Topic: Weeping between the fins

[kaysystems]

Whereas the old studs in good condition can only be torqued to say 18 ft lbs (I know the book says less, but I always did and got away with it) the RC studs are good for 24+ ft lbs.

Thanks

And I always thought it was the threads in the crankcase that determined the torque. I thought they would pull out.

David

[Raul CB750K1]

Thanks

And I always thought it was the threads in the crankcase that determined the torque. I thought they would pull out.

David

That makes sense. I recognize Terry's expertise, but for my inexperienced point of view seems that the weakest link in the chain would be the alloy crankcase threads more than the studs...

[Jerry Rxman Griffin aka MuthaF'er]

Whereas the old studs in good condition can only be torqued to say 18 ft lbs (I know the book says less, but I always did and got away with it) the RC studs are good for 24+ ft lbs.

Thanks

And I always thought it was the threads in the crankcase that determined the torque. I thought they would pull out.

David

Yes and no. Yes threads can let go. However the main issue with weeping is that with time, miles, and twisting throttle (abuse/use) the stock diameter cylinder studs will stretch slightly thereby loosening the grip between the cylinders and the head. If you compare the APE studs with stock studs you will see the threads are the same diameter but the APE shaft is larger. The shaft will take higher torque without the stretch. Now, how much torque does it take to strip the threads I do not know therefore I will follow their recommendation when installing their studs.  I do know that you really need a stud removal socket tool to get studs out in order to prevent any damage!

[Raul CB750K1]

I give you that standard studs can stretch (my bike is 35 years old). With such reasoning, if I retorque the head I would be good to go, isn't it?

[Jerry Rxman Griffin aka MuthaF'er]

Raul,

Short of taking off the top end and replacing the studs (which I would/will do for $90 US if it were apart), that's about the best option I see. It would be interesting to see what the torque readings are before tightening just to see how much difference there might be. I'm sure we can get some responses from guys that have done this and see how many miles they got before it started leaking again if this actually stopped the leak. The thing is 99% of us have to pull the motor even to torque all the nuts and in the proper sequence. If we go to this much trouble why not do it right (other than cash)?     

[kaysystems]

Since my K0 is apart right now because the head gasket was leaking in the centre, I will buy the super-studs and tighten it nicely.

David

[TwoTired]

All bolts/studs will stretch.  But, there is a difference between elastic stretch and stretch to yeild.  Some studs/bolts are designed to torque to yeild.  These actually are deformed during installation and can't be reused because another stretch to yield will weaken them.  The metal becomes work hardened and brittle, prone to breakage.  If you overtorque a stud, it can be the difference between stretch within its elasticity limits and stretch to deformity, at which point the stud is essentialy ruined.  I believe putting a fatter, stronger stud it its place will certainly put more stress on the case AND the threads, particularly if it is overtorqued.  Seems like there would be some extra case distortion with overtorque, too.

I've not seen any metalurgic specifications for the SOHC4 studs or the case threads.  I've also not tested the case/threads or the studs for torque failure limits.  I just rather assumed Honda didn't lie about what is best for their engine.

Vibration and shock do tend to relax steel in tension over time.  I can imagine a stud in service tension and vibration for 30 years can lose its original torque setting.  Not sure how to calculate the magnitude, though.

Cheers,

[Terry in Australia]

I have no technical qualifications to question the metallurgy of OEM Honda cases or studs, nor can I waffle on about how old Mr Honda perfected the motor-bicycle in 1969 without my nose growing exponentially, so instead, I'll just resort to common sense.

The studs that I removed from my 35 year old engine looked remarkably good apart from 2 short studs that were quite badly corroded, but once again, anyone here who actually knows anything about CB750's knows that oil leaks around the head gasket area can usually be attrributed to the OEM studs stretching, so if you're already faced with the prospect of removing your engine and (at least) replacing your head gasket, "O" rings, rubber pucks under the cam towers, cam cover gasket etc etc, then shoving that 200+ pound lump of finger crunching metal back into the frame while chanting the "Lords Prayer" over and over in an effort to ward off demonic oil leaks, (because once you've pulled a 750 engine out of a frame, you NEVER want to do that again) why wouldn't you replace those ancient spindly studs while you're at it?     

