KH Piston Clearance

Production K Models

Re: KH Piston Clearance

Postby Ferrous_Head » Fri Jan 26, 2018 9:47 pm

As I said - I don't use their pistons. But it's true most manufacturers son't warrant race parts. I've generally found a lot can be done with them if you approach them in the right manner. Simply demanding warranty on a failed race part probably won't get you anywhere. But supply them with a forensic analysis of what happened to their parts in service and many will offer advice and help. At the end of the day they know people soon talk about parts that fail on a regular basis. If Wiseco's recommended clearances resulted in a lot of seized pistons you can bet the Internet would soon be full of "Their product is Sh*t stories". Many years ago it was all we used in the 900 Kawasaki's we ran. Never had problems with their big bore kits. Cheaper and better than stock parts. We used their specs from memory.

But if you feel that you can second guess the manufacturers and do better - by all means, do so.
"I know only too well the evil that I propose, but my inclinations get the better of me."
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Re: KH Piston Clearance

Postby GuS » Sun Jan 28, 2018 5:46 am

If any of you remember the late mr. Steph from the FHP board. He had a lot of knowledge. He shared his method of checking requiered clearance. He measured the piston expansion when boliling piston in water. Reason was that difference in piston temp vs cyl temp would be same as cylinders in room temp ws boiling hot piston. I have since used this method to find how much bore clearance to give. And also to check bore clearance given by manufacturer.


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Re: KH Piston Clearance

Postby Geodoc » Mon Jan 29, 2018 6:18 pm

wz507 wrote:
I looked back through some old notes I made and see that Wiseco recommended fitting at 0.0025”, Enfield recommended 0.0035 – 0.004” and the race engine builder who recommended 0.004-0.0045” (I misquoted this earlier when I said this was Enfield’s recommendation). I would never think of running this forged piston at the Wiseco recommendation of 0.0025”, because Wiseco lacks experience with this particular engine design, it’s intended end-use and it’s operating temp. I guess the only way to really know the lower limit of fit is to start snugging them in and determine at what point things start to tighten up (but that doesn't sound like much fun to me).


Just spoke to Bruce at Enfield Racing to confirm piston clearance before taking the barrels & pistons to get bored. His recommendation for a street bike use (I stressed that it was not for racing) installation is .004" - 0045". Since he's been the 'end user' for these Wisco pistons in K Model applications, going to go with .004". Did notice that on the boxes that the pistons came in did in fact have a clearance recommendation printed below the P/N - .0025" as mentioned above.

As an aside, his recommendation for head bolt torque (no gasket) is 45 ft. lb. Currently tending toward using the solid copper gaskets that Erick sent with the original KHK cylinders to replace the K ones that it had w/ stroker plates.
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Re: KH Piston Clearance

Postby Simon » Tue Jan 30, 2018 12:58 am

I would be curious to know what pop-up if any these pistons have?

I've always found those copper gaskets a bit of a curiosity. Were they cut to otherwise work around scratched or marred mating surfaces, or to add valve to head clearance without machining valve pockets in the heads? I've always just used silver/copper paint after prepping the surfaces, and not had any issues.
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Re: KH Piston Clearance

Postby Geodoc » Tue Jan 30, 2018 2:05 am

As a part of final assembly, the plan is to use some plasticine to measure the piston to head and valve to head clearances and then decide on whether or no on the gasket. The squish clearance in an OHV engine is best set at about .040" from what I've fiddled with (mostly Guzzis). Same for the "squish" area that's between the piston and head on a flathead?

Simon wrote:I would be curious to know what pop-up if any these pistons have?

I've always found those copper gaskets a bit of a curiosity. Were they cut to otherwise work around scratched or marred mating surfaces, or to add valve to head clearance without machining valve pockets in the heads? I've always just used silver/copper paint after prepping the surfaces, and not had any issues.
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Re: KH Piston Clearance

Postby EKHKHK56 » Tue Jan 30, 2018 10:12 am

I purchased them originally for possible situations where clearance above open valves is off due to extra head surfacing, etc. I've always torqued the heads in 3 sets, 45, 55, 65 lbs final with threads lightly lubricated. These head bolts are same dimension as small block Chevy which run 65 last round. Always worked, no issues. No combustion leaks. Erik
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Re: KH Piston Clearance

Postby EKHKHK56 » Tue Jan 30, 2018 10:16 am

The pistons, while flattop, do stick up out of the bore significantly stock.
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Re: KH Piston Clearance

Postby wz507 » Tue Jan 30, 2018 11:28 am

Simon wrote:I would be curious to know what pop-up if any these pistons have?


The compression height of the Enfield piston is the same as the stock Harley piston, ~ 1.24”, so piston height at TDC will be identical with both pistons.

Enfield and stock piston on common wrist pin
LR Enfield and HD Piston on common wristpin.jpg
LR Enfield and HD Piston on common wristpin.jpg (122 KiB) Viewed 12005 times


EKHKHK56 wrote:I purchased them originally for possible situations where clearance above open valves is off due to extra head surfacing, etc. I've always torqued the heads in 3 sets, 45, 55, 65 lbs final with threads lightly lubricated. These head bolts are same dimension as small block Chevy which run 65 last round. Always worked, no issues. No combustion leaks. Erik


Regarding head torque, 65 ft-lb has been used successfully for decades, so proven to work fine. In my mind this is an astronomically high clamp force to hold a piece of aluminum on the cast iron cylinder. The SBC has 5 bolts/cylinder to secure a stiff cast iron head to a cast iron block and deform a head gasket. The K head has 8 fasteners to clamp an aluminum head with no gasket. I think 45 ft-lb is more than enough clamp force to adequately secure the K model head, and lowering the torque will have the added advantage of minimizing bore distortion.
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Re: KH Piston Clearance

Postby EKHKHK56 » Tue Jan 30, 2018 3:53 pm

The .004+ sure seems like a bit much for such a small bore non competition. You will want to warm it up slowly until those skirts grow or they can crack. Perhaps their alloy is that dense. Wiseco would know. However I would use Gus's method of bringing one to operating temperature, 205°, and measuring the skirt then just to see what is going to happen. Only take 5 minutes. Gus always has great ideas and is one of the finest flathead, etc craftsman I know. Erik
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Re: KH Piston Clearance

Postby EKHKHK56 » Tue Jan 30, 2018 3:59 pm

I've never heard of head bolts being torqued so lightly. A similar fine thread alloy head on cast iron block arrangement uses 105 lbs. 20 lbs more may be needed maybe not. Ive always used it. You're not talking very much. The amount of pressure a 20 pound weight puts on something with one foot lever. Erik
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