KR Heads

Racing K Models

KR Heads

Postby wz507 » Mon May 01, 2017 4:55 pm

The subject of KR heads has come up in several different threads on this forum, and although the forum information on the topic is rich, it is spread thinly throughout many threads. Was hoping to consolidate more of it here under a new thread focused solely on KR heads, so hope people with KR head information will chime in and post.

For my own curiosity, I asked in a previous thread how many different KR heads were produced by the MoCo, and sifting through that thread and others come up with 52R, 59R, 60R and 69R. Is this correct and complete or are there many more? Also, our forum experts teach that not only were there these major part numbers, but also the single integers 1 through 7 stamped on the heads that indicate something about that particular combustion chamber? Here’s a teaching moment for someone in the know – did the integers 1 through 7 correspond directly with head part #’s or were these integers separate indicators that were totally independent of the part #’s?

Another thing I’d like to see are images of the unmolested combustion chambers of the various heads to see firsthand how the shape progressed over time and cam development. I’ll start it out by posting the ubiquitous chamber shown by Jerry Branch in the 1965 Cycle World article by Gordon Jennings on KR development, along with an image I have but don’t recall where it came from. I’ll also post an image from the starcain thread about “KR Parts and Questions”.

Jerry Branch KR Head.jpg
Jerry Branch KR Head.jpg (64.95 KiB) Viewed 21251 times


starcain 52R head.jpg
starcain 52R head.jpg (19.97 KiB) Viewed 21251 times

So a couple of images and that is enough to start me off on a whole new series of questions. Note that the combustion chamber in the starcain image starts beyond the middle head bolt from the IN side toward the EX side of the chamber, whereas in the Branch and unknown sourced image the combustion chamber, or as I'm fond of hearing Erik call it, "the snowcone", starts above the middle head bolt. And when you start the shelf beyond the middle head bolt you can't create a nice symmetrical snowcone. So to those in the know, was the poorly shaped snowcone an early factory shape or that of a privateer? Also what occurred along the path as the heads transitioned from integer 1 to integer 7.

The Jerry Branch image also raises another question, in that he is showing a stock K model head and saying it has to be converted into the shape of the finished head shown next to it. I thought the KR heads came ready to use as cast with the proper shelf angle and combustion chamber depth already established. Is that true or false? Did you actually have to start with a stock head, weld it in, then carve out the correct pattern?

Directly related to the discussion of combustion chamber shape is the image below found in the Competition Racer Manual for KRs, showing the shelf angle for a #7 head and cautioning that "Location of Shelf Angle Very Critical". I always wondered why this was in the manual and figured it must mean one of 2 things. Either it was an instruction of how to modify your existing head to this conformation, which never made sense to me since I thought the KR heads would already be made to this specification if it was VERY CRITICAL, or it was a cautionary statement that the shelf angle is very critical, your head already looks like this, and don't even think of trying modify it or you will loose power. So gentlemen, why was this image included in the manual - was it to assist in performing a Jerry Branch job on a stock head or was it a cautionary statement by the MoCo to inform that "we've got this" don't worry about it and don't mess with it? Does anybody know the vintage of the Competition Racer Manual this image came from or the approximate vintage of the #7 head?

KR shelf angle.jpg
KR shelf angle.jpg (37.89 KiB) Viewed 21251 times

Another question I have relates to the brass or bronze spark plug insert used in KR heads. I appreciate that the insert makes the thread robust and affords effortless plug inspections as often as one would like, but always wondered about the change from a 1/2" plug in standard K models to the 3/4" reach plug employed in KRs. I see in the manual that KRs were shipped with a Champion N60-R, which is a very cold plug to begin with, but with the additional notation that "These spark plugs are for warm-up and break in only". Thus I suspect they needed a cooler plug yet for racing and that such a cool heat range plug did not exist in 1/2" reach so they required a 3/4" reach to access such cold plugs?

That's enough for now, and hoping people have additional images, insight and information to share on this interesting topic. Thank you.
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Re: KR Heads

Postby ambike » Mon May 01, 2017 9:00 pm

The " hottest " Champion in that series is the N62-R, followed by the N60-R.

Some charts show the 60 Champion equivalent to an NGK 9, but the Champion could be a bit hotter.

Running Champion plugs on a half-mile track or less, I'd race a Harley V-twin or an Aermacchi CR or ER with no hotter than an N57-R.

The Sprints ( especially the short-stroke 250 ) with a tight squish require an R type gap.

It should be understood R means retracted, not racing.
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Re: KR Heads

Postby thefrenchowl » Tue May 02, 2017 2:48 am

In short, race plug don't exist in 1/2 reach...

You can only find 3/4 reach race spark plugs.

Don't confuse cold plug and race plug, they are not the same...

Hence deeper insert for proper race plug.

KR heads were cast as KR heads, they are not K moded heads. They are easilly recognised by the xxxxx-60R or whatever raised -xxR casting number between the fins on the valve side (it's in the outer mould, not stamped after the cast...)

