Author Topic: Another barn find...76 CB750F (Read 3733 times)

tommytwotone · « **on:** July 17, 2011, 06:28:19 PM »

I never thought I would have one of those great barn find stories but here it is. After building my 72 CB500 one of my best friends looked at it and said "hey I have one of these in my barn,do you want it"? Naturally I said yes thinking it would be a great project for my son and I to work on. So we decided to create a build thread and let you guys help us out.

We went to pick it up yesterday, and discovered it was a CB750 Super Sport, and took a picture of it outside of the barn it has been stored in for 22 years. Yea that's right it hasn't been on the road since 1980. The bike is not overly rusted but the motor won't turn over. Got it on the trailer and home with only one incident. The damn thing fell on me as I was pushing it up on the trailer. No one was hurt but now I'm determined to make this thing run and look like new. Not sure how long it will take us but I hope to have it done by the end of the year.

Here it is out side of it's old resting place.

The second pic is after we removed a few parts trying to see what all needed to be done.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #1 on:** July 17, 2011, 07:13:49 PM »

Nice find! It could be 76 with different body work but Candy Sapphire Blue was 1975 which were made from 1/75 until early 4/75.

tommytwotone · « **Reply #2 on:** July 17, 2011, 08:57:56 PM »

Thanks I will investigate before I start the rebuild. My main concern is getting the motor to turn over. Soaking it in Marvel Mystery Oil to see if I can get it to move.

BeSeeingYou · « **Reply #3 on:** July 17, 2011, 10:37:27 PM »

Been a lot of 750F's popping up out of the sheds lately. Nice find and she looks like a solid basis for your project.

Cevan · « **Reply #4 on:** July 18, 2011, 07:23:46 AM »

I look forward to your restoration. I just picked up a CB750F1 yesterday.

tommytwotone · « **Reply #5 on:** July 19, 2011, 05:53:07 AM »

Okay I was able to get the motor to turn over using a strap wrench on the stator. No luck with the kick start. It feels like the kick start is stuck. Is there any way to get the kick start apart with out tearing down the engine? or should I get the motor turning more freely before I can expect the kick to be able to turn the motor? The electric starter won't turn it either but it turns rather easily with a wrench on the crank. Also when I am turning with the wrench I can see the transmission shaft turning so I don't think the trans is locked up. It is in neutral so everything should be free to turn. Still soaking it in oil. maybe after a few more days it will free up. Any ideas how to free it up quicker?

Tom

BeSeeingYou · « **Reply #6 on:** July 19, 2011, 06:13:51 PM »

Does the electric start even sound like it's engaging. The starter button is a common failure point so could that be the issue?

Tews19 · « **Reply #7 on:** July 19, 2011, 06:44:24 PM »

Nice find. I have been driving the back roads looking at possible places to find another barn find... I will follow this thread.. Nice find once again

tommytwotone · « **Reply #8 on:** July 19, 2011, 06:52:54 PM »

Starter does engage just won't turn the motor over. The starter button is no good so I have to short across the solenoid. Still turning it by hand trying to get it to free up a bit more. Hopefully a few days soaking will help free it up.

Tom

MCRider · « **Reply #9 on:** July 19, 2011, 07:33:56 PM »

Nice find!

Ther are much more powerful penetrants than Mystery Oil, not the least of which is 50/50 Acetone/ATF.

You'll want to change your oil post haste if you get it to spin or, heavens, start.

tommytwotone · « **Reply #10 on:** July 20, 2011, 07:09:25 AM »

Thanks. I don't plan to start it until I am sure that there is nothing else wrong. Ive drained the oil and cleaned what I can without tearing the motor apart. I think I will probably tear it down once I get it to turn over. What are the chances of getting it to run reliably after getting it to turn and or start? The crank case was full of oil but I am assuming that there was rust and corrosion on the cylinder walls and that is what has kept me from getting it to turn.

If I keep flushing the cylinders with penetrating oil and do what I can to flush the crank case can I get away with running it with out a complete tear down?

Tom

BeSeeingYou · « **Reply #11 on:** July 20, 2011, 09:25:51 AM »

Quote from: tommytwotone on July 20, 2011, 07:09:25 AM

Thanks. I don't plan to start it until I am sure that there is nothing else wrong. Ive drained the oil and cleaned what I can without tearing the motor apart. I think I will probably tear it down once I get it to turn over. What are the chances of getting it to run reliably after getting it to turn and or start? The crank case was full of oil but I am assuming that there was rust and corrosion on the cylinder walls and that is what has kept me from getting it to turn.

If I keep flushing the cylinders with penetrating oil and do what I can to flush the crank case can I get away with running it with out a complete tear down?

Tom

There is a good chance that it will run fine. I would get it running and then decide. SeaFoam does wonders for stuck rings and just running it may reseat them. It may smoke a bit for a day or two. While my 76F did not have a stuck motor it sat for 25 years without being run and it has no problems and burns no oil.

tommytwotone · « **Reply #12 on:** July 25, 2011, 08:06:53 PM »

Well it seems that something is bad broke. Can't get the motor free enough to be able to turn it over with the kick or the starter. So we have decided to tear it down and see what's on the inside. Got the motor out of the frame and will post pics of the tear down as soon as we start.

noahspop · « **Reply #13 on:** July 26, 2011, 08:26:31 AM »

I'm all aboard. I want to see whats wrong with the bike and of course the out come of the bike . Congrats on the fine.

tommytwotone · « **Reply #14 on:** August 01, 2011, 12:56:56 PM »

Well I finally got the motor apart after much huffing and puffing. Three of the cylinders were really stuck. The rings have become one with the pistons. Still working on getting them apart. The cylinders look pretty good though. I think i will get them honed and replace the rings as well as all of the gaskets and seals. The rest of the motor looks good except for the hole in the case where the chain chewed on it. I think i can get that welded and be good as new.

Tews19 · « **Reply #15 on:** August 01, 2011, 01:04:18 PM »

NIce job getting it apart.. Can you take pics of the rings that have become part of the pistons? I have never seen that and am very curious to see what that looks like.

tommytwotone · « **Reply #16 on:** August 01, 2011, 01:05:27 PM »

Took me minute but there you go.

Tews19 · « **Reply #17 on:** August 01, 2011, 01:24:16 PM »

Ohhhh man. You boring up to 836?

tommytwotone · « **Reply #18 on:** August 01, 2011, 01:30:48 PM »

no just leaving it standard.

tommytwotone · « **Reply #19 on:** August 07, 2011, 08:21:41 PM »

Well I got a little further today. The bike is completely stripped and the frame is sandblasted and primed.

Sending the chrome to Mexico to be re-chromed. The motor is all cleaned up and waiting for parts.

Had a little problem getting the rings off of the pistons. I'm going to have to replace one of the pistons because I broke the ring grove trying to remove the ring. I have never seen pistons stuck quite as bad as those before.

So now the fun begins of cleaning the stack of parts and putting them back together. Here is a few pictures of the progress.

Tews19 · « **Reply #20 on:** August 08, 2011, 05:18:18 AM »

That looks fun... I need to improve my tool collection to allow me to do builds.

fatkid · « **Reply #21 on:** August 08, 2011, 10:45:47 AM »

love the project . I to just dug out a 76f and got it back on the road . great bike . how many miles were on it? good luck and keep us posted.

MRieck · « **Reply #22 on:** August 08, 2011, 02:36:59 PM »

Did you check the top end? I assume you replaced the vale guide seals.

News:

Author Topic: Another barn find...76 CB750F (Read 3733 times)