Topic: First Time rebuild on Hardtailed Craigslist find

[SWHonda]

So, about late 2015 I picked up a 1971 CB750 from a Craigslist add for cheap in Virginia. I got to cleaning it up and found a hole in the lower engine casing after I got the engine out. Three years later and a move, I'm finally getting down to rebuilding it along with restoring the frame, getting a new tank, and upgrading the front braking. I eventually went with getting a different engine that had more fixable problems, no welding required. I ended up with a 1978 CB750k engine that needs a new clutch, among other things. I just sold a bike that was gathering dust. So, I'm putting that money into this bike. I'm planning on doing a full rebuild of the engine and was wondering where to start. What I should go ahead and order? So that when I get the chance this weekend to take the engine apart, I can get this project done. I appreciate the help in advance. Will post pictures of the before and try and keep this up to date as I go.

[SWHonda]

Here are some pics of when I first got it.
And some more with the tank and seat gone and then finally the engine out of the frame.


Sent from my iPhone using Tapatalk

[SWHonda]

Made up a quick stand to get the newer engine off the ground and started cleaning. Probably won’t get to opening the engine up till this weekend.


Sent from my iPhone using Tapatalk

[SWHonda]

Finally had time to get into the engine. Tore down to the lower casing and I’m trying to decide if I need to crack the case. I can replace the cam chain tensioner without going any lower, and I’m wondering if it’s worth doing. Any thoughts? I’m planning to send the pistons and cylinder off to a machine shop to get measured and then see where this takes me. Any advice on powder coating the engine? I’m planning on sending it off to be done, this will also help influence whether or not I need to open the lower case.


Sent from my iPhone using Tapatalk

[Gurp]

Great start!!!!

[SWHonda]

Thanks, I’m trying to stay organized so reassembly is less of a pain.


Sent from my iPhone using Tapatalk

[SWHonda]

Dropped the cylinder head and pistons off at a machine shop with the measurements from the service manual today. I’ve been looking at Cycle X’s MLS head gasket. Anyone have experience with it? It’s $70 by itself. So, I want to make sure it’s a good investment. Or is it something more for the performance side of things.


Sent from my iPhone using Tapatalk

[slikwilli420]

MLS is definitely performance oriented and really not needed for a street bike with stock compression. If you go 836 or want lots of compression it is a good choice. I have the Cycle X one going on my race bike and have full confidence in it. If I was doing a mild street engine, I wouldn't bother.

[SWHonda]

Thanks for the info. I just got word back from the shop that cylinders just need a hone. So, I’ll just go with the normal head gasket.


Sent from my iPhone using Tapatalk

[SWHonda]

So good news and bad news. Bad news is that due to the engine having water sit in it, the hone didn’t get all the pits out. So, to the good news, I get to have more power, eventually. I’ve been looking at Cycle X’s 849cc kit and I’m definitely going to replace the studs, any advice on what else in the cylinder head needs upgrading to handle the bigger bore? I’m already replacing the primary chains, cam chain, and cam chain tensioner assembly.


Sent from my iPhone using Tapatalk

[SWHonda]

Finally found some carbs on EBay for cheaper than I expected and I finally settled on boring the head to just .50 over and getting the pistons to fit from Cycle X. The parts are in the mail and the machine shop will get the pistons to measure and bore soon after they get here. I’m going back and forth on trying to powder coat the engine myself or sending it out to get done. Any tips on powder coating in the garage or should I just fork out the cash to get it done by a shop?


Sent from my iPhone using Tapatalk

[PeWe]

MLS head gasket work fine if the mating surfaces are flat and have no scratches. I made the head and cylinder nice on a flat board placed on the kitchen table where I glued grinding paper, 2 A4 sized after each other. 240 to sand down the scratches, then 400 for final.
The good thing with MLS is no future need of re-torque. You can also open head again and reuse the gasket.

I have RCS  (rubber coated steel) base gasket in my K6 with billet block. Like the MLS but only one sheet. I made upper case surface good with the sanding paper, 240 + 400. No leaks here!

You must check if the MLS gasket rivets will be located between head and cylinder. They did on my 836. I hammered rivets flat and drilled small dimples on head and cylinder with a 8 mm drill for the rivets.

My K2 build got fiber gaskets. I re-tourqed head 4 times until it stopped to compress. I marked nuts-head with a pen to see if they moved when re-tighten. I'll see if it will leak. It got several o-rings that must sit correct. Late gasket with big 8 oil return holes, old head-cyl. 8 o-rings here that I hope did not jump up between gasket and head.

[SWHonda]

So, machine shop called and one of the sleeves didn’t bore out well. It had apparently been resleeved and was put in slightly off center. So, a new sleeve has to be ordered. The engine is apart and is ready to get all new chains and gaskets. Any advice on when to paint the engine? Looking give it a fresh coat all over.


Sent from my iPhone using Tapatalk

[754]

Suggest a used sleeve to them..cheap.
 I for one don't believe what they said, cuz usually they center on the existing bore, wherever that might be.