Factory might spend 10 hours doing a works head for Joe Leonard, and maybe 1/2 an hour for a privateer head...

Hence the drawings in the manuals to tell you as far as you can go to improve your privateer heads.

1 to 7 are the number of variants for the std flat piston KR. then 8 for the dome piston KR

I believe there are only 3 or 4 different castings in all for these 8 heads. The 1 to 7 or 8 then indicates hand finished contours.

To tie up with the other thread on K heads... All these valves have clearances between the valve at full opening and the roof...

KR valves need: inlet 120 thou, exhaust 80 thou.

So when you measure depth, take account of that...

K and KH heads are fitted as cast, no work at all in them.

KK and KHK heads have the inlet roof touched up.

The tool is dead simple: a valve with a tip brased on, 120 thou.

Install head on cyl, put a stopper that will limit the lift to that of the valve, 375 thou and turn tool with lecky drill to clear the roof.

Any other K or KH head configuration is PO, not factory...

Patrick
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Re: KR Heads

Postby 55panman » Tue May 02, 2017 10:46 am

Patrick, Why do you need .055 more clearance for a KR flathead intake valve then for a OHV engine? Flathead with no pushrods and short operating length should have far less chance of floating valves than and overhead with flexing pushrods. Or does the radical shape of KR cam profile cause tappet to float over the nose? Or is that to give more clearance for flow around back side of valves? Thanks in advance.
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Re: KR Heads

Postby wz507 » Tue May 02, 2017 11:18 am

thefrenchowl wrote:KR valves need: inlet 120 thou, exhaust 80 thou.
So when you measure depth, take account of that..

Thanks for your valuable knowledge and insight in the above post.

Curious about the 0.080" clearance over the EX valve. The KR Competition Racer manual specification (shown below) calls for 0.110" over IN and 0.040" over EX, which makes sense to me since the IN airflow can benefit from the extra clearance, but EX side is a different story since blow-down occurs at much higher pressure, thus not benefiting similarly from the large clearance. I suspect this is why the over-valve clearance spec on the IN is large and the EX clearance spec is only ~1/3 that of the IN. So interested to know if you may have misquoted the over-valve clearance or have some other information that steers you to the values quoted that are different than those quoted in the Racer manual. Thank you.

KR valve to head clearance.jpg
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Re: KR Heads

Postby thefrenchowl » Tue May 02, 2017 11:22 am

Latest latest last of the Mohican heads 120 inlet 80 exhaust!!!!

Your document is circa 1959...

Panman, clearance between top of valve and roof of chamber, NOT tappet clearance"""

KR for that is .006 in, 010 ex

Patrick
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I'm the one who has to die when it's time for me to die so let me live my life the way I want to...
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Re: KR Heads

Postby EKHKHK56 » Tue May 02, 2017 11:34 am

Yes the clearance above the open valve is for flow. Joe told me the factory paid Tom Sifton and Len Andres $1K in 1953 money everytime they developed one more horsepower. So the fellows at those race camps were spending late nights on the dynos trying to wring all the power they could from the KR. No doubt they had access to H-Ds best parts as they both owned dealerships however factory backing $ wise was very limited.
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Re: KR Heads

Postby wz507 » Tue May 02, 2017 12:00 pm

thefrenchowl wrote:Latest latest last of the Mohican heads 120 inlet 80 exhaust!!!!
Your document is circa 1959...
Patrick

Ok, that's cool.

To continue the extrapolation of what/why/when regarding the KR heads etc.....

If the Competition Racer manual is circa 1959, and since it shows the final #7 head shelf schematic for a flat top piston (FTP) KR, it would follow that all the head development, relating to FTP KRs that the factory divulged, occurred between 1952 and 1959? Presumably the 60-R head incorporated all the learnings occurring up to that point in time and all 60-R heads are #7? And sometime from 1960 to 1969 the clearance specs you quoted were discovered?

But the real question is "what's a Frenchman living in England doing knowing about the last of the Mohicans"? Well I guess it was the French that were fighting afterall.
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Re: KR Heads

Postby 55panman » Tue May 02, 2017 12:07 pm

Thanks for the replies. Yes, I know it's not tappet clearance. I should have been more specific. I was thinking in terms of valve head to obstruction clearance in this case the combustion chamber roof and in OHV the piston or valve to valve at TDC, in case of valve float. Thanks again for info. I am hoping to put a KR together from pieces I've collected with J cams I got from Joe George (RIP). This will help setting it up. Thanks again
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Re: KR Heads

Postby starcain » Tue May 02, 2017 12:46 pm

If the Competition Racer manual is circa 1959, and since it shows the final #7 head shelf schematic for a flat top piston (FTP) KR, it would follow that all the head development, relating to FTP KRs that the factory divulged, occurred between 1952 and 1959? Presumably the 60-R head incorporated all the learnings occurring up to that point in time and all 60-R heads are #7? And sometime from 1960 to 1969 the clearance specs you quoted were discovered?

wz507, For what it's worth, I have a set of 60-R heads that are # 6
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