KH Piston Clearance

Production K Models

KH Piston Clearance

Postby hennesse » Wed Jan 24, 2018 3:07 pm

What is the recommended piston to cylinder clearance for stock KH ?

Any recommended sources for new pistons and valves - stock KH ???

I'm having my lower end rebuilt, and I THOUGHT I didn't have to do anything on the top end except de-carbon and lap the valves. While lapping, I found a crack between the intake valve and the cylinder bore. Kinda ruined my day! So I may need to sleeve the cylinders, and get new pistons. Might replace the valves too as the margins are getting a little thin.
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Re: KH Piston Clearance

Postby wz507 » Wed Jan 24, 2018 4:04 pm

Might also consider opening the crack slightly, brazing it closed, followed by installation of a new seat. I would not sleeve it unless absolutely necessary.

Since you said previously that you had KR heads and cams, Enfield Racing has some KR valves by Manley that might be of interest to you.

LR Cylinder crack cut-out.jpg
LR Cylinder crack cut-out.jpg (88.43 KiB) Viewed 4601 times


LR valve side of Cylinder crack cut-out.jpg
LR valve side of Cylinder crack cut-out.jpg (65.46 KiB) Viewed 4601 times
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LR brazed K cylinder.jpg
LR brazed K cylinder.jpg (75.56 KiB) Viewed 4601 times
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Re: KH Piston Clearance

Postby hennesse » Thu Jan 25, 2018 12:49 pm

wz507 wrote:Might also consider opening the crack slightly, brazing it closed, followed by installation of a new seat. I would not sleeve it unless absolutely necessary.


I'm having a professional machine shop do the work. The crack is about the same length as your photos. They've provided two options (1) install a pin to stop the crack, weld, and install new seat, and (2) sleeve it. Besides cost, what is the downside of sleeving the cylinder?

I can't find any piston fitting specs for the K or KH. For the Sportster, the service manual says .0025 to .003 loose. Should the K/KH be the same?

Interestingly, for Duo-Glide .001 to .002 loose, Servi-Car .0015 to .002, Hummer .0025 to .0035
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Re: KH Piston Clearance

Postby Mark.A » Thu Jan 25, 2018 2:26 pm

Engine fitting specifications taken from questions and answers manual of motorcycle maintenance page #179.Piston clearance .001 to .0015 at skirt bottom 90 degree to pin.
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Re: KH Piston Clearance

Postby hennesse » Thu Jan 25, 2018 3:12 pm

Mark.A wrote:questions and answers manual of motorcycle maintenance page #179.


I'm not familiar with that book. From OCLC I see that it's a Bagnall Pubs annual book (kinda like a Chilton's manual). What year is it from, and are those specs specific to the K/KH ?
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Re: KH Piston Clearance

Postby Mark.A » Thu Jan 25, 2018 3:58 pm

Sorry forgot to list as K model specifications. The book is the 21st edition copyright 1970 they list all engine fittings for the K . Not sure how to post pictures .Would like to post the whole page
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Re: KH Piston Clearance

Postby thefrenchowl » Thu Jan 25, 2018 6:40 pm

My Bonneville Salt Flats KHK (supercharged on pure methanol) pistons are fitted with 1.5 thou clearance. I've always used that figure in the 30 years I've owned it... Same on all the iron head Sportsters I've owned over the years.

Only exception was Sportsters strokers S&S 3700 or 3500 forged pistons series, 3 thou...

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Re: KH Piston Clearance

Postby Geodoc » Thu Jan 25, 2018 9:13 pm

Just bought a set of pistons w/ rings, wrist pins & clips + Manley valves for a KHK from:

http://enfieldracing.com/

His pistons are Wisco that he had made to suit. I haven't got them in my hand yet, but Wiseco usually comes with installation instructions for clearance & ring end gaps. Being forged rather then cast, I'd imagine that the piston clearance would be larger than with the stock ones.

hennesse wrote:What is the recommended piston to cylinder clearance for stock KH ?

Any recommended sources for new pistons and valves - stock KH ???

I'm having my lower end rebuilt, and I THOUGHT I didn't have to do anything on the top end except de-carbon and lap the valves. While lapping, I found a crack between the intake valve and the cylinder bore. Kinda ruined my day! So I may need to sleeve the cylinders, and get new pistons. Might replace the valves too as the margins are getting a little thin.
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Re: KH Piston Clearance

Postby EKHKHK56 » Fri Jan 26, 2018 12:21 pm

Stock for street is 1 to 1.5 clearance. Cast type. Forged definitely grow more. Might give Wiseco a ring see what their spec is for this application. Yes they will stick at 1.5 clearance...They probably have different clearances for different applications. Being street stock you want less clearance than if you're running fuel and drag racing. The two ends of the scale.
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Re: KH Piston Clearance

Postby starcain » Fri Jan 26, 2018 12:46 pm

Here is a piston installation instruction insert that came with a NOS original set of Harley K model pistons I have. They are calling for .001" to .002" clearance. Pretty consistent with what everyone is saying.
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