piston ring side clearance

Status
Not open for further replies.
S

seattle##gs

Joined
Oct 28, 2014
Messages
1,996
Country flag
I have a 750 with JCC pistons and a mysterious over oiling problem. The rings are fairly new and the pistons don't show much wear. The side clearance on the two top rings is .004 and the 3-piece oil ring is .005. I think the clearance should be less than .002?
The head will be inspected Monday and two inlet guide seals installed. The left ex port had plenty of wet oil in it though new guides and valves had been installed about 3 months ago. Fresh rings at that time. I have been chasing this problem for 2 years. 3 months ago I pulled the original head off and discovered a loose ex guide on the left side so I thought I had found the problem. Only partly however. The fresh head (different head) with all new stuff. New rings. The problem persists so I'm looking in new areas which brings me to ring side clearance.
 
seattle##gs said:
I have a 750 with JCC pistons and a mysterious over oiling problem. The rings are fairly new and the pistons don't show much wear. The side clearance on the two top rings is .004 and the 3-piece oil ring is .005. I think the clearance should be less than .002?
The head will be inspected Monday and two inlet guide seals installed. The left ex port had plenty of wet oil in it though new guides and valves had been installed about 3 months ago. Fresh rings at that time. I have been chasing this problem for 2 years. 3 months ago I pulled the original head off and discovered a loose ex guide on the left side so I thought I had found the problem. Only partly however. The fresh head (different head) with all new stuff. New rings. The problem persists so I'm looking in new areas which brings me to ring side clearance.
Click to expand...
From memory I can't remember the maximum clearance. If your side clearance exceeds the limit you can/could get wider rings and have the ring grooves remachined to suit. Or get a new pair of pistons. Preignition can accelerate ring groove wear .
Dave
 
Far too much clearance . I had similar on my Atlas with old pistons . After carefull measuring most of the wear was on the rings( not what I expected!) A new set of rings has solved the issue, but in your case you have a missmatch of wrong parts. You need to buy rings from a source that Knows and reconditions engines . 2 Thou would be max for me.
 
norton bob said:
Far too much clearance . I had similar on my Atlas with old pistons . After carefull measuring most of the wear was on the rings( not what I expected!) A new set of rings has solved the issue, but in your case you have a missmatch of wrong parts. You need to buy rings from a source that Knows and reconditions engines . 2 Thou would be max for me.
Click to expand...
0.003 thousands between skirt and bore, measure with a feeler gauge.
0.005 tho is considered a racing clearance.
 
The side clearance on the two top rings is .004 and the 3-piece oil ring is .005. I think the clearance should be less than .002?

Was the question, nothing to do with bore clearance but the clearance of the ring in the piston ring slot.
 
Slightly off topic:

I don't know if you can answer this, or even will answer it, but here goes.

Since you live in West Seattle according to your profile. Who does machine work and is old enough to understand Norton engines in the Seattle area?
 
Ring land clearance is a problem with the old JCC/Hepolite design. The heavy thick rings slamming up and down with each stroke tends to loosen them up. Its not unusual to be able to fit a .006" feeler gauge in between the rings and the ring land of a used piston and by that time its starting to smoke.

Thats one of the reasons modern pistons have gone to thinner rings and tighter clearances (usually less than .002" ring land clearance). The ring lands stay tighter. The lighter rings also eliminate the so called "ring flutter" problem.

Also consider switching to spring loaded viton guide seals.
piston ring side clearance
 
I have been going to AUTOSPORT in Ballard for a long time. The owner/machinist has several britbikes himself and cares about his work.
So does anyone make Norton pistons with thin rings? Ones that work with standard rod length?
It now sounds like ring lands are the weak point in Norton pistons and the area that should be checked first. Instead of re-ringing install a whole new piston....or keep replacing sparkplugs often.

NEW QUESTION...I just pulled the head off an old 750 motor and it had hepolite pistons with a dome. The look almost new and a .002 feeler gauge was hard to fit between ring and groove. How much does this dome add to the compression? The head is RH6
 
seattle##gs said:
I have been going to AUTOSPORT in Ballard for a long time. The owner/machinist has several britbikes himself and cares about his work.
Click to expand...
Thanks

I'll look into Autosport if/when I need some machine work done. Not knowing where to go has kept me from tearing down a motor that doesn't really need to be torn down. Now I have no excuse not to fix something that isn't broken.
 
Schwany said:
Thanks

I'll look into Autosport if/when I need some machine work done. Not knowing where to go has kept me from tearing down a motor that doesn't really need to be torn down. Now I have no excuse not to fix something that isn't broken.
Click to expand...

seattle##gs said:
I have been going to AUTOSPORT in Ballard for a long time. The owner/machinist has several britbikes himself and cares about his work.
So does anyone make Norton pistons with thin rings? Ones that work with standard rod length?
It now sounds like ring lands are the weak point in Norton pistons and the area that should be checked first. Instead of re-ringing install a whole new piston....or keep replacing sparkplugs often.

NEW QUESTION...I just pulled the head off an old 750 motor and it had hepolite pistons with a dome. The look almost new and a .002 feeler gauge was hard to fit between ring and groove. How much does this dome add to the compression? The head is RH6
Click to expand...
Contact "Lcrken" about pistons that fit stock rods and have thin rings.
If you have domed hepolite pistons then they are "powermax" and very rare as in they dried up in the early 1980s I think they are 10:1 CR but I'm not sure. I raced with a set but I revved it so high that I loosened up the ring lands and the rings broke. They should be OK on a street bike and last as long as any old hepolites.
 
Status
Not open for further replies.

Similar threads

D
  • Locked
piston ring side-clearance
Replies
3
Views
988
kerinorton
K
NORTSTER1974
  • Locked
Excessive blow by through breather hose
Replies
9
Views
1,215
NORTSTER1974
NORTSTER1974
Back
Top