KH Piston Clearance

Production K Models

Re: KH Piston Clearance

Postby EKHKHK56 » Sun Feb 04, 2018 8:27 pm

Geo, TJ mentioned you are going through whole engine. Good idea. You just don't know who did what when plus wear and tear with out going the whole nine yards. These take a lot of time to set up correctly. Mainly in bushing work. Bushings are great. You probably know all this from Sportster work. After years of running, time to make races round again. Measure x y axis, etc. Top bottom....crank race bushings wear egg shaped in Harleys because of power pulses. They must be lapped round than to next oversize rollers. New bushings are not exempt. Press a new transmission output bushing into a case and it will distort to tighter than 0. Often these become round at 0 oversize when lapped with new shafts and all. Go slow, measure often. No plugs or oil modifications are necessary in crank. Lower end rod side clearance must be DOUBLED FOR COMPETITION or oil will stack, burn and destruction will follow. KRTT KHRTT any serious K road racer or dirt screamer....and what else....Erik K :geek:
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Re: KH Piston Clearance

Postby Geodoc » Sun Feb 04, 2018 8:49 pm

No. Only a top overhaul including replacement of the stroker plated "K" barrels that were on it with the KHK ones you sent him & new pistons & valves. Other than that, installed plug inserts to go back to 14mm from 18mm, through cleaning of carb, petcock & tank, new points. That's it.

EKHKHK56 wrote:Geo, TJ mentioned you are going through whole engine. Good idea. You just don't know who did what when plus wear and tear with out going the whole nine yards. These take a lot of time to set up correctly. Mainly in bushing work. Bushings are great. You probably know all this from Sportster work. After years of running, time to make races round again. Measure x y axis, etc. Top bottom....crank race bushings wear egg shaped in Harleys because of power pulses. They must be lapped round than to next oversize rollers. New bushings are not exempt. Press a new transmission output bushing into a case and it will distort to tighter than 0. Often these become round at 0 oversize when lapped with new shafts and all. Go slow, measure often. No plugs or oil modifications are necessary in crank. Lower end rod side clearance must be DOUBLED FOR COMPETITION or oil will stack, burn and destruction will follow. KRTT KHRTT any serious K road racer or dirt screamer....and what else....Erik K :geek:
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Re: KH Piston Clearance

Postby Geodoc » Sat Feb 10, 2018 4:38 pm

GuS wrote:Erik.

wz507.
The Enfield pistons are beauties..
I would really appreciate if you took your time to measure the piston hot/cold. Front to rear top and bottom of skirt. Sideways also, but since the sides are shaved off, that would only make sense to measure on just below the oil ring.

GuS


Measured the Enfield / WISCO pistons after getting up to temp in boiling water. Difference in diameter from room temp across 90 deg. from pin axis is about .0035". Used a .004" clearance for the cylinder bore for the machine shop.
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Re: KH Piston Clearance

Postby EKHKHK56 » Sat Feb 10, 2018 5:02 pm

Good info, thank you George. She will be happy at 4, be an easy break in with no worries.
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Re: KH Piston Clearance

Postby Geodoc » Sun Feb 11, 2018 6:25 pm

It was discovered that the guides from Enfield as "KR" spec, meaning that the stems measure ~.310" - about .027" smaller then the stock KHK valve. Uh-O. These are apparently the only valves he sells for the K Series. Going to take the cylinders w/ guides installed to a local engine shop for the guides to be K-Lined up to an appropriate size.

What kind of stem to guide clearance are you guys running?



G
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Re: KH Piston Clearance

Postby EKHKHK56 » Mon Feb 12, 2018 4:52 am

.003" to .005" with a large .008" as max wear. Dip the stems in STP before assembly.
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Re: KH Piston Clearance

Postby EKHKHK56 » Mon Feb 12, 2018 5:02 am

That's large stem which is std. Small stem KR is tighter .0025"-.003" w easy break in.
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Re: KH Piston Clearance

Postby xlh59 » Thu Feb 15, 2018 5:55 am

Hi All,

I hope its "OK" if I switch back to some aspects of the original quesion:

I am also considering to resleeve on of my cylinders as it would need a 0.06 oversize piston while the other cylinder is fone with 0.02 -- so let me repeat Hennesse´s question: whats the downside of resleeving the calinder?

I also have found a hairline crack between one intake and the cylinder bore -- basically exactly like the described one. I went to my engine expert (who is specialized on flathead engines) and he told me "dont touch it" ? The brazing solutions seems fine to me (from an metallurgical point of view) but then I would need to install a new seat?

Talkin about valve seats I would switch to the KH valve discusion ...

Thanks and greets
Ralf

BTW: This forum is an incredible source of information for me!

hennesse wrote:
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 wz507 » Thu Feb 15, 2018 1:01 pm

xlh59 wrote:Hi All,
I am also considering to resleeve on of my cylinders as it would need a 0.06 oversize piston while the other cylinder is fone with 0.02 -- so let me repeat Hennesse´s question: whats the downside of resleeving the calinder?

Nothing. See below.

xlh59 wrote:I also have found a hairline crack between one intake and the cylinder bore -- basically exactly like the described one. I went to my engine expert (who is specialized on flathead engines) and he told me "dont touch it" ? The brazing solutions seems fine to me (from an metallurgical point of view) but then I would need to install a new seat?


Both sleeving and braze welding have been used successfully for more than half a century to address the situation you describe. I don’t know what your specific project looks like (the nature of the crack and the larger overbore cylinder), but as your mechanic noted, the crack described may not even be an issue. K Models are strange in this regard as many heads and cylinders exhibit apparent “cracks”, yet these cracks never grow and tend be more superficial than structural deficiencies.

My suggestion regarding avoiding sleeving is simply one man’s opinion (mine) on the matter and does not take into account the myriad extenuating circumstances that may be relevant to the specific situation such as you describe (mismatched bores) and as mentioned above.

If a “real” leaky crack exists in the cylinder I like braze welding as a first remedy because it is a robust solution that leaves the cylinder fully intact and requires only the installation of a seat to resolve the issue. If I need a sleeve at some point in the future when the bore is too large it can always be installed then.

Sleeving is likewise a robust solution and has a few other minor attendant considerations. The structural integrity of the cylinder is strongest as-cast and machined, and every bore job thereafter weakens it slightly (the reason we don’t like to go much over 0.060” OS, with sleeve installation being the largest over-bore it will ever see). Because the sleeve does not make intimate contact with the cylinder (both cylinder bore and sleeve are machined surfaces and therefore an extra interface [sleeve to cylinder] is interposed between the heat source [the bore] and the cooling source [the fins]), the efficiency of heat transfer will be higher with the virgin cylinder than with a sleeved cylinder.

As mentioned at the outset both braze welding and sleeving are satisfactory solutions for your issue and will work fine. My rationale for favoring the braze weld over sleeving is given above. I’m not at all averse to sleeving, just not my first choice as I’d save sleeving for somewhere down the road when the bore is used up. My $0.02. And remember, you get what you pay for and $0.02 worth of advice may not be worth taking.
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Re: KH Piston Clearance

Postby xlh59 » Thu Feb 15, 2018 1:26 pm

thanks for your reply wz507,

my intention to re-sleeve the one cylinder is basically because I want two identical bores on both cylinders and because this is a full restauration (it would be wise to have the option to redo the cylinders sometime again). I will try to keep things as original as possible, but I also want to have a technically perfect bike.
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