Topic: CB 750K 5/7 Build "Slowlog"

[Sohc85]

Hi, new to this forum and have been waiting to build a CB750 for some time now. So i found a project for sale, its basically a bunch of parts.. so it might be a challenge, but why no. The parts included a lot of new stuff including a 836cc big bore kit with sylinder and wiseco pistons and head gasket. And the price for all this was basically less then just the new parts, so i that that at least i would get rid of any spare time i have . I do have another CB750F1 that is slightly modified, but only overhauled the top part of the engine on this one.
So given that I only have a little experience with these sohc engines I thought that a build thread would be a good way of getting tips and knowledge. Has worked very good on other forums where i had a couple of car builds.

So on to the build... what is the end goal? I really don´t know. I think a replica 70s CR750, but that might change with time and/or funds . First up is building an engine and then il get to work on the rest. Having a good engine is probably a good idea no matter what "style" i end up with. I do fear that the build is going to take a fare bit of time, but winters are long here, and bike seasons are short....
Here is my current working CB btw



Started last week picking all the parts up, sorting basically getting to grips with whats missing.




So most of the mechanical bits are there, missing some bolts and tank, seat. But the original tank and seat i won't be using anyway. I also got a spare parts engine. The frame is a K7 and engine a K5. The spare parts engine is a K7. Of the new bits are;

836cc sylinder
wiseco pistons and head gasket
Dynatek coils and timing plate
New cam with longer lift (haven't checked specs on this one, its called "web cams")
Adjustable cam gear
Valve springs and retainers
All new valves and guides
points cover and clutch cover (honda parts)
engine stand ( handy bit of kit)
Two gasketkits

So I split the case and my plan is to make sure everything was in order because the previous owner did not know what had been done by the one before that. And  I think i have two of most bolts and misc. I found some good news, and some bad.



Bad news is that the camtowers and caps do not match, so from what I've heard I'm guessing eBay next, despite that i am changing the cam.
The lower crankcase has been welded, at some point, probably after the bike tipped over i guess. But it seems like cosmetics and can probably be tidied up a bit.

Good news is that crank, crank and rod bearings seems to have normal wear so its all usable, just change all bearings. (could post a picture of those as well)

Up next i have to read up on inspecting the gears. I was told they had been overhauled.

So on the internet and order parts i guess...I am trying to find out if I need stronger rods and hardened rocker arms due to the big bore kit and new cam. Also start to find out what kind of bearings i need for crank and rods, plastigauge them and start putting things together. I will also check the two chains and get new tensioners for them...

[Don R]

 Looks like you're on track. Take your time and enjoy the process.

[Sohc85]

Some progress. Got used cam towers coming, promised to be good ones. Got a full list of parts needed, and basically all  bearings are going to be replaced, rod bolts and nuts, studs and bolts, cam chain tensioner and primary chain tensioner.
Probably going with CycleX as they have a lot of upgraded parts. For the bearings i can source them locally (Honda parts).

The cam i got with all the parts turned out to be a Web Cam CX1( cycleX part) with probably explains the unmarked valve springs. Iḿ guessing those are heavy duty springs that apparently are needed with this cam. How it will work with a 836cc kit.....?




So got to check the transmission, oil pump and crank today. All within spec. However I do need to replace the outer bearing on the mainshaft as it did not sound great. Found the parts available at yamiya750 after reading a couple of threads here about mainshaft ball bearings being as "rear as unicorn teeth".

The only "fault" i could find was the mainshaft 2nd and 3rd gear that had some chipped teeth, no more than 1mm on the ends. Probably a little hard to see on the picture..... in the red circle....

I really don´t think this matters, so I'm not getting it replace, or if someone has any input?

So after reading a bit more i don´t think i will replace the rods with hardened ones, as the original ones should be fine according to several threads here. not sure about hardened rocker arms but it might be a good idea as the cam, as far as i could figure, is hardened.

So next step is getting rid of all parts in the two engine half's and getting them cleaned and then starting to get it back together. I am thinking of using a local business who can do this by using proper equipment, think they use ultrasound cleaning, and they are cheep as well.

