Author Topic: K0 / K1-K2 Fork Piston Differences (Read 1462 times)

nomadwarmachine · « **on:** July 27, 2020, 08:57:57 AM »

Rebuilding my 201xxx CB750K2 and have discovered how difficult it is to locate the correct fork piston (51442-319-000). I have found aftermarket K0 pistons (51442-300-000) and wanted to ask whether there are material differences between the two parts.

Could I use the K0 with the repro fork tubes I am using with my lowers, or should I continue searching for the correct piston?

754 · « **Reply #1 on:** July 27, 2020, 10:09:14 AM »

Do you have a picture of any of the parts ?

nomadwarmachine · « **Reply #2 on:** July 27, 2020, 10:23:08 AM »

Unfortunately not. All I have is the K1-K2 piston on the existing parts. I have been hunting for a replacement and found one in Europe matching the K0 part. Trying to determine whether that will work before ordering. Looks like the fork design was changed at K0 # 1039119, so it may not work -- probably not worth the international shipping to take a chance...

bryanj · « **Reply #3 on:** July 27, 2020, 10:41:30 AM »

Look at the parts list and see what else changed at that number

nomadwarmachine · « **Reply #4 on:** July 27, 2020, 11:04:06 AM »

Good advice. Looking at the wholesale changes to the fork parts at K0 # 1039119 it looks like a bad bet to presume that this part will fit. Thanks!

69cb750 · « **Reply #5 on:** July 27, 2020, 11:36:09 AM »

https://www.ebay.com/itm/1972-72-HONDA-CB750-CB-750-LEFT-FRONT-SUSPENSION-FORK-SHOCK-STANCHION-STRAIGHT/114141580945?_trkparms=ispr%3D1&hash=item1a935e4e91%3Ag%3A9CYAAOSwnFleYuv%7E&enc=AQAFAAACcBaobrjLl8XobRIiIML1V4Imu%2Fn%2BzU5L90Z278x5ickkAgU0umhwUTmgTFbE5cu7zeQcmJEvGUMjy3DCikC1rvR%2F3b4AE%2F0DwizVXQsPr5L0fmy4tMTGamw%2BBFem5TXn3KokQRUvlpcxvAhew23BqkEwkEja3pLkUUI8%2BuAYjhdOx%2BdTog5CU3M4YbzdRhPawi56BEU1lODyuzxWX7VrIVpjszObjgdIIzG%2F%2FE8ZvsP6SxkQOlVJVyU1X6onIGF8WiefOUKHBwg%2B6f4vdgCdvY%2FErFnSZVD%2Bmc2lrbWuEy5%2BN4YOqv%2B7Qc9Zn4M0cg%2FZSROWv80vaA%2BfW%2BXZPiRpTaj1LA%2Ba2SZXAnzkEG6JPGfyAXhwMxaUd4Yz3nOe3q%2FYrVoGIL14glczS%2FUC7v2KGQFsVSNva5DjvvT2rfWTzcPRqmG7IzMhyYEt83CM7TEe%2BKhl%2B%2FQS3AEdgyxDmw%2B%2Biq%2FyehhFIWM6ACHBsKy2C0fpnrKVvf35hCGUYi7AHZcr6yOKdebXBbVK5KClVJsKTT81PCm49EcGHPcPDU0Tac4McqEMILKA5GUzYspdp1X6Ja1xCcAOyWz4bPrH7bLCxuLEXGeaTC0CIoiVl2mUi1QvYEm07U78%2FwnVAYKCx0HZxi7MP%2FXtqAt0QKWMCK8NK186ElbDZNzW1UBonqOhPvDSlw9%2BPdqS1ETEyQ9VUEUHV0LNRdcse3yZaH6DVKyquuel8mDfiJMyZ6s6TVZAoQSHj%2FZuh4IRKkZJwbGuxUz4jysbSt%2F1nHpZvaEAfrH00%2FYTAgQ3T%2F9r2UwJ3fm7guQ2C83BIKSyvEZGYSkz%2B0PVMg%3D%3D&checksum=114141580945b276f7cd9e8d41dda8eb8a23ee25f538&LH_ItemCondition=4

754 · « **Reply #6 on:** July 27, 2020, 12:10:01 PM »

The reason I asked for a pic was , I am thinking a bushing that snap rings on tube..... but maybe he means the rod inside , a pic even of someone else's part may help.. I think I have single 71 72 leg that I can part out.

And while at it tell us what country you are in.. help us to help you , I am in Canada..

nomadwarmachine · « **Reply #7 on:** July 27, 2020, 12:11:40 PM »

It's the "piston" bushing. Happy to add a photo. Do folks upload their photos to the forum or post remotely?

I am in Los Angeles, California.

