New project Introduction and questions

marshg246 · Jul 30, 2025

rv1890 said:
Next step. Piston ring gap. I'm using Hepolite pistons with their rings. PVD faced top compression ring, cast iron second compression ring, and two piece oil ring.

Can someone confirm my math? My bores are .060 over.

2.874 (standard) + .060 over = 2.934

If the rule of thumb is .004-.006 gap for every inch of bore then:

2.934*.004 = .0117
2.934*.006 = .0176

So I should be setting the gaps between .012-.018 on the first and second rings, correct?

The ring gaps are in the workshop manual - no need for math. Generally, I have not needed to adjust them at all with Hepolite complete sets. I only would if the gap was too small, but it never has been.

BTW, yes, the oil rings are hard to get in the cylinder. DO NOT "adjust" the spring - they come correct!

rv1890 · Jul 30, 2025

Sounds good. I was thrown off since the workshop manual states it for standard bore and mine is .060 oversize...Unless I missed that part of the manual.

Guess I'll throw them in how they are out of the box and confirm at minimum a .012 gap??

htown16 · Jul 30, 2025

Slightly too big is better than slightly too small.

marshg246 · Jul 30, 2025

rv1890 said:
Sounds good. I was thrown off since the workshop manual states it for standard bore and mine is .060 oversize...Unless I missed that part of the manual.

Guess I'll throw them in how they are out of the box and confirm at minimum a .012 gap??

AFAIK, the "rule" is for standard bores. Once you go over, you still be the same gap so no math needed by the user, only the manufacturer.

rv1890 · Jul 30, 2025

oh, ok. That makes sense. I haven't checked yet as to what they are out of the box. I'll do that first and go from there

rv1890 · Tuesday at 6:48 PM

While I wait for some parts to arrive I plan to tackle the carbs next. Bike is a 750 and it has Amal 932 carbs.

I had the housings vapor blasted and they cleaned up nicely, but the jets and needle have seen better days.

I purchased the bike not running, so I dont know what was working or not. My research is showing that the 932's were for the 850 commandos, but can be used for the 750. It currently has a .106 needle and 220 mains. If I get a rebuild kit is it ok to go with .106 and 220 again?

htown16 · Tuesday at 7:09 PM

L.A.B. · 2025-08-06T00:36:36-0600

rv1890 said:
My research is showing that the 932's were for the 850 commandos, but can be used for the 750.

932s were fitted to the Combat 750 models in 1972 and most later 750s.

Shelby-Right · 2025-08-06T02:57:00-0600

It's not a bad idea to make the second ring gaps slightly bigger as it stops a build up of pressure between the rings and stops ring flutter .

N0rt0nelectr@ · 2025-08-06T12:46:05-0600

rv1890 said:
Thanks Dennis, yes I plan on measuring the crank to verify con rod bearing size. I also will separate the crank for cleaning since there was lots of sludge.

Also, I didn’t notice the “restoration” section of the forum. Do I need to move it myself or does an admin need to?

There is a set of crankshaft nuts, bolts and studs along with the metal strips that retain the nuts and the locating dowel. Sounds complicated but it isn't.
John in Texas

New project Introduction and questions

marshg246

rv1890

htown16

marshg246

rv1890

rv1890

htown16

L.A.B.

Moderator

Shelby-Right

N0rt0nelectr@

Similar threads