Piston Ring Clearance

Top End (cylinders pushrods etc.)
Post Reply
steve_wood
Senior Member
Posts: 953
Joined: Tue Jan 08, 2008 12:32 am
Bikes: 56 FLH, 2007 FLHRCI
Location: Belleville, Ontario, Canada
Has thanked: 49 times
Been thanked: 28 times

Piston Ring Clearance

#1

Post by steve_wood »

Man this aftermarket shite is driving me crazy. This is a complete piston kit from J&P (piston, rings, wrist pin).

Got the rings installed. End gap was fine, but the side clearance is a tight .003 whereas the spec is .004 to .005 !!

I'm really reluctant to put that piston into service with such a tight fit. Am I over-reacting or justified?

I'm commited to these pistons because the cylinders were rebored to fit them.

Any suggestions?
NightShift
Senior Member
Posts: 534
Joined: Tue Apr 21, 2009 4:20 pm
Bikes: Two Schwinns, a Hercules, and a Hiawatha
Location: Underground in Illinois
Has thanked: 3 times
Been thanked: 6 times

Re: Piston Ring Clearance

#2

Post by NightShift »

Dear Steve,

I think that fat clearance spec in the ring lands is for the fat old FL rings. If your FLH pistons have a moon with crescents inside its as good as they get.

'Spectful,
steve_wood
Senior Member
Posts: 953
Joined: Tue Jan 08, 2008 12:32 am
Bikes: 56 FLH, 2007 FLHRCI
Location: Belleville, Ontario, Canada
Has thanked: 49 times
Been thanked: 28 times

Re: Piston Ring Clearance

#3

Post by steve_wood »

Clarification:

The pistons fit in the cylinders perfectly. The machinist used the pistons to determine the correct bore.

The issue is with the fit of the rings in their grooves. You're supposed to be able to slip a .004 feeler inbetween the ring and the top or bottom of the groove. I can make a .003 feeler get in there, but that is too tight according to the spec.

Interestingly, the typical spec on the internet is as tight as .002 so maybe it isn't so bad.

But I'd feel a whole lot comfortable if more experts like Nightshift told me it was okay.
Kurt
Member
Posts: 268
Joined: Tue Jul 01, 2003 2:21 am
Bikes: 1942 U
1942 WLA
1995 Ultra
2008 Ultra
Has thanked: 4 times
Been thanked: 5 times

Re: Piston Ring Clearance

#4

Post by Kurt »

Sorry.....I misread your post....
NightShift
Senior Member
Posts: 534
Joined: Tue Apr 21, 2009 4:20 pm
Bikes: Two Schwinns, a Hercules, and a Hiawatha
Location: Underground in Illinois
Has thanked: 3 times
Been thanked: 6 times

Re: Piston Ring Clearance

#5

Post by NightShift »

Expert? Moi?
(Hahahaha.... )

Methinks the real experts whether Korean or whereever already put a little extra clearance in. They call that *idiot clearance* but dont take it personal.

Im real surprised if your endgaps werent huge, as that was a Hastings signature.

Yours didnt come in envelopes with instructions? It makes me want to scratch my beard.

'Spectful,
steve_wood
Senior Member
Posts: 953
Joined: Tue Jan 08, 2008 12:32 am
Bikes: 56 FLH, 2007 FLHRCI
Location: Belleville, Ontario, Canada
Has thanked: 49 times
Been thanked: 28 times

Re: Piston Ring Clearance

#6

Post by steve_wood »

It was a "piston kit" from taiwan ted. The rings came in a clear plastic zip bag with no instructions. How much would it have cost to include a small instruction/spec sheet.

End gaps were within spec but definitely towards the big end of the spec. From what I hear, that is good.

What do you mean by built in clearance?


Argh.
steinauge
Inactive member
Senior Member
Posts: 521
Joined: Tue Feb 03, 2009 10:05 pm
Bikes: 1938U,1949FL,1961FL,1968XL,1979FL ,1958 FL, 1965 BMW,1975 Honda CB750
Been thanked: 14 times

Re: Piston Ring Clearance

#7

Post by steinauge »

The old rule of .003-.004" of end gap per inch of bore diameter on air cooled engines is pretty reliable.we were told at service school (in 75 and 80) that ring side clearance should be .001" to .006" with .006 being wear limit.This was for the 1\16" FLH ring not the old FL ring Night Shift is talking about.I have never ever had any problem with ring side clearance in the .001-.002" range in these engines. Too much ring side clearance will cause ring flutter and breakage while not enough will cause the rings to seize in the grooves.Please note that I am not and never have been an "expert" at anything so consider the foregoing as worth what you paid for it :wink:Steve I just caught the part about the plastic bag.All the ted piston sets I have seen in the last ten years or so have had hastings rings in the hastings box.Maybe been returned and repacked??? It is a lot better to have too much end gap than not enough! Too much=blowby not enough = ring butt and seizure.Better yet is within spec-.010" to .020"
Post Reply

Return to “Top End / Cylinders / Pushrods / Lifters”