Author Topic: Top head knock pins (Read 1196 times)

theslayedsaint · « **on:** January 19, 2015, 07:03:02 PM »

So I think I've already answered this qustion for myself but would like to make sure I'm right. I installed the wrong size knock pins on the top side of my cylinders, there just a little shorter then the ones I should have installed, but are the same circumference size. I'm thinking it's fine and that's its more a guide. Right?

-1974 CB750
-the two # 12

seanbarney41 · « **Reply #1 on:** January 19, 2015, 07:14:51 PM »

The real question is What happened to the correct ones? If you have switched the correct #12's with the #11's you may have some serious oil leaks at the base gasket.

theslayedsaint · « **Reply #2 on:** January 19, 2015, 07:41:32 PM »

No they where really badly damaged, so I bought a few different dowls but they didn't have those and I forgot that and installed them thinking that it was the same because tht fit. So do you think these are ok? Just a little shorter should be fin right

seanbarney41 · « **Reply #3 on:** January 19, 2015, 07:54:46 PM »

I would think too short is okay, as long as they are not so short that they allow the head to wobble around.

theslayedsaint · « **Reply #4 on:** January 19, 2015, 08:04:24 PM »

so... i just kinda understood what you where trying to say before! and no i want to scream. if i have to pull the head again for some dumb dowel. so i measured the ones i have left, and they are 18mm. and now i don't know what the hell to think these should be 22mm or 15 mm if they where 22mm i would know that there the top part and just move on no big deal. also if i tried to put the #12 where the #11 go wouldn't it not sit flat?

theslayedsaint · « **Reply #5 on:** January 19, 2015, 08:19:30 PM »

ok again after some thinking and running around pulling my hair out! i think i'm back to "good" heres a post that seems to fit my point and i feel like i should be good.
http://forums.sohc4.net/index.php?topic=89613.0

seanbarney41 · « **Reply #6 on:** January 19, 2015, 08:20:05 PM »

I don't know...depends on if your cylinders' holes that fit the pins had enough extra clearance for longer pins. You might get lucky, or you might not...

Much better to double check now than to have the bike all back together, running...and leaking. I always check the fit of these pins without gaskets in place, put the cylinders on and make sure they fit onto the case nice and flat. If not, they can be trimmed with a grinder, files, etc. Once they fit without a gasket, you know you will have ample clearance with the gasket installed. Do the same thing when you put the head on the cylinders.

theslayedsaint · « **Reply #7 on:** January 19, 2015, 09:13:39 PM »

Ok,
yes that all makes sense and i'm trying to learn as i go to not keep going forward without making sure everything is prefect. but its not working out so well right now. so at this point what i know is. i used the wrong dowels on the top half they should have been 18mm and what i put in was 14mm. so what do you think is it worth pulling the bolts off? i cant find the 18mm ones any where so i'll have to try and clean and sand the old ones. or do you think that those are more just for guiding and should be fine. i mean i don't want to undue my new studs and have to retorque them but if its a big deal would rather do it now then when its on the bike. and if thats the rout to go, is puling the bolts off and retightening them bad?

PeWe · « **Reply #8 on:** January 20, 2015, 02:52:06 AM »

Different years different lenghts. Verify that the pin is not too long and head will leak a lot.
My K6 had 18mm cylinder-case, 18mm cylinder -Head. K2 had 15mm and 22mm according to CMSNL
The 8 special with fat o-rings? They are 12mm

But I have found 22mm in my engine, between cylinder and case. I measure the depth on both side just for sure to verify the hole is deep enough.
Head and mating cylinder surfaces can be decked and the dowels must be checked and maybe need to be shorter

seanbarney41 · « **Reply #9 on:** January 20, 2015, 03:18:30 AM »

This is the kind of detailed assembly that you HAVE to do to have a successful build on one of these engines. This is not a chevy small block, it is basically a 1960's Grand Prix engine....

theslayedsaint · « **Reply #10 on:** January 20, 2015, 07:50:49 AM »

Thanks PeWe,
My qustion now remains I know I put the wrong pins in the top.
I also know that there off by 4mm. Should I disassemble and change them?
And if so are my MLS gaskets able to be reused?

And seanbarney41 yes I understand that being detailed is the way to go! This is my first buil and I've been stressing over everything and trying to make sure to check and double check. However it is my first build so somthing may just happen. But thanks for the advice

bjbuchanan · « **Reply #11 on:** January 20, 2015, 08:13:23 AM »

You gotta pull them only if they are longer. Shorter don't bother. If you can't say 100% that they are shorter than necessary then pull the stuff apart. It will leak right from startup if you don't.
Iron worker had this problem too in his otherwise meticulously documented build.

MLS gasket will be fine to reuse after confirming the pins are what you need

theslayedsaint · « **Reply #12 on:** January 20, 2015, 08:43:56 AM »

I'm 100% that the top head ones are shorter. How you say? Because I bought 3 of the pins and can measure the 3rd one and its smaller then the one I should have used. And I'm 99% sure that the bottom ones are right because I have the 18mm ones left, so only thing I could have used was the shoter 15mm ones...

theslayedsaint · « **Reply #13 on:** January 20, 2015, 09:12:17 AM »

But hell if pulling some nuts off and putting them back on makes me feel more at easy may as well do it again.

theslayedsaint · « **Reply #14 on:** January 20, 2015, 01:30:40 PM »

So any thoughts on if I pull the head I can still reuse both the head gaskets? I'm planing on pulling the head off and installing old pins if the gaskets would be fine to reuse.

Vinhead1957 · « **Reply #15 on:** January 20, 2015, 01:55:38 PM »

Never reuse gaskets! The nature of a gasket is compressibility . It absorbs all the imperfections on first use and after things heat up they get baked into position. When you take things apart after use they no longer have their original compressibility.

theslayedsaint · « **Reply #16 on:** January 20, 2015, 04:58:02 PM »

yeah, the engine is being rebuilt never been turned on yet. still you wouldn't reuse?

Vinhead1957 · « **Reply #17 on:** January 20, 2015, 05:04:04 PM »

Now that is a grey area. Feeling lucky then by all means. Surfaces all look good even more so. Personally I'm frugal and would chance it but accept what i get

seanbarney41 · « **Reply #18 on:** January 20, 2015, 05:12:24 PM »

I would re-use them, as long as they don't stick and rip

theslayedsaint · « **Reply #19 on:** January 20, 2015, 06:09:54 PM »

Ok.. Here we go I'll pull the head and make my self feel better.

theslayedsaint · « **Reply #20 on:** January 20, 2015, 06:32:59 PM »

Pulled it and funny enough the bottom pins are 18mm also. But I did a little measuring and they fit. So I guess I'll close it up with the 18mm ones again. Even though it said it should be 15mm. Seems to have been working before.
Thanks for all the help guys

PeWe · « **Reply #21 on:** January 22, 2015, 03:45:58 AM »

My 2 knock pins cyl-head were shorter last time. Most important that the pin do the job to make sure that head is locked to the cylinder sideways in correct position.
8 Special pins with fat o-rings not used since the new head gasket (Cometic fiber) has no hole for them, neither has Cycle-X MLS.
Older head gaskets had wider holes. The 8 inner for oil transportation. I have a new 65mm gasket from Yamiya that has the wider holes. The head is not leaking yet. Only 1500km after last head lift.

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Author Topic: Top head knock pins (Read 1196 times)