O, and a disclaimer I forgot in the first post, sorry for any grammatical errors, not my primary written language....

[Sohc85]

So was in the prosess of inspecting the top end of the engine when I noticed something.. I do have several heads but only one that is worth using. Where the Oil control orifice is located I noticed that there was a obvious differences in the two of the heads. take a look at the pictures.

This one seems to be like the genuine Honda part


This one however does not look like the genuine ones I have found on honda parts sites. Its bronze, has a different shape, and it seems that the hole is somewhat smaller. That would then suggest that the top end is getting less lubrication, and the oil pressure might be higher? I have heard that there are two types if these Oil control orifice´s.!?



So the question is, are these things hard to pull out and should i be bothered? any and all input is welcomed.

[Sohc85]

So.. a new day of wrenching on the engine. Plan was to completely strip down the engine so the case halves and head could be delivered to machining, cleaning. Got there at the end but not without a couple of hiccups.

Top half almost ready, two of the cylinder studs where a pain...


When looking at the top half of the crankcase i noticed a chip next to one of the "cylinder sleeve holes". Got a bit concerned. As seen in the picture it is not a huge bit missing but this is the surface where a gasket is going to be and this would make the gasket not pressed between two surfaces. This is however on the "low pressure side" and the cylinder sleeves does fit deeper than this surface. Does anyone know if this should be filled in/repaired?



Next issue was a borken cooling fin on the head.. I guess this is not a big deal but as it would not cause any leaks, but it probably does not improve cooling .. I dont´t think I am going to be to concerned by this...


next thing is a bit.... weird ... I real can't seem to get this one.. been searching the forums and looking int the workshop manual.. When I took out the valves I saw that the valve guides on the exhaust side where different from the intake side. But after looking at the workshop manual it almost looks as if the guides are mounted the wrong way around... New ones are going in but anyway I did not manage to find out what´s going on here

Intake side, all good


exhaust side.... and no valvstem seals.....


Last I, think, I found out whats up with the new valves, guides and springs  that came with the bike as new parts.
I was wondering if this was a kit for a DOHC engines as i had 16 retainers.. but I do think this is the "Bee-Hive" kit form cyclex. The new springs are have a smaller diameter at one end and they are taller. So no inner spring is needed, as I´v read on the cyclex webpage. Less weight is always good..

[Sohc85]

So as this is a "slow build log", i finally got some time to work on the engine.. Had a few issues with the top, so i got hold of a good second hand one and it should be here in a week or so.

Also got a box of goodies in the mail from Japan(yamiya750.com)... should be alle the gaskets bearings for the bottom end (but as usual, i bet I have to order more since I have probably overlooked something)


So i got the engine disassembled, filled in the small chip with some "chemical metal" something like JB weld. And sanded it by using glass plate to make sure it would be as leveled as possible. Also cleaned up all the threaded bolt holes, a lot of gasket material in them....




Got the engine cases cleaned up ready to start putting everything tighter. First I used a degreaser and pressure washer then dried it with compressed air. next step was using a gasket remover water and air again. Finally I used parts clear fluid and compressed air, tearfully to blow through oil passages making sure they where free of debris.


I then started with the transmission shafts. changing all the bearings there. Got everything of easily, and by putting the bearings that go in the engine case and the shafts that need new bearings in the freezer over night, they all want on with few issues.




One bearing I do not know how to get of is the one one the primary tensioner... Anyone know how to remove this one? I can't seem to find anything in my workshop manual! It is the one that sits between the sprocket and the clutch bucket.. Are these two parts just pressed together?




At least I managed to do some work finally! next up are the journal bearings and plastigauge, just waiting for the plastigauge to arrive..

[tulsah]

Where did you happen to find the replacement bearings with the machined groove in the outer race?

[Sohc85]

Where did you happen to find the replacement bearings with the machined groove in the outer race?

http://www.yamiya750.com/index.php?main_page=index&cPath=246_21_250_52