Author Topic: 1973 CB 750 Rebuild. (Read 3561 times)

Grizzy · « **on:** December 27, 2017, 05:10:03 PM »

Just finished getting my work area ready, has some heat at least!

Bike is not running but turns over freely. Going to take apart just about everything. Starting with good intentions...labeling everything that comes off and putting into baggies or containers. Also lots of pictures along the way

Grizzy · « **Reply #1 on:** December 27, 2017, 05:11:25 PM »

I have gone thru all the Hackaweek videos on YouTube for the 73 750 rebuild, going to be a big help

Stev-o · « **Reply #2 on:** December 27, 2017, 06:06:44 PM »

What do you plan to do with the engine?

Have you tested compression or given it a leakdown test?

Grizzy · « **Reply #3 on:** December 27, 2017, 06:44:00 PM »

Bike has 17k miles, new rings for sure, everything else depends on what I find.

MauiK3 · « **Reply #4 on:** December 28, 2017, 08:56:56 AM »

I have a headlight can from a 73.

MauiK3 · « **Reply #5 on:** December 30, 2017, 07:20:58 AM »

Sorry, left out it's available if you need it. I have some other 73 pieces too.

Grizzy · « **Reply #6 on:** December 30, 2017, 12:05:42 PM »

Thanks Mauik3, nearly have everything taken off and will make a list of what needs to replaced soon

Grizzy · « **Reply #7 on:** January 07, 2018, 05:24:59 PM »

bike now in about 100 baggies and plastic containers...well labeled!

Starting engine teardown, so far things looking fairly good

Grizzy · « **Reply #8 on:** January 12, 2018, 02:58:24 PM »

I was feeling pretty good about what I saw on the top end and then pulled off the drain pan. Screen was covered with debris. A lot of it feels like silicone sealer.

Stev-o · « **Reply #9 on:** January 12, 2018, 07:15:31 PM »

Looks like someone blackened the oil pan!

Grizzy · « **Reply #10 on:** January 13, 2018, 11:30:08 AM »

Black oil for sure, been sitting a while. When I dragged a magnet through the crud a fair bit stuck to it,

Grizzy · « **Reply #11 on:** January 14, 2018, 01:40:03 PM »

I have removed 14 of 16 cylinder studs using a double nut on top and vice grips near the case. I’ve tried heat on the studs, lubricant (wd 40), tapping with a hammer and no luck. Really worried I’m close to breaking one off.

Any suggestions out there?

Something better than wd40?

Thanks

Medyo Bastos · « **Reply #12 on:** January 14, 2018, 02:12:33 PM »

pb blaster

Stev-o · « **Reply #13 on:** January 14, 2018, 03:01:50 PM »

Quote from: Medyo Bastos on January 14, 2018, 02:12:33 PM

pb blaster

+1. Or Kroil. And heat.....

Grizzy · « **Reply #14 on:** January 14, 2018, 03:33:33 PM »

I have used heat on studs, afraid to heat the case

Grizzy · « **Reply #15 on:** January 15, 2018, 09:20:11 AM »

Any opinions on leaving the 2 frozen studs and using 14 hd on the others?

I figure breaking one off is the worst ‘option’, maybe just accept that 2 will be the originals

JoeCooley · « **Reply #16 on:** January 15, 2018, 06:41:40 PM »

Quote from: Grizzy on January 15, 2018, 09:20:11 AM

Any opinions on leaving the 2 frozen studs and using 14 hd on the others?

I figure breaking one off is the worst ‘option’, maybe just accept that 2 will be the originals

I wouldn't recommend it. Use heat on the case around the studs. The aluminum should expand quicker and help release. You can also try heating it and applying candle wax to the base of the stud. The wax will go into the threads. This is an old school trick a machinist friend showed me. If all else fails, cut the stud shorter and have a nut welded on. Then get a socket and big breaker bar.

