Author Topic: First CB750 (Read 3189 times)

Rangle · « **on:** August 03, 2014, 05:38:52 PM »

Hey guys

Just recently purchased my first CB750 and am running into an issue I'm hoping I could get some help with. It's a 72 that the PO had recently had the top end rebuilt on. It seems to be leaking oil from the head gasket. After riding for about 45 minutes my boots and the lower part of my pants were covered in oil, more so on the right side. Once I got off the bike it sounded like air was pushing through some where on the motor and I saw little bubbles of oil coming from the left side head gasket. I'll get some pictures up to give a better idea of the area.

Rangle · « **Reply #1 on:** August 03, 2014, 05:41:57 PM »

Right where the head gasket sits and about 3/4ths of the way back is where I saw the leak.

calj737 · « **Reply #2 on:** August 03, 2014, 05:43:55 PM »

Here's the best thread for how to resolve this permanently and properly. The PO did not follow this process undoubtedly.

http://forums.sohc4.net/index.php?topic=107040.0

Rangle · « **Reply #3 on:** August 03, 2014, 05:44:59 PM »

Here you can see where the oil is dripping off of the fins after the ride.

madmtnmotors · « **Reply #4 on:** August 03, 2014, 05:46:36 PM »

When you tear it down for repair, check for this condition while you're at it:

http://forums.sohc4.net/index.php?topic=139737.msg1582480#msg1582480

I'm seeing more and more reports of this issue, on more forums than just this one. After five miles there was so much hot oil on my shin that I could feel the heat through my jeans.

Everybody's a mechanic...

+1 on the link in calj's post above.

Rangle · « **Reply #5 on:** August 03, 2014, 06:02:26 PM »

Awesome. Thanks for the advice guys. I'll keep you updated on how the engine removal and break down goes. First time doing any of this.

Rangle · « **Reply #6 on:** August 04, 2014, 08:59:05 AM »

Hey does this kit come with all the gaskets I would need to fix this leak? It looks like it to me but I would appreciate a second opinion. Also is there seller that is used more commonly? I saw Cycle X come up a few times.

http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-engine-parts-honda-cb750-engine-gasket-set-16-6118.html

bjbuchanan · « **Reply #7 on:** August 04, 2014, 07:05:15 PM »

Cycle x is nice when they have there 'better' gasket set in stock. My problem with DCC (with their set) they have NO BRAND NAME. Is it cheap 50$ ebay repackaged and marked up or something better? Something better is unlikely in my opinion due to the fact that 'better' is usually Honda (and a vendor brags about it) and sells for much more.

That being said, I used NE brand off of ebay for 50$. I used copper spray misted lightly in 2 coats on the head gasket, permatex non hardening sealant on the rubber pucks and mix/matched o-rings from Harbor Freight that fit certain locations better.

My torque value is of 18.5 ft lb is pushing it and I really snuck up on the value working up from 17.5. I let it rest for a day and then reapplied the torque wrench. Absolutely no leaks on my engine from the base gasket up. When I had done the low 14.5 value for torque it leaked immediately at start up. HUGE disappoint to say the least

With good techniques and proper assembly you can do this on the cheap. Cheap doesn't mean junk, you don't NEED an MLS Head Gasket, kibblewhite studs and viton o-rings for everything. Have a clean engine, proper non hardening sealant, correctly sized o-rings and the right torque values and you will be real happy

Rangle · « **Reply #8 on:** August 05, 2014, 06:21:07 AM »

My only concern would be my lack of experience with the engine. I've been doing quite a bit of research for this project and it seems like you need specific sized Gaskets as well as O rings. I don't think I would be able to mix and match parts. I do have the Haynes manual and just ordered My CB750 book which i think would help out. BJ were you able to do it with mix and matched parts because you have done it before and know your way around the bike, or am i making this harder than it actually is?

Thanks for the advice, I'd definitely like to be able to do it the same way you did.

cafesnrods · « **Reply #9 on:** August 06, 2014, 03:18:50 PM »

I have found some good stuff here:

http://4into1.com/

Rangle · « **Reply #10 on:** August 06, 2014, 05:44:47 PM »

Thanks, I'll definitely look into the link. It's it recommended to to get the oil seal kit with the the gasket set? I'm looking into the cycle x cb750 set, ENG-023. It doesn't specify years or come with a seal kit. Yay or Nay?

Rangle · « **Reply #11 on:** September 05, 2014, 11:30:15 AM »

Alright, so I recently pulled the engine out and stripped it down to the cylinders. I'm planning on building it back up this weekend. I've got a few pictures I'll post so if anyone sees anything I might need to replace or give some tlc i'd really appreciate it if you would point it out. Also any advice you've got is very welcome!

MCRider · « **Reply #12 on:** September 05, 2014, 11:47:47 AM »

I haven't read the full thread, my comments are from scanning. My first hand experience is I've built dry motors and leakers. Leakers are frustrating.

Yours is a 72 (K1 or K2), find out which. Parts are bought by VIN not by title year. Assuming your head, cylinder and cam cover is original. Easy to make it harder than necessary.

I've had the cam stud leaking issue and have commented on it a lot. IF your cam tower studs have never been disturbed, don't be tempted and disturb them.

A staggered approach to tightening head nuts is recommended by experienced builders. Takes forever. Some even say to tighten them down, sit overnight, loosen and do again.

My CycleX experience has been the best. They understand about proper ORings etc.

SOHC4 Cafe Racer Fan · « **Reply #13 on:** September 05, 2014, 12:27:11 PM »

All great advice. I've dealt with pesky leak issues and it's been a pain in the butt. Hence, I installed the Gordon's frame kit!