Blind faith is no doubt a wonderful thing to possess, but considering that race bike builders have been replacing the OEM Honda studs with APE or RC items for as long as Honda has been making them, I'm happy to be branded an "Un-believer" if all my oil stays inside my engine and off my disco pants and buckled shoes, ha ha! Cheers, "Heretic" Terry.  

[ofreen]

I have a '75 750F.  In 1996 at 52,000 miles, the engine began weeping badly at both the head and base gaskets.  It got bad enough at the head gasket that my Levis would get oiled pretty good after a 10 mile ride.  I pulled the engine out and retorqued the head.  Usually when I retorque a head, I'll back off the nut or bolt about 1/4 of a turn, then retighten.  With the 750, when I'd loosen a nut, rather than coming loose gradually, it would 'pop', then be very loose.  After retorquing, all weeping at both the head and base gaskets stopped.

In 2002, at 82,000 miles, I had to replace the seals under the cam towers.  While the engine was out, I took the opportunity to retorque the head again, even though there were no leaks at the head.  The bike is now at 104,900 miles and there are no leaks.

[TomC]

Hi group
     Re-torquing of head studs or bolts is standard maintenance on many engines. It is unfortunate that Honda did not engineer the 750 so that could be done with out removing the engine.
          TomC

[SohcCBs]

I have a '75 750F.  In 1996 at 52,000 miles, the engine began weeping badly at both the head and base gaskets.  It got bad enough at the head gasket that my Levis would get oiled pretty good after a 10 mile ride.  I pulled the engine out and retorqued the head.  Usually when I retorque a head, I'll back off the nut or bolt about 1/4 of a turn, then retighten.  With the 750, when I'd loosen a nut, rather than coming loose gradually, it would 'pop', then be very loose.  After retorquing, all weeping at both the head and base gaskets stopped.

In 2002, at 82,000 miles, I had to replace the seals under the cam towers.  While the engine was out, I took the opportunity to retorque the head again, even though there were no leaks at the head.  The bike is now at 104,900 miles and there are no leaks.

I may try this first, but I'll be making a kit to cut and replace the trianglular supports at the top.  I found a guy a couple years back that had just cut his out and didn't replace them at all.....and has been riding it for about 4 years since.  I will though, replace the triangular framing support......and of course I'll photograph or video the procedure and report the results over time.

[seaweb11]

There was a very detailed thread on this topic of frame cutting here not to long ago

[TwoTired]

Hey Terry!
 Your post was way more wordy than mine.  Did you find an extra reserve of wind pent up inside?  ha ha!

By the way, I really don't mind if you want to copy what other people have done to their machines.  You might even make it better!  And lord knows, those other guys have to eat, too. ha Ha!

Cheers,

[Terry in Australia]

Hey Terry!
 Your post was way more wordy than mine.  Did you find an extra reserve of wind pent up inside?  ha ha!

By the way, I really don't mind if you want to copy what other people have done to their machines.  You might even make it better!  And lord knows, those other guys have to eat, too. ha Ha!

Cheers,

G'Day TT, where have you been hiding mate? Ha ha, you're right though, I was at work so had plenty of time to waffle on about "stud theory", I really should start earning my pay, but our contract is due to expire soon, so I guess I'll just have to save all that energy, for the new contract, ha ha! Cheers, Terry.

[kaysystems]

I suspect that Honda calculated the force they believed necessary to clamp everything together. From there they calculated a torque for the studs. Unfortunately the gaskets, compress, the studs stretch and the metal used in the cases & head would settle. The result is less clamping force to hold the head on.
I have no problem therefore with starting out with a higher torque and when everything settles I hope that I have enough force.

