Author Topic: Cracked engine case (Read 4377 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.

calj737 · « **Reply #18 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.

Whyamihere · « **Reply #19 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 #20 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 #21 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 #22 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 #23 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

calj737 · « **Reply #24 on:** January 19, 2017, 03:28:58 am »

Since it's a Sandcast, it needs to be repaired, and professionally. I didn't realize when I wrote what I did that it was a Sandacast. Welding those cases is a great deal trickier. The cases are more porous than the later die cast ones, and as such, will bubble out impurities while being welded. It will require tremendous patience to control the heat and duration of it to avoid pockets of spooge erupting on you.

As for repairing chain damage ahead of the sprocket, I would not undertake that wituothout a compete teardown of the engine, heavy degreasing, perhaps a bit of grinding the edges, and welding with copper back shields. Plus, forming a piece of aluminum to match the profile to be seam welded in will take some time and skill.

Defintely worth saving, but definitely needs professional workmanship to come out right and be stable afterwards.

News:

Author Topic: Cracked engine case (Read 4377 times)