Rangle · « **Reply #14 on:** September 15, 2014, 10:05:31 AM »

Well with all the great advice from you guys I was able to actually rebuild the engine and stop the leaking. That victory was pretty short lived though. I'm sure it was a result of me being a new rider and also being new to older bikes but my chain snapped and punched a hole through my case about an hour after I got her back on the road. I'll post a pic. I'm imaging riding with this could cause a lot more damage so it looks like she'll be down for winter. Let me know what you guys think.

strynboen · « **Reply #15 on:** September 15, 2014, 10:15:46 AM »

if you can lokate the missing part..and vash/klean all up..just glue a small aluminium plate on the broken place..use sicaflex as glue..then test the gear work proper..if all runs..the last part of the seson are safe..later gett tig veldet the parts...or find a old engine and fix up..and have the bike running at same time...

70CB750 · « **Reply #16 on:** September 15, 2014, 10:32:13 AM »

Well, glad you kept the rubber side down.

As strynboen says, it can be glued as temporary fix and welded as permanent fix.

Rangle · « **Reply #17 on:** September 15, 2014, 11:27:02 AM »

I lost the missing pieces because this happened on a fairly busy road. Any thing I can do with missing parts?

vfourfreak · « **Reply #18 on:** September 15, 2014, 01:48:29 PM »

The missing piece may be inside your crank case.

Kev

oldhatt45 · « **Reply #19 on:** September 15, 2014, 01:50:11 PM »

Rangle,

I came across this thread the other day.

http://forums.sohc4.net/index.php?topic=133034.0

I was looking for something else, but thought this thread was interesting.
It may help you out in doing the repair.

Charlie

SOHC4 Cafe Racer Fan · « **Reply #20 on:** September 15, 2014, 08:11:02 PM »

Quote from: Rangle on September 15, 2014, 10:05:31 AM

Well with all the great advice from you guys I was able to actually rebuild the engine and stop the leaking. That victory was pretty short lived though. I'm sure it was a result of me being a new rider and also being new to older bikes but my chain snapped and punched a hole through my case about an hour after I got her back on the road. I'll post a pic. I'm imaging riding with this could cause a lot more damage so it looks like she'll be down for winter. Let me know what you guys think.

I'm not sure I would attribute snapping and throwing a chain to an inexperienced rider. Was it an old chain. If so, I might attributed it to not replacing a worn stretched chain. It truly sucks, but it is repairable.

MCRider · « **Reply #21 on:** September 15, 2014, 10:00:57 PM »

Quote from: CB750 Cafe Racer Fan on September 15, 2014, 08:11:02 PM

Quote from: Rangle on September 15, 2014, 10:05:31 AM
Well with all the great advice from you guys I was able to actually rebuild the engine and stop the leaking. That victory was pretty short lived though. I'm sure it was a result of me being a new rider and also being new to older bikes but my chain snapped and punched a hole through my case about an hour after I got her back on the road. I'll post a pic. I'm imaging riding with this could cause a lot more damage so it looks like she'll be down for winter. Let me know what you guys think.

I'm not sure I would attribute snapping and throwing a chain to an inexperienced rider. Was it an old chain. If so, I might attributed it to not replacing a worn stretched chain. It truly sucks, but it is repairable.

That's right. More likely, it was either an old tired chain to begin with, and/or, it had battery acid drip on it, doesn't take much, just vapors will do it. Pay attention to where the battery drain tube exits. See this Honda Service bulletin.
http://forums.sohc4.net/index.php?topic=102388.0
I run my tube to the right side of the bike, tie wrapped to the centerstand bracket, as far from the chain as possible.

Good reason to use a gel battery.

SOHC4 Cafe Racer Fan · « **Reply #22 on:** September 15, 2014, 10:30:54 PM »

Quote from: MCRider on September 15, 2014, 10:00:57 PM

Quote from: CB750 Cafe Racer Fan on September 15, 2014, 08:11:02 PM
Quote from: Rangle on September 15, 2014, 10:05:31 AM
Well with all the great advice from you guys I was able to actually rebuild the engine and stop the leaking. That victory was pretty short lived though. I'm sure it was a result of me being a new rider and also being new to older bikes but my chain snapped and punched a hole through my case about an hour after I got her back on the road. I'll post a pic. I'm imaging riding with this could cause a lot more damage so it looks like she'll be down for winter. Let me know what you guys think.

I'm not sure I would attribute snapping and throwing a chain to an inexperienced rider. Was it an old chain. If so, I might attributed it to not replacing a worn stretched chain. It truly sucks, but it is repairable.
That's right. More likely, it was either an old tired chain to begin with, and/or, it had battery acid drip on it, doesn't take much, just vapors will do it. Pay attention to where the battery drain tube exits. See this Honda Service bulletin.
http://forums.sohc4.net/index.php?topic=102388.0
I run my tube to the right side of the bike, tie wrapped to the centerstand bracket, as far from the chain as possible.

Good reason to use a gel battery.

I'm a big fan of gel and lithium ion batteries. The lithium ion batteries are not only service-free, but are MUCH lighter and have more cranking power.

Green1 · « **Reply #23 on:** September 16, 2014, 01:54:37 AM »

I put motobatt batteries in all my bikes no chance of them leaking.The one in my Trophy 1200 is even mounted on its side
Why risk broken chains or acid stains.

Rangle · « **Reply #24 on:** September 16, 2014, 05:05:17 AM »

So do you think I'll need to strip the engine back down to search for broken pieces in the crank case? Also it seems like aluminum and jb weld work as a quick fix for this. It's this something you guys would do or should I just start searching for a new case?

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Author Topic: First CB750 (Read 3189 times)