anyone ever offset engine ?

The matching rear wheel and tire combo is too wide, the tire is a 160 It would hit the chain if centered and I need to widen the swingarm anyway because it whould hit both sides... SO I got to looking... It looks as though I could cut almost cut 3/4 off the left side Iso spacers and slide the package to the left and space the right...

Any thoughts?

Why on earth would anyone want a 160 rear tyre?

Bob.

I think I follow you. Sliding the engine and tranny to the left still doesn't change chain to tire clearance unless you shim the rear brake/sprocket (assuming it's not a MKIII) from the hub a corresponding amount. As I see it, you have to move the rear sprocket the same amount as the tranny. This might be a bit tricky. I know of one of our online parts distributors who said he was developing a wider swing arm to accommodate a wide tire. When I mentioned that he needed to move the rear chain he seemed perplexed. I run a 120-18 rear and I have about a 1/4" clearance on both sides. Left side being the chain guard, right side the swing arm. BTW, I don't think you have much room to play with the front iso. Whatever you move you have to do the same, front and rear.

Moving the engine may improve the bike or ruin it.

As stated in other threads here, a lot of engineering goes into the precise placement of an engine in the frame of a bike. A half inch in any axis can result in a great handling bike or a nightmare, especially an engine like the Norton, which has certain harmonic frequencies at different engine speeds.

As an example, I can think of the BSA Rocket 3/Triumph Trident. The BSA used a different crankcase than the Trident, rotating the cylinders somewhere around 10-15 degrees forward. This didn't alter the center of gravity much, but vastly improved the handling characteristics over simply dropping the Trident engine in the BSA frame. Unfortunately, the slightly better-handling BSA did not have as comfortable riding position as the Triumph, and BSA stopped selling motorcycles under their brand right around the time they came out with a 5 speed gearbox for the A75/T150

I noticed a chopper at a local bike night a few weeks ago that had one of those monster rear tires on it - a 360. Instead of offsetting the engine, the final drive had an offset sprocket mounted on the swingarm pivot. Chain went from the transmission to the intermediate drive sprocket, final drive belt went from intermediate driven sprocket to the rear wheel. This way, builder kept his standard engine layout, but could put any width tire on the rear he wanted. I've also seen intermediate sprockets on bikes with hyperextended swingarms - 2 100-link chains rather than one 190-link chain.

I have a set of spacers for a sprocket for a Mark III rear wheel, they were on a chopper that had a 5.10 rear tire. The spacers left about 1/4" of contact between the sprocket tabs and the cush hub sockets; not a lot.

The horsepower drained from spinning the added weight of a 160 rear tire has to be significant, and the changes it's going to make to the commando frame probably aren't going to be a great trade-off.

Or, it might all work wonderfully, just as bill said...

I seem to remember that the production racing Commandos that Peter Williams and the Norton works team raced had the engine spaced slightly to the right and a bit higher up to obtain better ground clearance for cornering. The primary drive case was seemingly the lowest point by quite a large margin. They also ran both exhausts on the right side. So moving the engine and gearbox to the left would probably exacerbate this clearance problem. I also recall reading reports on this forum and others that putting too wide a rear tyre on a Commando compromises the handling.

How much work do you want to do?

Hi
My Sprint bike! haha has the gearbox cases altered to move the gearbox across. As per Grandpaul & nearly all triple race bikes, an offset gearbox sprocket.All this machined so that the belt drive re-alines the crank pulley & clutch. It also has a spacer made for the chaincases to allow all this to run inside them.
Terrific engineering or lots of money.
If you are building a chopper & you just want the looks? maybe. Personally I would just run a smaller rim size 16"
From my point of view, I got a modern YZF Yamaha front end, with good fork action & handling that is no better than my Seeley MK3 on original size tyres!

As to ofsetting the engine. I purchased a T140 chopper in a special frame that was featured in a few magazines. I wanted a non race/ clip on bike to take the wife out on. It was offset to the the left by nearly an inch & had a big tyre that looked square to me. On right handers it was as sound as a pound on left handers a thruppeny bit. (Coins of the realm) I would constantly correct it at all points around the corner. Never took her out on it, cos it scared me & even I did not ride it in the wet!
Good luck in whatever direction you take.
all the best Chris

dave M said:

I seem to remember that the production racing Commandos that Peter Williams and the Norton works team raced had the engine spaced slightly to the right and a bit higher up to obtain better ground clearance for cornering. The primary drive case was seemingly the lowest point by quite a large margin. They also ran both exhausts on the right side. So moving the engine and gearbox to the left would probably exacerbate this clearance problem. I also recall reading reports on this forum and others that putting too wide a rear tyre on a Commando compromises the handling.

Click to expand...

Dave....Shush !... :shock: - The Triumph boys still don't know how the works 'production' racers were modded. If they hear now they'll probably appeal ! (not of course that they weren't doing it too)

You're quite correct in what you say by the way. I've looked at one that Norman White was building with the same mods.

Just remembering about the goofball setup on Commandos where the right tire is offset to the right on 99% of all of them, maybe 1/4' or so? Well, there you go, you ALREADY have an offset to start with!

I didn't explain my thoughts very well...

I don't nessessarily want to offset the engine... I am considering it because of the available parts I have and the fact that the parts were free.

It was given matching frontend and wheels from a Suzuki sport bike. The front and rear wheels are 17inchers, the rear wheel is 4.5 wide and the tire is a 160... the tire will not fit in the swingarm (so I'd need to build one, widen the existing one or find one that could be adapted) If the tire did fit the swingarm, it would hit the chain unless I ran the tire offset. That is why I brought up moving the engine to the left... to see if anyone has done it?

I know getting both tires running in the same plane is key to handling, the engine.tranny package would have to be moved to do this... but then it would be unbalanced, heavy on the left side... and as stated above, closer to hitting in a lft turn.

I also know as descibed above, a wide tire with the tire offset (not aligned with the front) made for great right turns, but suffered left turns...

I personally do not care for the fat tire craze! I work in a motorcycle shop and hate test riding them! either way the accomplish it, offset drive or offset tire... anything over a 200 tire steers like crap because the tire to road contact patch is out of alignment the farther you lean...

why not just move the gearbox to the left, fit a dommie mainshaft and run a delt drive! I had to do it on one of my race bikes a long time ago! Mick Hemmings sells dural commando clutch centres modified to fit a dommie mainshaft!!