Grizzy · « **Reply #17 on:** January 15, 2018, 06:54:23 PM »

Good tips, shortening the stud makes sense, getting a lot of twist right now and fear any more force will break it....going to give it a try, thanks

JoeCooley · « **Reply #18 on:** January 16, 2018, 03:34:34 AM »

Quote from: Grizzy on January 15, 2018, 06:54:23 PM

Good tips, shortening the stud makes sense, getting a lot of twist right now and fear any more force will break it....going to give it a try, thanks

That's pretty much what will happen. I snapped a couple when I did mine. Just remember to apply heat to the aluminum, not the stud. The stud will get hot but aluminum conducts heat better. You don't want the stud to expand. Do circles around it with your torch to evenly heat it. Just be carefully not to melt the case. You should be fine with a propane torch but oxy/acetylene will get hot enough to damage the case.

calj737 · « **Reply #19 on:** January 16, 2018, 05:09:52 AM »

If you have to resort to welding, weld 2 bolts onto the shank of the stud perpendicular to the stud, making a T. Turn the T and the stud will turn right out. The heat introduced from welding the stud will loosen all the rust.

Grizzy · « **Reply #20 on:** January 17, 2018, 03:57:55 PM »

Woo Hoo! Got the last 2 cylinder studs off!

I tried using wax, didn’t work right away but after heating and tapping with a hammer they finally came

Thanks for all the suggestions

JoeCooley · « **Reply #21 on:** January 17, 2018, 05:07:26 PM »

Quote from: Grizzy on January 17, 2018, 03:57:55 PM

Woo Hoo! Got the last 2 cylinder studs off!

I tried using wax, didn’t work right away but after heating and tapping with a hammer they finally came

Thanks for all the suggestions

I'm glad it worked out for you. I have a set of low mile 78K pistons if you need them. Worth beer money... It'll give you a small bump in compression...

MauiK3 · « **Reply #22 on:** January 21, 2018, 08:46:54 AM »

I have some 29,xxx mile pistons and pins, good shape, came out of my K3 750, was running. I put in .5mm over pistons.

Grizzy · « **Reply #23 on:** January 21, 2018, 10:56:26 AM »

Got them rebuild project blues!

Having a hard time splitting cases so I double checked number and location of bolts. Found where a upper case bolt should have been is GONE!

The cases have been welded together, just in front of the front sprocket. Chain must have come off and put a hole in cases and it was welded over.

Bike was really dirty when I got it you couldn’t see the weld through the gunk. It isn’t running and I planned taking cases off when I started and painting them, didn’t do a detailed cleaning.

Time to come up with plan B

Stev-o · « **Reply #24 on:** January 21, 2018, 11:38:54 AM »

Wow, that's a new one. You sure it's not JB Weld, a common fix for broke case.

My plan B would be throw in my spare motor....but you may not have one, yet?

Grizzy · « **Reply #25 on:** January 21, 2018, 12:17:59 PM »

Could be, found set of cases on eBay under $100, looks like plan B

Grizzy · « **Reply #26 on:** January 27, 2018, 03:28:01 PM »

Got a set of cases for a cb750E on eBay from mrmonkeypaws. Weird name but excellent deal, just $85 with shipping. Cases look good, just need some cleaning and painting

Grizzy · « **Reply #27 on:** February 03, 2018, 02:14:02 PM »

Buying a bike that isn't running is risky, and it looks like I got bit.
Two broken rocker arms and 4 valves where the stems are mashed up enough they wouldn't slide out...had to grind down a bit with a dremel. Weirdest is that the exhaust valve stems have no seals, just seals on th intake. The valve seats look pretty good and I'm replacing the rocker arms, valves and seals hoping a lapping job will make all right again!

calj737 · « **Reply #28 on:** February 03, 2018, 03:26:35 PM »

If your valves were mashed, I would anticipate needing new guides. And then recut the seats.

Grizzy · « **Reply #29 on:** February 03, 2018, 03:30:52 PM »

Your advice is sound and I may end up there after seeing how the new valves look

MauiK3 · « **Reply #30 on:** February 03, 2018, 06:20:11 PM »

I have some K3 stuff available, cost would be little more than shipping.
Steve

Grizzy · « **Reply #31 on:** February 04, 2018, 10:06:09 AM »

Any chance you have a camshaft? Those broken rockers have ruined the one in this bike

Grizzy · « **Reply #32 on:** February 04, 2018, 10:17:39 AM »

MauiK3, Just saw your list on the For Sale forum, several items I would be interested in. I need to put a single list together, will contact you when I have that. Thanks!

Stev-o · « **Reply #33 on:** February 04, 2018, 01:08:08 PM »

I suggest having a qualified machinist inspect your head and make recommend exactly what work it needs. This is not an area where you want to cut corners

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Author Topic: 1973 CB 750 Rebuild. (Read 3561 times)