Leaking head and base gaskets...can they be re-torqued?

GMX

GMX

Veteran Member
Joined
Dec 17, 2024
Total Posts
403
Total likes
480
Location
Arizona
CL450 K4 sat for many years ignored and unloved.
I rebuilt the carbs, adjusted the cam chain and valves and set the points and timing. Coils and condensor checked out aok.
She starts right up and runs strong, but after about 20 miles, it looks like oil is seeping at the head gasket and cylinder base.
I think this motor may have been rebuilt at some point as the mounting bolts were all facing the wrong way from the parts diagrams indicating it had been removed from the frame.
But who knows anything for certain on a 50+ year old bike?
I really don't want to rebuild the motor on this bike but would like to know from the more experienced guys here if the head bolts could be loosened and retorqued
to help slow or stop the oil leaks.
If so, what would be the correct step by step method?
 
Id say worth a try!
I loosen the headsteady prior to retorque but don't know if that makes a difference
 
I'm sure it could work in some situations and obviously it's worth a try, but all the times I've done it haven't stopped any top end leaks ever, and really didn't change any of them either. There's also the possibility that a cam chain left too loose for a long time has carved a thin spot in the cam chain tunnel somewhere that is now leaking from a pinhole in it somewhere.
 
Well, darn. OK
I may still give it a try.
The FSM Section 3.2 Cylinder Head Reassembly says the nuts should be loosened in reverse of the tightening sequence.
Torque is 21.7 ft-pounds as in the sequential diagram.
Should the crankshaft/valves be in any particular position when slightly loosening and then retorquing the head bolts?
 
GMX said:
Well, darn. OK
I may still give it a try.
The FSM Section 3.2 Cylinder Head Reassembly says the nuts should be loosened in reverse of the tightening sequence.
Torque is 21.7 ft-pounds as in the sequential diagram.
Should the crankshaft/valves be in any particular position when slightly loosening and then retorquing the head bolts?
Click to expand...
Not that I'm aware of, no.
 
The topic of retorquing a head has been and remains a little mysterious to me.
  • Sometimes it is mentioned that the head should be checked/retorqued after a freshly built motor is put through a full heat cycle or some small number of miles. I have checked the head when the nuts are exposed (CB350/CB450), but generally not when they are covered (CB360/CB750). Not sure what other people do, nor what is recommended.
  • I tried retorquing the head on my recent CB350 build to cure a leak. It didn't work because it wasn't a head leak! I rebuilt the top end twice before realizing that, so three sets of gaskets when I only needed one. I went beyond the torque listed in the FSM and I recall other members mentioning that they do that as a matter of course on their rebuilds. So, maybe you could consider increasing the torque slightly rather than retorquing the head.
  • The head gasket should only be used once because of the crush rings around the cylinders, so the nuts must be loosened and tightened individually. Otherwise there is a big risk that things will move and whatever seal was achieved could be compromised. If one accepts this idea, then it is natural to ask whether the torque sequence makes any difference for this operation. I'm not sure it does, but I think I would use the tightening sequence rather than the reverse sequence, especially if the torque is being increased.
We all know the correct way to address a bonafide head leak, but I will agree that there is little to lose by trying something like this as long as one does not go overboard with the torque wrench.
 
stl360+450 said:
The topic of retorquing a head has been and remains a little mysterious to me.
  • Sometimes it is mentioned that the head should be checked/retorqued after a freshly built motor is put through a full heat cycle or some small number of miles. I have checked the head when the nuts are exposed (CB350/CB450), but generally not when they are covered (CB360/CB750). Not sure what other people do, nor what is recommended.
  • I tried retorquing the head on my recent CB350 build to cure a leak. It didn't work because it wasn't a head leak! I rebuilt the top end twice before realizing that, so three sets of gaskets when I only needed one. I went beyond the torque listed in the FSM and I recall other members mentioning that they do that as a matter of course on their rebuilds. So, maybe you could consider increasing the torque slightly rather than retorquing the head.
  • The head gasket should only be used once because of the crush rings around the cylinders, so the nuts must be loosened and tightened individually. Otherwise there is a big risk that things will move and whatever seal was achieved could be compromised. If one accepts this idea, then it is natural to ask whether the torque sequence makes any difference for this operation. I'm not sure it does, but I think I would use the tightening sequence rather than the reverse sequence, especially if the torque is being increased.
We all know the correct way to address a bonafide head leak, but I will agree that there is little to lose by trying something like this as long as one does not go overboard with the torque wrench.
Click to expand...

