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Engine case replacement.

Tristan

CB750 Enthusiast
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Nashville
When I bought my 78'K she came with a cracked case. It leaks very little oil out of it. Old owner said the chain broke and had its way with the upper and lower case. He tried to fabricate a patch and got it running but still leaking. (I can't wait to see this patch) I just purchased a new to me case on eBay and about to undertake my first motorcycle engine. Being the case that surrounds a ton of the bikes heart I purchased a lot of parts to replace while I have the heart exposed.

Bare block case with cylinder studs - eBay $174.74 free shipping!
Versah complete gasket kit - eBay $108
Complete engine Allen stainless bolts - eBay $48
K&N flywheel puller - eBay $8 (looked like I need it and it was only $8)
NGK spark plugs - Old Bike Barn $11.80

That's what is in the air or on the ground headed to my house now.

I am ordering all of the oil seals, valve rubbers, new fuse box assembly (original owner didn't get the recall memo. Two blown burned fuses in less than a month) and I think that's all I need for a decent rebuild. The engine is strong and doesn't need a rebuild but again since it will be all taken apart might as well. Right?

I have had a ton of trouble locating 1978 cb750k piston rings! Everybody has up to 76' but 0 for 77' and 78'!
Please help!

Another question is my cam chain tensioners, do I need new ones if the originals are in place? I have 23k miles on it if the odom is correct. I guess it could have 123k miles too but the way it runs I think it's just 23k.

Are there any special tools I need? I have all of the basic tools (all sockets, wrenches, pliers etc), feeler gauges, impact driver, soon to have flywheel puller. Anything else needed?

That's all for now. I start the tear down this Sunday 1/20/13. I will take pics of my entire build.

Thanks in advance for all of your tips and tricks that you can give me.

Tristan
 
Engine case picture

My ebay purchase of the bare block case. image.jpg
 
Make sure you have a shop manual, or access to one. The biggest thing you will have to check is main bearing clearance, you may need new main bearing with the switch to the different set of cases. Thats where the manual will come in in helping to determine what bearings you need depending on the markings of the crank and the cases. You will need some green Plastigage to check bearing clearance. You should have the cylinders honed for the new rings so you wont use oil and the rings will seat properly.
 
the gasket kit should include the oil seals and valve rubbers. there are no special tools for these motor. then again i'm a machanic so i have ton's of tools LOL.
i would replace the cam chain tensioner anyways.

if your gonna throw out your old case's, i will take them.
 
I dont know who you have checked with to look for rings......Service Honda still lists stock size rings as available but I dont know what they actually have for stock available. If you have it apart I would put in a new cam chain along with the rollers on the chain adjuster.
 
at least a heavy duty cam chain for sure. dont mix the bearings. keep all the shells intact and on the same journals. bearings and rings are cheap compared to doing it twice. decarbonize, and hand lap the valves. inspect the starter drive clutch under the rotor. make sure your oil passages to the top end arent blocked.
 
Looks just like my 77,same color. These bikes are fast, mine will outrun my frnds 1300 vtx & any harley that has tried.Not happy with finding parts for 77-78 though. I think its cool when most harleys in our mc. club even out at 110 -120 & I have to slow down so they can keep up.The vtx prob has more top end but he doesnt have the nerve & I wont throttle another mans wife, I mean bike.
 
Finally started the tear down. Here are some pics.

So far the only real tricky part has been actually getting motor out of frame with just my own two arms.IMG_7768.jpgIMG_7765.jpgIMG_7773.jpgIMG_7778.jpgIMG_7786.jpgIMG_7787.jpgIMG_7788.jpgIMG_7789.jpgIMG_7790.jpg
 
Oh how could I forget, the damn carbs were harder than crab to pull out. The bible says remove the carburetors in one line! Psshh easier said then done. I destroyed the clamps on the hoses between carbs and air box.
 
More progress..

I took the rocker arms off, got the cam shaft out, lifters and all 5 million cylinder stud nuts (really 22 nuts) off. [Note: There are 4 hidden nuts, you will need a thin walled 10mm socket or a light tap with a hammer to the long extension. They are under the rubber seals in the middle of the head under the cam.] Removing the head from cylinders wasn't too difficult. I decided to clean the bulk of buildup off of the pistons heads while in cylinder sleeve. I figured it would be easier since they were stationary. They cleaned up nice with a soft wire brush and simple green. Next I removed the cylinder sleeve case. (Not sure what that is called). Then... phew I took all of the bolts that connect the upper and lower case. (The case is what I need replaced.) I thought after taking the bolts out the case would magically separate. Not the case at all. haha. So I think next I am going to remove the clutch and whatever is on the other side, the alternator innards. Here are some photos of the work so far.

IMG_7805.jpg IMG_7811.jpg IMG_7810.jpg IMG_7809.jpg IMG_7808.jpg IMG_7807.jpg IMG_7802.jpg IMG_7803.jpg IMG_7804.jpg IMG_7806.jpg IMG_7814.jpg
 
Clutch doesnt need to be removed and neither does the alternator to split the cases. The shift linkages and the bearing support on the alternator side of the engine is what is holding the cases together. Look carefully at how the shift linkage comes apart because there are several springs and spacers that have specific orders.
 
Dirtdigger I don't completely understand. I removed all of the springs and what not linkage. I could not get off the piece with 4 screws that connects to the bearing. Is there a trick to them? I destroyed my impact driver bit trying.
 
The piece with the four screws is what is holding you up from getting the case split. Rounding off the screws is a common thing and the screws can be a pain to remove. Impact driver is about the only way to get them off. You may need to heat them a little to help break the screws loose. If you have the phillips part rounded off in the screws your next option would be to take a dremel tool or similar and cut a slot into the head and use a straight blade impact driver. Make sure you are hitting the impact driver hard enough because gentle or light taps on the driver do little more than round the screws off.
 
I got 2 out of 4 by heating them up and impact driver. Two things, dreading the Dremel (don't have one and more than likely about to own one) and where do I find the screws to replace them? This is my only transportation and want to finish quickly but do it right. Thanks DD
 
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