Jockey Journal Forum banner
1 - 20 of 27 Posts

·
Premium Member
Joined
·
6,351 Posts
Discussion Starter · #1 ·
Alright, I've got an 80" shovel motor and the cylinders will be on their last overbore (.040); so next time I will need new jugs to start over with.

Let's put aside the loss of cubic inches; what I want to know is are 74" and 80" jugs interchangable? Certain years, maybe?

I want to stay with factory here, and if 74" jugs would fit it would certainly open up my options for finding decent used set.

Drop science.
 

·
Registered
Joined
·
1,576 Posts
Yup, according to the "What Fits What" book, they will interchange. The 80" uses longer studs because of a thicker base. And if you could find a standard bore set, you would have a lot of meat for longevity.
 

·
Premium Member
Joined
·
6,351 Posts
Discussion Starter · #3 ·
Okay, I knew about the studs but if the 74 has a thinner base, then it's not an issue. Cool.

I was thinking about oil returns too...I don't have a 74 set to compare directly to.

Good news, thanks.
 

·
Registered
Joined
·
115 Posts
Paul, The stroke on the flywheels are different from 74 to 80. Yes the cylinders will interchange but you will need to change the flywheels also or go to custom pistons with a revised pin height. If you are looking for used factory 80 inch cylinders the best way to tell is the base pad is approx 1/2 inch thick squared off not tapered like the 74 cylinders. Tim
 

·
Registered
Joined
·
1,583 Posts
Seems like I recall, you can safely overbore 74" jugs to an ungodly amount and use stock 80" standard bore pistons, without changing flywheels or screwing with $pendy custom pistons. Maybe somebody else can chime in.
 

·
Registered
Joined
·
115 Posts
I may catch a bunch a flack for this but for a stock rebuild the v-twin piston and cylinder kits work very well.
I did a little research the stock 74 inch stroke is 3.968" and the stroke of an 80" is 4.250. The rods are the same length hence the different pin placement on the 80 inch pistons.
Tim
 

·
Registered
Joined
·
1,583 Posts
Since it looks like the good Dr. s question has been answered, allow me to veer a little. Is there Any piston to run with a short stroke( 3-31/32") and 3-5/8ths Big bore, for a hi revvin mill for a light bike?
 

·
Registered
Joined
·
2,315 Posts
There aren't any pistons straight off-the-shelf for 3 5/8" bore and 3 31/32" stroke that will equate to a decent enough compression ratio to make the cost of boring the cases and the parts themselves worth it. You can have pistons made to whatever CR you want, but you're talking a lot more work than just bolting something together (CCing combustion chambers, claying the motor for valve to piston clearance when utilizing a proper cam, etc.). It would be nice to have something off-the-shelf, as you'd be a good bit closer to square with a 3 5/8"x3 31/32" motor, but the gains wouldn't really justify the expense.

Another thing to consider is the valvetrain, which having it setup to where it doesn't float and you have a mechanical overrev is key as well.

I've thought very seriously about doing a set of 3 1/2" wheels (61ci E/EL) with 3 5/8" jugs and making a REALLY high revving oversquare motor, but the amount of money to make it actually useful would only be justifiable if you had cash to burn.
 

·
Registered
Joined
·
1,576 Posts
Forget it, you're not getting a stroker shovel no matter how good bustedlifter makes it sound.
Hahaha! When I was thinking of going to a stroker the guys at the shop I deal with said there's a big downside to them. I asked what it was and they replied that stock will never be good enough again. They were correct.
 
1 - 20 of 27 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top