Hmmm,
Your post does make sense to me, especially about the head gasket only being used one time, so not to loosen all the nuts at once.
I have not tried anything yet, but will try checking the torque (21.7 ft-lb) as per the FSM sequence one nut at a time and see if there is any movement. If not, I will go back and increase the torque slightly on each nut, again, one at a time in sequence and see if that makes any difference.
For that procedure should I loosen a nut first and then increase torque, or just see if I can increase torque without first loosening a nut one at a time?
Just not sure how much over I should attempt..any ideas on that?

PS if your leak was not a head leak, what was the problem with your CB350? Just trying to accumulate knowledge from those with more experience here... thanks.
 
GMX said:
For that procedure should I loosen a nut first and then increase torque, or just see if I can increase torque without first loosening a nut one at a time?
Click to expand...
More mystery to me here. If you do not loosen the nut first, then you must overcome static friction to tighten the nut further — it's hard to say how much that would be. So, I would loosen first to avoid that problem if going this route. You might mark the nuts to the head with a Sharpie beforehand to see how things change afterwards. You could even loosen and go back to the standard torque value with no increase as a first attempt.

I believe a very knowledgeable member once suggested to think about this another way that I will attempt to describe in brief. The pitch of the stud threads is known, so turning the nut by a specified angle corresponds to a certain amount of stretch (strain) on the stud. If one carefully torqued the nuts initially it would be theoretically possible to determine how much more to turn each nut to increase the clamping force by a desired amount. So, you could think in terms of an added angle and wouldn't need to loosen as long as you carefully chose and implemented the added rotation angle. It wouldn't be super hard to ballpark such an angle, but I'm not sure it could be any better than a ballpark estimate. This method would be more technical to implement.

GMX said:
Just not sure how much over I should attempt..any ideas on that?
Click to expand...
I just reviewed the FSMs for both the CB350 and CB450. The torque specification for the CB350 was only 13.02 ft•lbs, while, as you noted previously, it is 21.7 ft•lbs for the CB450. Both use eight studs, but I believe the 450 uses 10mm studs and the 350 uses 8mm studs. Complicating matters further, the four center studs are longer than the four outer studs for the 450. I'm not sure, offhand, how the lengths of the studs compare between the two motors. The point being that the desired clamping force on the gasket is what determines the torque specification and the diameter and length of the studs factor into this relationship. (I'm assuming they are made of comparable materials.)

With my CB350, I increased from 13 to 15 ft•lbs initially and then to 18 ft•lbs, before realizing I wasn't dealing with a head leak in the first place.

I would want to hear from other dohc 450 voices about a reasonable increase for that motor. I used the standard value when I put my motor together. The 18/13 ratio would correspond to 30 ft•lbs, which seems too aggressive. The 15/13 ratio would yield 25 ft•lbs and that seems more reasonable to me.

GMX said:
if your leak was not a head leak, what was the problem with your CB350?
Click to expand...
My cylinder block was vapor blasted before reassembly and my best theory is that a weak spot in the casting was compromised in the process. You can follow this link to see a blurry video of oil spurting out of the casting defect, which I repaired using JB Steelstik (Tech Steel equivalent). This link takes you to pictures of the defect.
 
stl360+450 said:
I would want to hear from other dohc 450 voices about a reasonable increase for that motor. I used the standard value when I put my motor together. The 18/13 ratio would correspond to 30 ft•lbs, which seems too aggressive. The 15/13 ratio would yield 25 ft•lbs and that seems more reasonable to me.
Click to expand...
I don't keep a log of stuff like that but IIRC, I went to 25 ft-lbs on my 450 engine.
 
stl360+450 said:
Did you go higher than standard because of the overbore and performance cams or would you do that on a stock motor as well?
Click to expand...
I went higher in part because it was the re-seal of the head gasket after initial assembly (and the engine was out because of the cracked rear fender mount shortly after the build was first finished) and I wanted to do everything I could to ensure I wouldn't have to do it again. I'll go 25 ft-lbs on the drag bike engine as a final torque too, once that happens.
 
OK Refresh my memory please..
Can the head bolts be accessed and torqued with the motor in the frame by removing the tank and upper engine mounting bracket?
Or must the motor be removed from the frame?
 
GMX said:
OK Refresh my memory please..
Can the head bolts be accessed and torqued with the motor in the frame by removing the tank and upper engine mounting bracket?
Or must the motor be removed from the frame?
Click to expand...
With the tank off, you should be able to get a short extension on the torque wrench to do all of them. I'll look for an overhead picture of mine with the tank off.
 
stl360+450 said:
Yes, I agree. The four center nuts are tighter against the frame, but can still be accessed with the tank removed.
Click to expand...
I just looked at most of my assembly pics and unfortunately I don't have a direct overhead view with the tank off, but with the top motor mount plates removed you should be able to do all of them, possibly with a short extension or 17mm deep socket at most.
 
You must log in or register to reply here.
Back
Top Bottom