Maybe this has been covered but I did a search with no results. I'm trying to restore a 1966 all original bike. The cylinders are already at 40 over and need replaced. I see you can go 50 over but seems like the walls would be pretty thin. I've been looking all over the web for USA made stock replacements. Looks like S&S used to sell a set but no longer available for 74" all I see is 80". I want to keep this bike as true to original as possible. Hate to put ~ parts in it. Trying to limit it. Anybody have any advice?
You should be able to take it out to 70 thou. 50 thou should be a no-brainer. A very common practice for the 74" motor is to knock 'em out to .060 over and stroke to 4-1/2", for an 82 incher.
There are 74" aftermarket cylinders out there that were made by a company called Dixie. When they went tits up, they sold warehouses of their stock by the pallet, and now you find it all over the interweb, espeically on ebay. Just for the giggles of it, I bought a pair of the 74" cylinders. They are not from Taiwan, but from Japan. Far as I can tell, they look fine and I would not hesitate to use them should the need arise. Search on "BMI Karts".
-JW
Agree, my Shovel/Pan was 0.070" over with OEM 74" cylinders. Never a problem with the motor.
I've run a couple hard at .060 with the 4 1/2" stroke. That's higher piston speed running low gear ratio on top of that. I always came up with another set of barrels and never did go .070. I would have without a second thought though.
JW, IIRC the 4 1/2" stoke was 84" and by .060 it was close to 86". I'd have to do the math though.
86.4" :SM:
Thanks for all the replies. This is my first Shovel project so I'm just making sure of things before I screw it all up. I'm sure I will be posting some more questions. Thanks again.
Yes, please do, there is a lot of knowledge and experience in this group. And just so you know, we like pictures. A lot.
:SM:
And big WHOOPS about the 82", that was a typo.
:kick:
-JW
Quote from: JW113 on January 24, 2020, 06:54:16 PM
You should be able to take it out to 70 thou. 50 thou should be a no-brainer. A very common practice for the 74" motor is to knock 'em out to .060 over and stroke to 4-1/2", for an 82 incher.
There are 74" aftermarket cylinders out there that were made by a company called Dixie. When they went tits up, they sold warehouses of their stock by the pallet, and now you find it all over the interweb, espeically on ebay. Just for the giggles of it, I bought a pair of the 74" cylinders. They are not from Taiwan, but from Japan. Far as I can tell, they look fine and I would not hesitate to use them should the need arise. Search on "BMI Karts".
-JW
Yes BMI Karts and Parts Versailles, Ohio. They bought out the Dixie Distributing remaining inventory.
No issues whatsoever boring a 74" to .050"-.080" over....at .080" it is a plus .020", 80" bore dimension.
Plenty of pistons available.
Just finished a nice 1966 engine for another shop.
Interesting, did not know you could use the +30 80" pistons in a 74". Don't they have different piston pin heights?
thanks,
JW
Shovelhead (1978-84) 80" compression height 1.270"
Shovelhead (1966-79) 74" compression height 1.436"
Yes you could use the +30 80" pistons in a 74" but the compression ratio would be very, very low
Quote from: JW113 on January 28, 2020, 08:50:52 AM
Interesting, did not know you could use the +30 80" pistons in a 74". Don't they have different piston pin heights?
thanks,
JW
And you cannot, and you know that..... :banghead:
The BORE dimension only, is what I was referencing.
Wrist pin bore C/L difference is .156"........... :sheep:
Thank you very much....
OK thanks for clearing that up. I've never seen .080 over pistons for a 74", but then I have never looked either. Hence my question.
-JW
Ok so I bought 50 over pistons from BMI. I ordered J11228-50 cast pistons but I think I received 11228-50 forged pistons. They have TRW 11228 stamped on them and are shiny not dull aluminum. Anyone know the recommended cylinder clearance for these? The paper work that cam with it says .001. Seems kind of tight to me. I though forged piston clearance had to be a little larger than cast due the heat rate difference.
Just me, but I'd never run less than .002 clearance with iron cylinders. Maybe a bit more. Those long skirted Shovelhead pistons aren't going to rock in the hole like these modern slipper skirt pistons do. But I leave this decision to guy that's going to do the bore & hone work.
-JW