Topic: CB750 Motor rebuild... for dummies

[Terry in Australia]

Guys,
         Really intended to focus on the build with this thread. But I haven't posted any progress in a while and I felt that everyone following this deserved a progress update.

    My "non-CB750 life" interrupted my build-  I have to sell my home and relocate for my career. In order to keep the parts tidy I am re-assembling the motor, hand-tight. Then I am moving my parts to Mom & Dads barn until I can get settled and get back to it. Realtor tells me that cleaning the garage could help the resale value- 
 
    Silver lining is that anywhere I move to will have more CB people than my current area.

    I am happy to see that enough people are chiming in to keep the thread alive...I will be keeping an eye on it.

    Sincere thanks for all the help I got. It will not be wasted-I shall return!   Steve

Hurry back Steve, and good luck with the move! Cheers, Terry.

[SandwichEnthusiast]

So I'm finally down to the bottom of the engine, everything ripped out as far as it is going to get. So all I have to do is: check the oil pump, order all sorts of replacement parts, clean it, hone it, replace all the worn parts, reassemble it, tune it, and if I still have the energy ride it around.

The only things out of the crankcase that didn't get removed are:
- the bearing for the countershaft in the middle of the case
(I'm wondering about the effects of cleaning the engine on that bearing)

- the gearshift drum out to the neutral stopper plate
(I couldn't get the screw out off the stopper plate, somebody mentioned a specific term for what they did to lock that screw down earlier in this thread but i can't seem to find it.)

I managed to get the transmission countershaft out around the gearshift drum by taking off the countershaft top gear, then pulling the countershaft off the  bearing, then taking off the final drive gear and low gear, and then shimmying the rest out gently (I had it flipped completely around before I could get it out I think).

Additional musing:
removing the stopper pin from the kickstarter was super hard, I needed to squeeze it down with some vice grips and shimmy it out. None of the literature ever writes "this particular step may be a huge pain"

[bryanj]

Awlwrite Terry, Just cos i got a dyslexic keyboard and have to put the glasses back on to read the screen!!!

[paulages]

Additional musing:
removing the stopper pin from the kickstarter was super hard, I needed to squeeze it down with some vice grips and shimmy it out. None of the literature ever writes "this particular step may be a huge pain"

i had an unbelievably hard one recently.. see this thread: http://forums.sohc4.net/index.php?topic=29496.0
i ended up having to soak with penetrating oil, heat the case, wiggle the #$%* out of it with channel locks, and then eventually i got it up enough that i could get a screwdriver beneath it, prying up while twisting on the top with the channel locks. 

it sure made the next one seem easy. 

[Sweep]

So I'm finally down to the bottom of the engine, everything ripped out as far as it is going to get. So all I have to do is: check the oil pump, order all sorts of replacement parts, clean it, hone it, replace all the worn parts, reassemble it, tune it, and if I still have the energy ride it around.

The only things out of the crankcase that didn't get removed are:
- the bearing for the countershaft in the middle of the case
(I'm wondering about the effects of cleaning the engine on that bearing)

- the gearshift drum out to the neutral stopper plate
(I couldn't get the screw out off the stopper plate, somebody mentioned a specific term for what they did to lock that screw down earlier in this thread but i can't seem to find it.)

I managed to get the transmission countershaft out around the gearshift drum by taking off the countershaft top gear, then pulling the countershaft off the  bearing, then taking off the final drive gear and low gear, and then shimmying the rest out gently (I had it flipped completely around before I could get it out I think).

Additional musing:
removing the stopper pin from the kickstarter was super hard, I needed to squeeze it down with some vice grips and shimmy it out. None of the literature ever writes "this particular step may be a huge pain"

I had to drill out the screw for the gear mechanism as well as a couple of the screws for the countershaft bearing.

When you dismantle the shifting mechanism, shift forks/rod and remove the neutral stopper then the drum slides out the side.  I didn't bother with removing the bearings at the bottom of the case or removing my kickstarter because it was in good order.  I was careful about the cleaning and avoided the bearings with solvent.