69cb750 · « **Reply #8 on:** July 27, 2020, 12:51:15 PM »

Piston is bottom part

nomadwarmachine · « **Reply #9 on:** July 27, 2020, 01:44:01 PM »

That's it! https://www.cmsnl.com/honda-cb750k0-four-1969-usa_model14346/piston-front-fork_51442319000/

Also need the "collar" valve which is 51443-273-000 on the diagram: https://www.cmsnl.com/cb750k2-four-netherlands_model14367/valve-damper_51443273000/

754 · « **Reply #10 on:** July 27, 2020, 03:39:38 PM »

Do you need one or two ?

nomadwarmachine · « **Reply #11 on:** July 27, 2020, 04:31:23 PM »

Just put in an order for two NOS pistons, so I only need the collars now -- if you are breaking down the forks, I would gladly take both off of you assuming they are in good condition!

754 · « **Reply #12 on:** July 27, 2020, 04:48:53 PM »

No , as I said i only have one fork, inside condition unknown.
BtW what happened to your parts, ? If forks are worn , sometimes can be tightened up by making these parts oversize..

nomadwarmachine · « **Reply #13 on:** July 27, 2020, 05:15:07 PM »

If the collar is in good condition, I will take that off your hands. Both my piston & collar look like they saw the business end of an angle grinder (see photo).

If you have it, would also take the snap ring that is second from the bottom of the form the steel colored wire ring that holds in the piston (pointing to position in photo). My piston was practically fused to the fork tube and I was surprised to see there was no snap underneath!

I have had this bike for 20 years and rode it around the USA for 3 months in 2002 without a single breakdown (other than a broken fuse that doesn't count). Before leaving I disassembled the front end to discover that somebody had assembled a hybrid fork from a K0 lower and K2 parts, and I encountered the strange fusion of piston & tube w/grinding marks at the bottom of the right. The damping still worked OK, and I did not have the $$ or the parts, so I swapped the fork seals and hoped for the best before returning and swapping the K0 lowers for correct K2 lowers. Now that I can really get inside the forks, I see that the last 40K miles have not made things worse, and the bore of the swapped K2 fork lowers looks good, but I would like to reassemble with fresh parts or parts within the wear limits!

Happy to PP you the $$ & shipping. Can PM my address.

69cb750 · « **Reply #14 on:** July 27, 2020, 05:20:09 PM »

Quote

My piston was practically fused to the fork tube and I was surprised to see there was no snap underneath!

No oil, check condition of lower leg.

nomadwarmachine · « **Reply #15 on:** July 27, 2020, 05:44:19 PM »

Lower leg bore is smooth and even with no obvious damage. The original bore was from a K0 (with the squared fork seal lip) that I swapped for K2 lowers some years ago. The fused piston predated the new lowers, which have always been filled with oil and appear to have no damage from the parts you see above.

Marty23 · « **Reply #16 on:** August 30, 2023, 07:30:10 AM »

I have only question related to front forks and don't want open new topic. I started with some work on my CB750K2.Bike come from Germany.

Question is if I have correct part configuration for K2 model? According to drawing which I have K2 front fork was without bottom pipe and without

bottom plug on the case. My parts are closer to K3 but I don't have small spring on bottom pipe.. Martin

HondaMan · « **Reply #17 on:** September 01, 2023, 09:02:44 PM »

Quote from: Marty23 on August 30, 2023, 07:30:10 AM

I have only question related to front forks and don't want open new topic. I started with some work on my CB750K2.Bike come from Germany.

Question is if I have correct part configuration for K2 model? According to drawing which I have K2 front fork was without bottom pipe and without

bottom plug on the case. My parts are closer to K3 but I don't have small spring on bottom pipe.. Martin

The K2 bikes came with K1 forks until around 3/1972 builds, then the forks changed to be like K3 forks.
Generally speaking, if the fork tube has the separate lower valve ring (like your picture), then it is the "early" K1 version. If the lower end of the tube is crimped inward with no replaceable outer valve ring, it is the later design that was used from K3 thru K5 (and some K6) bikes.

Knowing this will help you to locate parts a little more easily, if nothing else.

trigger · « **Reply #18 on:** September 04, 2023, 04:48:48 PM »

Quote from: Marty23 on August 30, 2023, 07:30:10 AM

I have only question related to front forks and don't want open new topic. I started with some work on my CB750K2.Bike come from Germany.

Question is if I have correct part configuration for K2 model? According to drawing which I have K2 front fork was without bottom pipe and without

bottom plug on the case. My parts are closer to K3 but I don't have small spring on bottom pipe.. Martin

A German 750 K2 would be the same as the UK 750 K2 which had 300 K1 forks up to the middle to late 1973 and then changed to 341 forks. The european and UK CB750 K2 was produced up until 1975

Marty23 · « **Reply #19 on:** September 05, 2023, 02:30:54 PM »

Thanks for your respond. Can I get somewhere IPC drawing for this specific configuration? I get parts list from CMSNL but K1/K2 fork there is without

bottom pipe. And K3 fork with bottom pipe looks a bit different then fork on my photo. My bottom pipe has not small spring on bottom.

I will need front fork pipes for my bike and I am almost sure that K2 will fit but for interest I would like to see IPC drawing with my exact

configuration.

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Author Topic: K0 / K1-K2 Fork Piston Differences (Read 1462 times)