85 700 e pistons into an 83 750 es?

[Unclesol]

Have a chance to pick up a crank, rods and pistons from an 85 700 E, and was wondering about putting them into my 83 750 ES. As the 700 was screwed under the Harley tariff, would the higher compression pistons make much difference in the 750 motor?

[Nessism]

Edit: see oldschoolGS's post below.

[SqDancerLynn1]

Your going backwards & will loose 50cc

[chef1366]

Wouldn't you also need a good cylinder off the same bike?

[oldschoolGS]

The 699cc bikes were destroked only, bore is the same as the 747cc bike at 67mm.

Keep the 747cc crank and rods and use the 699cc pistons. They are slightly domed to make up for the loss of compression due to destroking. The combo will give you a tad over 10-1 as opposed to the 9.6-1 stock compression. In my experience, around 10.5-1 is the max would want to go with this TSCC head for street use on pump gas.

I have run this combo for years in my '83, it is a very easy way to get a bump in compression without boring the block or shaving the head.

Hi lift aftermarket cams work well with compression increases, if you are still running stock cams it probably is not going to be worthwile. Add cams (something in the .330 lift range) and the 699cc pistons and you will be surprised by the change.

How are those 34mm carbs working? I used them for all of the motor combo's listed above including going all the way out to 802cc. BTW, I still have that 3.5in rear as the buyer went MIA.

Good Luck, Ed.
2005 GSF1200SZ
1983 GS750ED
1992 Duc 900SS

[Unclesol]

Hey Ed!
Thanks for the info. Actually, after I put up the post, I went digging through a file I keep on ideas to use on the bike, and found you had already mentioned this combination to someone else.
I also have a chance to get the 700's cams. Would they be any better than the 750's? Otherwise, I would go shopping for the .330's as suggested.
Sorry to hear you lost your buyer on the wheel. I did find one, but it needs some cleaning up (painted by hand with a corn broom...). What are you looking to get for yours?
P.S. The carbs are still sweet! Thanks again.

[Unclesol]

Edit: see oldschoolGS's post below.

Thanks for the refresher!

[oldschoolGS]

Hey Ed!
Thanks for the info. Actually, after I put up the post, I went digging through a file I keep on ideas to use on the bike, and found you had already mentioned this combination to someone else.
I also have a chance to get the 700's cams. Would they be any better than the 750's? Otherwise, I would go shopping for the .330's as suggested.
Sorry to hear you lost your buyer on the wheel. I did find one, but it needs some cleaning up (painted by hand with a corn broom...). What are you looking to get for yours?
P.S. The carbs are still sweet! Thanks again.

Glad to hear your 750 is still running strong. I do not have the specs on the 699cc cams, I can't imagine much difference from the 747cc motor. Suzuki did also regear the smaller bike with a 45 tooth rear sprocket to make up some of the seat of the pants difference.

If you go to the trouble of doing cams, go with .325-.330 lift aftermarket cams. I had mine set at 110 degree centers and she really picked up steam at around 7500rpm. They are fairly easy on the valvetrain and will work with stock springs if they are still fresh. If you are gonna run it hard, get a manual cam chain tensioner.

Speaking of my wheel, Phucking knucklehead Qball commits to buy it and then goes MIA and will not answer my PM's. What ****es me off is the fact that I went to the trouble of removing the tire and packing it up.

I would like to get $125 for everything including the rear rotor and sprocket assembly. Everything is in very good shape. No pressure, I will put it on Ebay when I get around to clearing out some other GS stuff.

Again, good to hear from you,

Ed.