Author Topic: Cracked engine case (Read 4608 times)

Whyamihere · « **on:** January 16, 2017, 05:35:11 PM »

Hello everyone. I have a cb750 I acquired. The engine case is cracked. It looks like the chain broke and smashed the case. It looks like someone did a halfas% job repairing it. Any ideas on how if can be fixed properly .......diy job preferably if not can any machine shop fix it or do I have to go somewhere that specializes in engines. Thanks

Sent from my SM-T550 using Tapatalk

flybox1 · « **Reply #1 on:** January 18, 2017, 07:58:50 AM »

It may be cheaper just to get a set of used cases off feebay.
Depends on how bad the hole is.
Post up a picture.

lrutt · « **Reply #2 on:** January 18, 2017, 08:15:43 AM »

Pics could help. Honestly a good JB weld patch could last you a lifetime.

innovativems · « **Reply #3 on:** January 18, 2017, 08:47:24 AM »

A very good welder can repair the area. Just make sure they really know what they are doing. Did this on the same situation on a cbr1000rr that someone used a clip style master on

Sent from my iPhone using Tapatalk

grcamna2 · « **Reply #4 on:** January 18, 2017, 09:57:45 AM »

Quote from: flybox1 on January 18, 2017, 07:58:50 AM

It may be cheaper just to get a set of used cases off feebay.
Depends on how bad the hole is.
Post up a picture.

pics..

754 · « **Reply #5 on:** January 18, 2017, 10:00:41 AM »

Tell us the year the later, the cheaoer the cases..except 77/78. We need more info and a pic.

Don R · « **Reply #6 on:** January 18, 2017, 10:04:57 AM »

There may be damage inside that you can't see, it kinda depends on the size and depth of the hole. I had one that was so far in, the chain fell out the bottom of the engine.

flybox1 · « **Reply #7 on:** January 18, 2017, 10:09:53 AM »

Quote from: Don R on January 18, 2017, 10:04:57 AM

There may be damage inside that you can't see, it kinda depends on the size and depth of the hole. I had one that was so far in, the chain fell out the bottom of the engine.

OH, the Horror!

major domo · « **Reply #8 on:** January 18, 2017, 10:21:57 AM »

My brother had this happen to his '71 750 years ago-chain right thru the case due to an ill-fitting custom chain guard, which snagged the chain. If you try to repair those cases, you must be very carefull to completly flush out the oil galleries to remove any metal swarf caused by the fracturing of the cases, as any left behind may cause a blockage and subsequent oil starvation and damage to the engine. My brother learned the hard way in not completly dis-mantling the engine to do said flushing, and had a partial seizure due to aluminum swarf left behind in the oil galleries. Result? He had to dismantle/repair the engine again. Such a shame, as it was a beautiful gold '71 750. He sold it shortly after the second rebuild.

chewbacca5000 · « **Reply #9 on:** January 18, 2017, 12:15:32 PM »

Quote from: innovativems on January 18, 2017, 08:47:24 AM

A very good welder can repair the area. Just make sure they really know what they are doing. Did this on the same situation on a cbr1000rr that someone used a clip style master on

Sent from my iPhone using Tapatalk

I came across a k1 engine that was welded and slathered with JB weld. I wish I knew is was welded before I tried to separate the cases.

Stev-o · « **Reply #10 on:** January 18, 2017, 03:37:41 PM »

grcamna2 · « **Reply #11 on:** January 18, 2017, 03:44:29 PM »

Ahhh,now that's more like it

!

Whyamihere · « **Reply #12 on:** January 18, 2017, 04:37:06 PM »

Sent from my SM-G900V using Tapatalk

Whyamihere · « **Reply #13 on:** January 18, 2017, 04:38:00 PM »

By the way, that that pic made day Stev-o

Sent from my SM-G900V using Tapatalk

Whyamihere · « **Reply #14 on:** January 18, 2017, 04:39:08 PM »

That's all I can find on my phone right now. I have to take better ones.

Sent from my SM-G900V using Tapatalk

Whyamihere · « **Reply #15 on:** January 18, 2017, 04:45:04 PM »

With a number like that I'm not trying to get a new case.

Sent from my SM-G900V using Tapatalk

Stev-o · « **Reply #16 on:** January 18, 2017, 04:54:29 PM »

Quote from: Whyamihere on January 18, 2017, 04:38:00 PM

By the way, that that pic made day Stev-o

Glad to be of service!

BomberMann650 · « **Reply #17 on:** January 18, 2017, 05:16:57 PM »

What attaches there?

If you have the missing piece you could have it welded back on.

