitant to put new isolastics in there because of the stories I hear about the smoothness being ruined with new harder pucks. It is the same story in cars. People stiffen the suspension and shocks up so much that the car may go around corners quickly but it rattles you spine and false teeth in normal driving mode. I am staying on the smooth side with my ride. Pick your own pleasure though.

I have a Jim Comstock/CNW head steady. No sideways movement, just up and down, like the originals were supposed to provide, but didn't. There was a noticeable change with it fitted, making it more stable and precise. I don't recall a change in vibration either way. The increased vibes only hang around for maybe a couple of thousand miles before they settle in.

milfordite · May 20, 2017

I agree that if they are really old, you should renew them as long as the engine is out of the frame. It would be a good time to change to MKIII style if the budget allows. I don't think they have to be the same front and rear. When I was riding my Commando home to Ohio from California, I goofed around and played with the clearances F/R until it was the smoothest at the speeds I was riding.(Mostly around 70-75MPH) It was fun to do and I got it really smooth. I don't know what the heck I ended up with, but the bike is nice and smooth and still handles well so I left well enough alone. One of these times when the bike is on the stand for maintenance, I need to measure them to see where they are.

brxpb · May 20, 2017

Front iso is pretty new, rear one is about 15 years old, norvil type head steady, they've always been set to 0.005" all around, but as I said, now I'm getting older (but still in the youngsters bracket on this forum :wink: ) my backside is becoming less vibe tolerant, so if I open up to say 0.010" would all have to be opened to the same measurement?

pete.v · May 20, 2017

brxpb said:
so if I open up to say 0.010" would all have to be opened to the same measurement?

Maybe or maybe not. No 2 bikes will adjust the same as with front, rear, or head steady iso's. But, although it can be quite fussy, once its right, its righteous. Trial and error!
I removed the rubber boots years ago. This makes it a bit easier. All they did was retained moisture and rusted up the shims. Unless you go mud running like hobot did, they are of no practical use (IMHO). I also think the Vernier adjusters are attractive. Why hide em?

isolastics

Similar threads