Topic: Are 77 and 78 750 frames wider for chain clearance ?

[754]

 I put a 78 motor in a 74 frame.  Got everything sorted out I think.  With stock swingarm.
 But I doubt there is enough room in there to run an offset sprocket up front.
 Makes me wonder if they widened the frames in those years, for a bit more  clearance.
 Anyone here running offset front in a late frame, how much clearance do you have?

[Jerry Rxman Griffin aka MuthaF'er]

Frank, the 77/78 engines already have a 10mm offset up front to accomodate the wider output shaft bearing. The 77/78 swingarm also had a 10mm offset with a 10mm offset rear sprocket carrier. I changed both of these when I put the 78 engine in my 75 frame.

"Stock swingarm"?? 74 or 78?

[754]

 I have the motor in my Frame,  moved rear wheel over too , but not seeing much over 10 mm clearance.

[Jerry Rxman Griffin aka MuthaF'er]

Forget the chain guard and hope the chain doesn't rub the shock. $$$$$.25 

When are you hoping to show up now?

[754]

My chainguard bolt hits frame I will move it back, and my chain clears shock.
 Leave Sunday should be there Mon nite.
 Where will you be?
Will have to contact you via email or pm..

[Jerry Rxman Griffin aka MuthaF'er]

I'll roll in tomorrow 5pm +/-. Just gotta ice down the beer in the morning and hit the road.

I will not be set up online at The Salt. Call gets immediate answer. Text whenever. Email/PM in the evenings if I'm not toasted  #$%* DOES happen      719-963-3080

Base motel is Motel 6. Look for the red Vette.

[scottly]

I have the motor in my Frame,  moved rear wheel over too , but not seeing much over 10 mm clearance.

You're only supposed to move the rear sprocket over, not the wheel. The bike might feel a bit funny in turns with the rear tire 10mm out of line with the front.

[754]

 Sporty I meant sprocket, i added  1/4   spacer on chain side, that may have moved things out of line.
 Sure I am within 1/8 inch.

[madmtnmotors]

>The front sprocket covers are different, so hopefully you got the front sprocket cover with the K8 engine? Using an older front sprocket cover on a newer engine will often cause the chain to "self clearance" the front sprocket cover. The most notable differences are at the top rear at both the opening for the chain itself as well as the depth of the upper mounting screw boss. You'll notice the screw boss on the lower mounting screw is cut away on the newer cover as well. The early cover has what appears to be an extra "guide" post cast on the inside of the cover too. I have never seen this extra "guide post" on a later model, but there may be early models that might not have it, so don't use that as the only identifier... be sure to measure too! The earlier model sprocket cover is on the left:











>The rear swingarm is wider on the 78'

>The upper shock mount has an extra 3/8" shoulder to move the shock body out to match the wider swingarm:





 

[754]

Handy tip the early sprocket cover fits, i could not get the  black late one in.
 Good thing as I did not loctite my front sprocket bolt and it fell out.
 Chain was grinding on the cover , but sprocket was still 3/4 of the way on the shaft.
Probably kept sprocket from coming off.

 Yes I know about the wider longer late swingarms, and the shock mount being further out. .
 My question still is , with an offset sprocket mounted on late engine, is there any room left, between chain and frame, in the area  above the swingarm pivot ? Can't be much wiggle room there.

[madmtnmotors]

Handy tip the early sprocket cover fits, I could not get the  black late one in.

There is a trick to getting the later model sprocket cover into place, it requires a little twist of the wrist. I probably need to do a video since more than one member here has struggled with them.

My question still is , with an offset sprocket mounted on late engine, is there any room left, between chain and frame, in the area  above the swingarm pivot ? Can't be much wiggle room there.

Not sure I understand. The later engine already has the 10mm (3/8") longer output shaft so why would you use an offset sprocket on the front with a later engine? This would make your front offset 20mm (3/4") instead of 10mm? For what purpose? The offset front sprockets are used to align an older engine with a newer swingarm and wheel with the taller rear sprocket carrier.

[Motorcycle jones]

The 78 has a wider sprocket hub.  That is why you are having this problem.

The 78 also has a longer swing arm.

[madmtnmotors]

The 78 has a wider sprocket hub.  That is why you are having this problem.

The 78 also has a longer swing arm.

He is trying to align a later engine with an earlier swingarm. He has added a spacer behind the rear sprocket, but for some reason he seems to think that the front sprocket has to be offset too, except that the offset is already "built in" to the later engine. The extra 10mm outboard offset in the front sprocket of the later engine is why the rear sprocket has to be moved over, either with an offset sprocket in the rear, or a spacer behind the rear sprocket, or by using a later rear sprocket carrier and cutting 10mm off the chain side wheel/axle spacer. Using the later engine with the older frame and swingarm only requires that the rear sprocket be offset, not the front. A standard sprocket should be used on the front with the offset sprocket on the rear only when transplanting a newer engine into an older frame with the older swingarm.

[754]

Forget what I am doing, it works.
 On a day a guy wants to run a wwwiiiiiddddeee tire, if you put an offset front sprocket on a long shaft motors is there room ? That was the question in the first place. It's likely not a problem on custom frames.

[Patrick]

That '78 also came with 630 chain stock.

[madmtnmotors]

Forget what I am doing, it works.
 On a day a guy wants to run a wwwiiiiiddddeee tire, if you put an offset front sprocket on a long shaft motors is there room ? That was the question in the first place. It's likely not a problem on custom frames.

Ahhhhh….. now I understand. Not sure there is any "extra" room on the later frames, I think they just used up what room they already had. "dragracer" Frank Loney might have more insight, he's been racing his quite a while. I could measure the chain to frame clearance this weekend on my K8 to see how much room is left on the later frame.

That '78 also came with 630 chain stock.

630 chains and 530 chains are the same width (30). Only the roller diameter and distance between the pins is different (6/8 vs 5/8):

https://www.3guyz.com/vtwinfaqs/76-530630chain

[scottly]

Beat you to it, Wibur. Frank, the late frame is the same width in the areas above and below the swing arm pivot where the chain passes. Also, the swing arm pivot is the same width.

[madmtnmotors]

The late frame is the same width in the areas above and below the swing arm pivot where the chain passes. Also, the swing arm pivot is the same width.

I thought they were. 

[madmtnmotors]

In stock trim the K8 only has about 1/4" between the chain and the forward down tube of the frame (the first down tube just behind the front sprocket). Sorry, no picts since some disassembly would be required to get a decent photo.