Board index Flathead Power-Technical Questions, Answers, and Suggestions Morthodites-"Non Factory" Rubber O-Rings instead of Gaskets

Rubber O-Rings instead of Gaskets

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Post Thu Mar 06, 2008 1:49 pm

Posts: 141
Location: USA
I am contemplating the idea of machining up some stroker plates and it seemed like a good idea to consider machining grooves into the plates ,top and bottom for inserting some type of rubber or synthetic O-Rings instead of gaskets.The stroker plates would be steel between aluminium and cast iron.To me there are a multiude of benifits but I am going to ask your opinions there may also be a equal or even more surpassing reasons not to consider this.Tell what you think,Thanks,Tom :D

Post Thu Mar 06, 2008 2:05 pm

Posts: 1654
main issue I can think of is maintaining the height of the barrels correctly. presumably you would need a comparable groove in the barrel base or top of case respectively? I'm not too familiar with the details but that's my understanding. Seals would need to be suitably heat-resistant spec as well. Sounds a good approach otherwise.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Thu Mar 06, 2008 2:52 pm

Posts: 2688
Location: Los Angeles, CA
Stroker plates make your cylinders longer. In doing so your intake manifold no longer fits correctly. Do it right and get stroker pistons.
Last edited by Chris Haynes on Fri Mar 07, 2008 10:32 pm, edited 1 time in total.

Post Fri Mar 07, 2008 12:10 pm

Posts: 591
Location: Crewe, Great Britain

Hi all,

There's an easier and perfectly mechanical way to fit O rings on your plates, just have a 45 degree chamfer made on both sides on the ID, that will provide a nice triangular tore between the plate and the cylinder spigot where you O ring can sit in and still be compressed. OK only if you don't have deep reliefs for the rods on the cylinder walls


Post Sun Mar 09, 2008 7:14 am

Posts: 141
Location: USA
Thanks,guys I will keep your ideas in mind.My use of stroker plates in this case applies to K models.I have several sets of the short K model cylinders and my intention is to use stroker plates with an increase in stroke to get up to around 55 cubic inches so that anyone in the future would be able to replace the pistons if needed with standard K model pistons instead of having to obtain special made Expensive stroker pistons.Being that K model gaskets are hard to come by I thought it would be beneficial if one were able to elimimate the use of the old gaskets and use O-rings that hopefully would be of a superior design and readlly available at a cheaper price from almost anywhere.It seems that if the moderen bikes are doing this that it would be an improvement.

In reference to the need to modify the intake manifold, it's my understanding that once the short K model cylinders(45 cubic inch) have their height increased by 3/8 to match the later KHK cylinders, I should be able to use any of the later KHK manifolds. Please correct me if I'm wrong. It won't be the first time, and sadly, won't be the last. Thanks again for your help. Tom :D

Post Sun Mar 09, 2008 12:33 pm

Posts: 591
Location: Crewe, Great Britain

All K, KK, KH or KHK manifolds are the same, -40 part number, old WLDR/WR and maybe some U as well...

On taller cylinders, the copper compression rings just sit a bit more out, that's all.

Also, most K/KH pistons you'll find today are made to the KH pattern. Same pin height from top but the bottom is radius relieved to clear the wheels. So no need to worry about fitting K unrelieved pistons in a KH!!!


Post Mon Mar 10, 2008 6:30 am

Posts: 141
Location: USA
Patrick,I have always wondersd how it came to be that Harley designed the K model pistons in the 45'' version to have the short piston skirts that would later by some chance be just right for the later 55'' version .It always seemed to me that they knew they were going to increase the stroke but for some reason held off a few years.Do you think it had to do with some restrictions governing race classes?Again ,Thanks for your thoughts,Tom. :D

Post Mon Mar 10, 2008 12:01 pm

Posts: 591
Location: Crewe, Great Britain

Hi, Celticlodge,

No, K pistons were longer, part # 22251-52...

They were updated with bottom radius for the 54 KH, part # 22251-52A. When the stock of -52 ran out, they just sold -52A as replacement for all K models. My 54 parts book only list the -52A as available, $12.00 with pin and rings, the -52 is there, no price, replaced by the latter.

I don't know of anybody that does "real" K pistons, all the replacement I've seen are the KH -52A variety...

Last edited by thefrenchowl on Tue Mar 11, 2008 11:58 am, edited 1 time in total.

Post Mon Mar 10, 2008 3:27 pm
Pa Site Admin

Posts: 5843
Location: Ohio USA

Don't know if this information will be valuable to you folks or not but when I opened up my first 55 KHK top end, I found the rear piston had lost a skirt somewhere along the line. Pa

Post Mon Mar 10, 2008 6:47 pm

Posts: 141
Location: USA
Patrick,Thanks so much for clearing this up for me I have been confused about this for some time.Very enlighting ,the truth makes much more sense .Thanks again,now maybe I won't have those nightmares waking up , wondering.'"Why,Why did they do it".Tom. :D :D

Post Mon Mar 17, 2008 12:32 pm

Posts: 575
Location: devon,england
hi k model base gaskets are availiable from the motorcycle storehouse catalogue ,i know as ive just bought a pack ,.....of ten, regards jib
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

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