[RRRToolSolutions]

Guys- I can't stay current with this thread, but I have noticed something I don't agree with -

Ring gap should always be checked in the hole it's going to live in upon assembly - always. Never assume they are correct. It's so easy to do and could save a ring geting folded and broken. You simply insert the ring into the cylinder using the piston and measure the end gap with a feeler gauge. If needed, a small flat file held in a vise can be used to increase the gap if needed. If the gap is already too big - you need to consider a bore/hone and new pistons and rings.

Regards,
Gordon

[754]

I second that.. leave nothing to chance..

 Double check, triple check.. the extra time can save a lot of pain..

Ring end gap on a new ring may tell you more than your self-measuring did..

[paulages]

alright fellas, now i have a question: where the hell do these dowels and seals go (the seals come in the emgo gasket kit, but not it the Z1 kit)?:


i remember removing them, and the fiche shows them here i believe (parts #2 & 3):

...but i can't figure out where the hell they actually fit. i definitely put dowels in any dowel holes before installing the cylinders and head. looking at the pictures i have on my computer, it makes perfect sense that they fit here, right?:


..but when i was at the shop, i tried fitting them to a '71 engine i had apart and there seriously seemed to be nowhere for them to go.

to boot, i got the damn thing bolted up and everything before realizing i had left them out. really don't want to waste a head gasket, let alone completely disassemble all the top end again. on assembly i had four bolts strip, or rather four previously helicoiled threads come loose.


seal all the way on the left  (in the first picture) came in the seal kit, but i don't know where it goes either.

[Patrick]

The earlier 750s didn't have as many dowels or seals. That skinny dowel at the upper right hand corner looks like it goes with a side cover. The clutch cover or alternator cover, perhaps.

[paulages]

The earlier 750s didn't have as many dowels or seals. That skinny dowel at the upper right hand corner looks like it goes with a side cover. The clutch cover or alternator cover, perhaps.

i'm not worried about the skinny dowel, it just happened to be in the photo. thanks, though.

[bryanj]

If you havent run the engine you should be OK with the gasket but without those seals it will piddle oil. if there was 4 of the big rings i would suggest exhaust gaskets!

[RRRToolSolutions]

There was a production change in 1974 and those extra seals around the studs were added. I know this because I had ordered the parts and was really confused during assembly that they would not work. The factory shop manula describes this as a mid-1974 model change. Mine was about 200 below the serial number so it's the same as what you have.

Regards, Gordon

[Kevin D]

I found this service bulletin #42 in the library. It talks about the dowels, orings, early model, later model. My K1 had just the 2 orings at the supply studs, center rear. When I put it back together I'm going to do it like this: think I'll have a different HG and 8 more orings without the dowels, and 8 less chances for head gasket oil weep.

http://data.sohc4.net/SB750/750_42.pdf

Paulages, what are the numbers on that unidentified oil seal? A point seal is 30-42-8, kicker 18-29-7, clutch lifter 13.8-24-?? or 14-24-5.

[paulages]

thanks for finding me that TSB. explains it perfectly. i guess i'll pull it back apart today, as painful as it is. i guess they added those seals for a reason.  stupid '76 motor.

Paulages, what are the numbers on that unidentified oil seal? A point seal is 30-42-8, kicker 18-29-7, clutch lifter 13.8-24-?? or 14-24-5.

i'll have to get the numbers on that seal at my shop, but the seals installed are: final drive shaft seal, points and stator crank seals, tach drive seal, kickstart seal, clutch center seal, and shift shaft seal.

[paulages]

by the way, has anyone else had any problems with the emgo gasket kit? it's more complete, but the valve cover gasket doesn't fit. it's a hair too big.

[paulages]

If you havent run the engine you should be OK with the gasket but without those seals it will piddle oil. if there was 4 of the big rings i would suggest exhaust gaskets!

bryan-- i was trying to figure out what you meant by this...i get it now. the big ring being the one on the left, right? no, it's definitely a square seal. i'll take the meaurements off it and get back.

[RRRToolSolutions]

Paul, I for one will only use Honda gaskets with one exception - the cylinder head gasket due to the big-bore requirement for a larger one.

