Author Topic: Icefire's 79 CB650 Project (Read 5911 times)

Icefire · « **on:** February 16, 2015, 08:55:30 AM »

Well after rebuilding a 1980 CB900 and most recently a 1981 CB750 I have decided to try tinkering with a SOHC .
I came across a 1979 CB650 that the PO said the head gasket needed to be changed which was evident with the oil stain on the outside of cylinder #4. He was able to start it up as it was in a shed and around minus 10c but it was revving quite high.
After a few days thinking about it I went back, purchased the bike and brought it home.

Icefire · « **Reply #1 on:** February 16, 2015, 09:05:03 AM »

Once I got it secured on the lift I did a compression check which had surprising results.
Cylinder # 1 - 120
Cylinder # 2 - 120
Cylinder # 3 - 0
Cylinder # 4 - 0
After removing the head cover the evidence was clear, the cam snapped at the cam sprocket. Looking at the cam journals it had been wearing for quite a while.

Trad · « **Reply #2 on:** February 16, 2015, 09:26:19 AM »

Crazy it was running like that. Good luck with the build.

Restoration Fan · « **Reply #3 on:** February 16, 2015, 09:30:45 AM »

Ouch! Well that would certainly explain the no compression on cylinders 3 & 4!

SOHC4 Cafe Racer Fan · « **Reply #4 on:** February 16, 2015, 09:33:02 AM »

Holy crap. Well, so much for the cam.

Assuming you are going to proceed with a full tear-down of the engine, Dynoman makes a 674cc kit specifically for the CB650 and you can use the stock cylinder sleeves; see the bottom of the page on http://dynoman.net/engine/pistons/dp-CB550.html

The good news is that you have a 1979 to start with. The frame is pretty similar to the 550 frame; in my opinion the 80-82 frames are fugly. Like the 550, the 79 frames have great geometry and the bike is inherently lighter than the 750. With a big bore kit and some porting work, you will have a punchy little sportbike.

Icefire · « **Reply #5 on:** February 16, 2015, 11:55:01 AM »

yes now for the hard part ......trying to locate a head, head cover with rocker assembly and a cam.

$:-\$

SOHC4 Cafe Racer Fan · « **Reply #6 on:** February 16, 2015, 12:23:32 PM »

Not that hard to find. Troll CL for parts motors. ALSO check the forums classifieds. Lots of 650 parts.

SOHC4 Cafe Racer Fan · « **Reply #7 on:** February 17, 2015, 10:03:10 AM »

Icefire,

I sent you a PM response. I think you just missed a 650 part-out in the classifieds, but I'm sure there will be more to come. I am not sure where you are located but it might help to know, since you may be close to a member who has what you need.

Icefire · « **Reply #8 on:** February 18, 2015, 07:01:59 PM »

Thanx for the PM, I was able to come across one a few hrs away from me. The fellow called me wanting to purchase the king/queen seat I had up for sale and during our conversation he mentioned he had a CB650 parts bike.
Going to trade a few CB750 parts for the complete bike.

Notice the dual front disc brakes on this one!!

SOHC4 Cafe Racer Fan · « **Reply #9 on:** February 18, 2015, 07:18:06 PM »

Quote from: Icefire on February 18, 2015, 07:01:59 PM

Thanx for the PM, I was able to come across one a few hrs away from me. The fellow called me wanting to purchase the king/queen seat I had up for sale and during our conversation he mentioned he had a CB650 parts bike.
Going to trade a few CB750 parts for the complete bike.

Notice the dual front disc brakes on this one!!

GREAT deal!! The duals discs should swap right over and another 79 frame, too!!

jordanp · « **Reply #10 on:** February 19, 2015, 11:17:11 PM »

Quote from: Icefire on February 18, 2015, 07:01:59 PM

Thanx for the PM, I was able to come across one a few hrs away from me. The fellow called me wanting to purchase the king/queen seat I had up for sale and during our conversation he mentioned he had a CB650 parts bike.
Going to trade a few CB750 parts for the complete bike.

Notice the dual front disc brakes on this one!!

Just gonna throw out that those forks have a leading axle, and won't be nearly as compliant as the standard axle placement forks...

rb550four · « **Reply #11 on:** February 20, 2015, 09:12:56 AM »

Sometimes you can find used parts,projects and information here
http://www.hondacb650.com/
Seems allot of the members here are also there,but some aren't.

Wittom is a member on both and has a curious habit of finding and parting out 650's.