Anyone know what the torque for a DOHC CB750 is or a Kawasaki Z900 head would be, for comparison?

David

[Bob Wessner]

Blind faith is no doubt a wonderful thing to possess, 

Terry,

Did you just slip a Bushism in on us? 

[mick750F]

Blind faith is no doubt a wonderful thing to possess, 

Terry,

Did you just slip a Bushism in on us? 

   I'd like to hear more about his "stud theory". 

Mike

[SohcCBs]

There was a very detailed thread on this topic of frame cutting here not to long ago

Yes, I've seen info on this from time to time over the years......I have been putting it off. 

[TwoTired]

G'Day TT, where have you been hiding mate?

Been trying to avoid the Government/Medical business colusion...unsuccessfully.  You know they can mutilate a healthy individual with no repercussions and get paid to do it...legally?

Wait the Gubmt does that with the military, too!  Come to think of it, they do that with everything! 

Pity I have too many scruples to join them.  Might have a survivor's chance then.

Be well!!  

[Terry in Australia]

Blind faith is no doubt a wonderful thing to possess, 

Terry,

Did you just slip a Bushism in on us? 

Good one Bob, well I guess there's a difference between "possessing" blind faith, and "being possessed by" blind faith, ha ha! Ok, I better stop making political statements, lest someone here strangles me with their flag! Cheers, Terry.  

[Terry in Australia]

Blind faith is no doubt a wonderful thing to possess, 

Terry,

Did you just slip a Bushism in on us? 

   I'd like to hear more about his "stud theory". 

Mike

You'll have to buy the book Mike........... (don't worry about missing out on a copy, I only got 12 published, and still have 11 left, boohoo!)

[Terry in Australia]

Yes, I've seen info on this from time to time over the years......I have been putting it off. 

I would really like to do this too, but I know it'll ruin the frame's integrity. After removing/installing my CB750 engine twice in the last 3 weeks, I never want to do that again, so I'm thinking about alternatives.

A the moment I'm dreaming about removing the frames bottom rails below the front and rear engine mounts, and using the engine as a stressed member of the frame. It's been done before by other frame builders, (Fritz Egli, for example)but this was in new "purpose designed" frames, not existing Honda frames, and once again without just "going for it", I don't have the technical expertise to calculate all the variables and come up with an answer before I fit a new blade to my hacksaw? Cheers, Terry.    

[SohcCBs]

I appreciate all the tech input from everyone!...but consider that when people use the search function to find technical info, sorting thru all the off topic fun makes finding the data they're looking for difficult.  I'm not trying to spoil anyones fun, but people really need the valuable data that SOHC4 and members provide.  That's why it's here.

Thanks!!

[SohcCBs]

Yes, I've seen info on this from time to time over the years......I have been putting it off. 

I would really like to do this too, but I know it'll ruin the frame's integrity. After removing/installing my CB750 engine twice in the last 3 weeks, I never want to do that again, so I'm thinking about alternatives.

A the moment I'm dreaming about removing the frames bottom rails below the front and rear engine mounts, and using the engine as a stressed member of the frame. It's been done before by other frame builders, (Fritz Egli, for example)but this was in new "purpose designed" frames, not existing Honda frames, and once again without just "going for it", I don't have the technical expertise to calculate all the variables and come up with an answer before I fit a new blade to my hacksaw? Cheers, Terry.    

I found a guy a year ago that had removed the triangular rails and just left them off.  He's been running it that way for years with no noticible effects.  He like me, probably isn't trying to race all over the place though.  My only concern is the torque my 836 and cam puts out, so that's why I'm going to put the rails back.

[Terry in Australia]

OK mate, well if you want to do it properly, get on to Gordon (Ilbikes here) he did a very professional job of removing the side support rails and modded them so that they could be bolted back in, if you just leave them out completely you're gambling with your life. Cheers, Terry.