I darn sure won't use another Athena gasket set period.

Regards,
Gordon

[paulages]

Paul, I for one will only use Honda gaskets with one exception - the cylinder head gasket due to the big-bore requirement for a larger one.

I darn sure won't use another Athena gasket set period.

Regards,
Gordon

i'll sure never use the emgo gasket set again (this is the first time i've used one) even if it does have more parts than the other, as it seems poor quality. i figure what seems poor to the eye is probably worse in use.

[paulages]

the seal in question is 33mm O.D., 25mm I.D., 4mm tall.

[Patrick]

According to the parts fiche, that goes in your starter clutch.

[paulages]

bingo. i didn't pull the stator off of the crankshaft, which explains why i couldn't remember where it went. 

[KB02]

Here's a link to one of my current posts that might fit well in this thread:

http://forums.sohc4.net/index.php?topic=31212.0

[HondaMan]

Well done guys, I'm looking forward to seeing your progress! The good thing about the legendary CB750 engine is that it is dead simple to work on, and to bring back to "as new" condition. I've recently (in the last 12 months) built 2 engines, one stocker, and one "competition", and so all I reckon you'll need parts wise for a "rebuild" is the following:

Full gasket set (CycleX, $59.00)
Set of Piston Rings (Rusty Riders $30.00)
Cylinder Hone (buy the tool to fit your cordless drill, around $10.00)
Heavy Duty Tsubaki Cam Chain (Z1 Enterprises $28.00)
OEM cam chain tensioner, wheel, and guide (Z1 Enterprises $61.00) 
Engine seal set ($20.00 from Rusty Riders)
New OEM Primary Chains (Terry Quail, $70.00 per set)
New NGK Spark Plugs ($10.00 from your nearest auto parts store)
New points ($10.00 from Rusty Riders)
Engine Enamel ($10.00 from your nearest auto parts store)

There's probably one or two items that I've forgotten, but as you can see, for around 300 bucks you can do a full "rebuild" that a shop wouldn't do for under 1000 bucks. Spend the other 700 on good quality tools and better quality booze, and give yourselves a pat on the back! Cheers, Terry.

OK, Terry: where's this "Rusty Riders" place? I'm gonna need new 2nd oversize pistons and rings soon, and wristpins...

[paulages]

Here's a link to one of my current posts that might fit well in this thread:

http://forums.sohc4.net/index.php?topic=31212.0

i think there was already discussion in this thread about removing the stator. luckily, i have air and an impact wrench, so removing them isn't a problem for me, i'd just rather not do it if there isn't a reason. the starter clutch is working fine, so i left it alone.

[paulages]

Well done guys, I'm looking forward to seeing your progress! The good thing about the legendary CB750 engine is that it is dead simple to work on, and to bring back to "as new" condition. I've recently (in the last 12 months) built 2 engines, one stocker, and one "competition", and so all I reckon you'll need parts wise for a "rebuild" is the following:

Full gasket set (CycleX, $59.00)
Set of Piston Rings (Rusty Riders $30.00)
Cylinder Hone (buy the tool to fit your cordless drill, around $10.00)
Heavy Duty Tsubaki Cam Chain (Z1 Enterprises $28.00)
OEM cam chain tensioner, wheel, and guide (Z1 Enterprises $61.00) 
Engine seal set ($20.00 from Rusty Riders)
New OEM Primary Chains (Terry Quail, $70.00 per set)
New NGK Spark Plugs ($10.00 from your nearest auto parts store)
New points ($10.00 from Rusty Riders)
Engine Enamel ($10.00 from your nearest auto parts store)

There's probably one or two items that I've forgotten, but as you can see, for around 300 bucks you can do a full "rebuild" that a shop wouldn't do for under 1000 bucks. Spend the other 700 on good quality tools and better quality booze, and give yourselves a pat on the back! Cheers, Terry.

OK, Terry: where's this "Rusty Riders" place? I'm gonna need new 2nd oversize pistons and rings soon, and wristpins...

mark- i got my stock size rings from them via ebay. word to the wise though: the picture in the auction showed three piece oil rings and they gave me one piece rings.