So I'm guessing that the trade bike that you'll be getting for parts is an '81 because of the dual f brakes. Is your plan to rebuild the 79 engine still? I would build the later model engine because of better parts availability. I think I remember that the heads are different. The intake and carb spacing is on the 79 is the odd size out of all the production years....as I recall.
Perhaps a 650 guru could chime in on this so's I don't give bad information.

curemode2002 · « **Reply #12 on:** February 20, 2015, 01:16:56 PM »

Yes the intake spacing is different from 79 to 80-82. The 80-82 have the better head in my opinion (according to some the flow more air) but the 79's are pretty good themselves. I just like that the carb boots and carb setups are easier to find for the 80-82 heads. Wittom is great to work with by the way I have purchase a few parts from him for my 650.
Also when putting the top end back together there are two orings installed with the head gasket if you smash them or put RTV on them it can starve the cam journals of oil. That is my gues on your snapped cam.

Icefire · « **Reply #13 on:** February 20, 2015, 02:42:03 PM »

The frame is a 1979 but have not checked the vin number on the motor yet. Could be possible that the fork and wheel assembly were swapped out over the years hence the dual disc brakes.
The plan is to pull the cam and head from the parts bike to use on my 79 as long as the motor is a 79.
The parts bike motor is seized so until I actual break it down I am hoping the head, cam and rockers are still in decent condition, there are 32,000 Kms on it.
There are many scenarios to look at as the frame on my 79 had the tail chopped off by the PO where the parts frame is still stock.
The plan is to go down to pick it up this week coming, as long as the weather holds out.

Icefire · « **Reply #14 on:** February 20, 2015, 02:54:44 PM »

I just came across a 1978 CB750K parts bike with 3 motors on Kijiji. Spoke with the guy and looking at picking it up tomorrow to use for a future project.

Restoration Fan · « **Reply #15 on:** February 20, 2015, 03:23:41 PM »

No, honey. I don't have a problem! I could quit buying these things any time I wanted.

SOHC4 Cafe Racer Fan · « **Reply #16 on:** February 20, 2015, 05:41:06 PM »

You got a bad habit there!

Doggie · « **Reply #17 on:** February 20, 2015, 07:37:08 PM »

I'm picking up a 1980 CB650 tomorrow for $199 complete. Might be able to help with some parts for you.

Doug

Icefire · « **Reply #18 on:** February 22, 2015, 04:06:31 PM »

So I picked up the 1978 CB750K yesterday after some intense negotiating

and got the lot home. Going through it, there is one motor 1978 that runs ( 3025373 ) the original motor 1978 that is complete ( 3009300 ) but at this point will probably need a rebuild and the third motor 1974 ( 2350975 ) that looks complete also. The tires are actually in new condition which is a nice plus and the frame is in great condition for the age.
Still have a few boxes of parts to go through yet to see what is there but looks like I will be able to get a complete bike out of it all on a future project.
I will be doing a road trip tomorrow to pick up the CB650 parts bike and hopefully start working on the top end of the 79 this weekend coming.
Will post a few photos of it once I get it home.

Retro Rocket · « **Reply #19 on:** February 22, 2015, 07:55:36 PM »

Icefire, would you be interested i selling one of those 78 engines or a complete 78 bottom end, I'm chasing a 78 bottom end for a project and It would have to be sent to Boston...? Where are you...? How far from Boston...? Doesn't matter if you aren't interested, just asking, I have plenty of time to sort something out ...

Icefire · « **Reply #20 on:** February 23, 2015, 07:56:32 AM »

PM sent

cb650 · « **Reply #21 on:** February 23, 2015, 09:38:02 AM »

FYI the 79/80 have the same head/spacing. The 79 is way diff in everything except the engine.

Icefire · « **Reply #22 on:** February 24, 2015, 05:12:36 PM »

Picked up the 79 parts bike yesterday and got it home after a short 3 hr drive.
Removed the head cover today and checked out the cam and rockers that all look to be in good condition.

rb550four · « **Reply #23 on:** February 24, 2015, 06:04:38 PM »

The head looks better but what do you think caused that damage in pic #3 on the tappet? Any chunks laying around that head, maybe hiding out in the springs? And no damage to the cam, that's great
I'd be checking the oil passages closely while cleaning just to be sure bits aren't lodged in them.
Have you had a look see at the bottom end yet?
It looks like it has potential so far.

Icefire · « **Reply #24 on:** February 25, 2015, 08:08:20 AM »

Just taking a close look there are no signs of an debris in or around the springs but I will be taking the valves out to clean the head up. The plan is to lap the valves and replace the valve seals at which time I will check to insure the oil passages are clear.
I haven't looked at the bottom end yet as the motor is seized and am trying to loosen up the Pistons. When I removed the head there was a lot of build up on # 2 piston and # 4 had a 1/4" of WD sitting in it. The PO must have tried to loosen the motor up with no success.
There are some indents on the top of Pistons #2 and # 3 that are new. My guess is the PO put in the wrong plugs ( longer ) and the Pistons hit the electroids as the marks line up with where the plugs are located.

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Author Topic: Icefire's 79 CB650 Project (Read 5911 times)