Whyamihere · « **Reply #18 on:** January 18, 2017, 06:23:11 PM »

Quote from: calj737 on January 18, 2017, 06:20:45 PM

Thats the shift cover on the left side (if I'm not mistaken). Easy enough to fill that hole with all new weld. Then, drill it, and tap it.

If you undertake that, I'd drill the threads out first with a slightly larger bit. This will help clean the hole a little bit before welding. Hit the cracked area with Propane to help purge the impurities. Brush aggressively with stainless steel brush, wipe with acetone, and weld it fully solid.

Let cool, drill, tap, replace cover and ride on! 2 Hours or so of work.

Thank you for the info.

Sent from my SM-G900V using Tapatalk

ekpent · « **Reply #19 on:** January 18, 2017, 06:23:54 PM »

Its a screw hole broken for the sprocket cover. Actually the other screw lower would still hold it on just not look good. Is there any other visible damage in the area especially where the cases meet down lower inside. May need to be cleaned to see well.

PS-You kind of hit the JACKPOT because your engine is a SANDCAST !!!

What is the frame number ? The engine is a 1969.

754 · « **Reply #20 on:** January 18, 2017, 11:39:22 PM »

I would trade a good set of cases for those..
Is it leaking /broken in front of the spocket ? Or just that theaded part .?
Those should be fixed.. Do you have the rest of the bike ?

Whyamihere · « **Reply #21 on:** January 19, 2017, 03:18:47 AM »

There is more damage in front of the sprocket, no leaking though. Frame is a sandcast also #5647.

Sent from my SM-G900V using Tapatalk

PeWe · « **Reply #22 on:** January 19, 2017, 03:24:59 AM »

Important to repair it properly by an alu welder. A sandcast should not get any temporar repair with 2k glue.
Restore the bike properly and it will help your retirement

Whyamihere · « **Reply #23 on:** January 19, 2017, 03:32:08 AM »

I appreciate all the feedback, thanks.

Sent from my SM-G900V using Tapatalk

gschuld · « **Reply #24 on:** January 19, 2017, 03:18:21 PM »

I couldn't tell you for certain how much different it is welding on sandcast engine cases to the later die cast cases, but I have had a successful repair done to a k1 diecast upper case that was severely damaged in battle. It would NOT have been worth the effort if this particular case did not come from a former world record breaking dragbike.

The best I know is Jim French, here on the forums. He owns and has mastered welding equipment that is basically "NASA" level stuff. He has done several repairs for me. Simply outstanding work....

I'd bet if you asked your most skilled welder locally about laser welding perfectly uniform 1/16" wide dimes under a microscope like Jim can, they would ask what you were smoking.

If I had a broken sandcast case, he would be my first call. For sure.

George

754 · « **Reply #25 on:** January 19, 2017, 04:25:38 PM »

Can you fill us i. On the story of the bike..where you found it,
What it looked like.. The deal..did it take months or years, or barnfind , craigs..etc...
I found an earlier one than that in a barn and it was 85percent complete..

Whyamihere · « **Reply #26 on:** January 19, 2017, 05:15:42 PM »

Quote from: 754 on January 19, 2017, 04:25:38 PM

Can you fill us i. On the story of the bike..where you found it,
What it looked like.. The deal..did it take months or years, or barnfind , craigs..etc...
I found an earlier one than that in a barn and it was 85percent complete..

My grandmother's tenant passed away and his family did not want any of his things. He was hard core into cb750s, he had built easy 20 of them, I ended up with what ever parts were in his apartment when I cleaned it out.

Sent from my SM-G900V using Tapatalk

Whyamihere · « **Reply #27 on:** January 19, 2017, 05:16:54 PM »

This was in the living room.

Sent from my SM-G900V using Tapatalk

gschuld · « **Reply #28 on:** January 19, 2017, 05:34:59 PM »

Well, you are a very lucky fellow indeed. Sandcasts are very rare and equally expensive to restore to a condition that they deserve if you were so inclined. I am into diecast K0s myself, that's as rare as I can justify playing with.

I wish you the best of luck with it.

George

754 · « **Reply #29 on:** January 19, 2017, 05:47:44 PM »

That has to be one of the coolest sandcast stories..
How old was the guy ?
Any spare stuff... Anything you need help to identify?

Stev-o · « **Reply #30 on:** January 19, 2017, 06:00:08 PM »

Yes, great story. Lucky you!

Whyamihere · « **Reply #31 on:** January 19, 2017, 06:03:19 PM »

He was a cool dude, he was my neighbor for about 6 years, I was into new sport bikes and he was into the cb's. He about 60.

Sent from my SM-G900V using Tapatalk

gschuld · « **Reply #32 on:** January 19, 2017, 06:14:31 PM »

Very cool.

I sent you a PM.

George

News:

Author Topic: Cracked engine case (Read 4608 times)