Topic: Stripped cam tower threads CB750 K2

[playbike]

Hi!
I did a rebuild on my K2 CB750 and stripped one nut from the cam tower. The one that clamps the camshaft in its place (next to the cam sprocket on cylinder 3).
I replaced the nut and the new one seemed to hold pretty well. Now I've started to wonder if I should have changed the whole stud bolt as a precaution...
The thread on the stud bolt was a bit damaged but I was able to tighten the clamping nut to the spec (9-11 Nm).

Does the camshaft put a lot of stress into the clamps? Any insight on this?

[KRONUS0100]

believe this is why they weld and reinforce the cam cover...to avoid these headaches.    if it torqued to spec and is holding....its your call.  i have stripped a few of these myself, and trying to find a replacement stud is a PITA sometimes.  I have a valvecover out now being welded up.

[wrenchmuch]

That stud experiences a fair amount of stress. Forces in a running engine are trying to lift the cam towers off the head. When the cam tower lifts you loose oil pressure to the towers as the seal made by the o ring under the tower at the oil jet is lost. There's a lot that can go wrong here if the fasteners on the cam towers are weak. Having had a cam shaft seize due to loss of oil pressure , I would replace the stud. I also use thread locker on all the tower fasteners.

[MCRider]

That stud experiences a fair amount of stress. Forces in a running engine are trying to lift the cam towers off the head. When the cam tower lifts you loose oil pressure to the towers as the seal made by the o ring under the tower at the oil jet is lost. There's a lot that can go wrong here if the fasteners on the cam towers are weak. Having had a cam shaft seize due to loss of oil pressure , I would replace the stud. I also use thread locker on all the tower fasteners.

Wrenchmuch is correct. The flexing of the cam towers occurs mostly with bigger bump cams than stock. But the intent to flex is still there.

Is your bike running? If you got that nut to tighten I'd go with it.

Replacing the stud is the proper thing to do. Breaking that stud out of the head opens the possiblity that the new one will leak. As much or more than thread locker i would use thread sealer (are they the same thing or dual purpose) on the threads where it goes into the head. Those holes are open to the atmosphere and oil can wick down those threads and make a mess on the outside.

[Leanier]

If you have difficulty finding a stud you can always make one.  I just took a high grade bolt, cut it off and tapped the other end to the correct size (I  think the side in the head and the nut size were different threads, and I wanted it as stock as possible to avoid later headaches)  It worked great, little pricey since I had to buy a $10 die to tap the bolt, but it worked in a pinch.

[MCRider]

If you have difficulty finding a stud you can always make one.  I just took a high grade bolt, cut it off and tapped the other end to the correct size (I  think the side in the head and the nut size were different threads, and I wanted it as stock as possible to avoid later headaches)  It worked great, little pricey since I had to buy a $10 die to tap the bolt, but it worked in a pinch.

I think the thread's pitch is the same at each end. But one end is threaded longer than the other. I don't remember which end goes in the head. Probably the short threaded end, as the body of the stud must bottom into the surface of the head, leaving enough height for the nut to thread on 8 turns.

And the body of the stud, if I remember correctly is slightly larger than the diameter of the thread. I think that has to do with the threads being either cut or rolled, and don't ask me which. This is probably not a sdeal breaker, as Leanier says he got it to work. But that's part of the reason it is considered a special stud rather than a garden variety stud. Mayb. OCICBW

Looking at a fish, I see there is a break at eng#2200000. Somewhere in the K2 realm. The early studs were general hardware 56mm long. The later studs carried a special part number and were 58mm long. Both are NLA.

I made the mistake of replacing those studs with bolts. They leaked like sieves.

[playbike]

The bike is up and running and seems to run very well. I added a fair amount of thread lock (red loctite) and got the nut to 9 Nm.

There's no weird noises or anything.
I'll probably replace that stud when it's time for the first oil change anyway.

It's just such a pain to remove the engine from the frame.. I've got used to working with motocross bikes with engines weighing 20-30kg. 

[lucky]

If you have difficulty finding a stud you can always make one.  I just took a high grade bolt, cut it off and tapped the other end to the correct size (I  think the side in the head and the nut size were different threads, and I wanted it as stock as possible to avoid later headaches)  It worked great, little pricey since I had to buy a $10 die to tap the bolt, but it worked in a pinch.

I think the thread's pitch is the same at each end. But one end is threaded longer than the other. I don't remember which end goes in the head. Probably the short threaded end, as the body of the stud must bottom into the surface of the head, leaving enough height for the nut to thread on 8 turns.

And the body of the stud, if I remember correctly is slightly larger than the diameter of the thread. I think that has to do with the threads being either cut or rolled, and don't ask me which. This is probably not a sdeal breaker, as Leanier says he got it to work. But that's part of the reason it is considered a special stud rather than a garden variety stud. Mayb. OCICBW

Looking at a fish, I see there is a break at eng#2200000. Somewhere in the K2 realm. The early studs were general hardware 56mm long. The later studs carried a special part number and were 58mm long. Both are NLA.

I made the mistake of replacing those studs with bolts. They leaked like sieves.

You can buy engine studs easily ,no need to make one.

[playbike]

I noticed that I can take a peek at the cam tower nut through exhaust valve adjustment cap on cylinder #3. The nut seems to holding well and oil is flowing well to the rocker shafts.
I'll just keep on checking it regularly and change the stud when I have taken some time off of rebuilds.. (3 complete engine rebuilds within 9 months. Luckily not the same engine..  )

[MRieck]

That stud experiences a fair amount of stress. Forces in a running engine are trying to lift the cam towers off the head. When the cam tower lifts you loose oil pressure to the towers as the seal made by the o ring under the tower at the oil jet is lost. There's a lot that can go wrong here if the fasteners on the cam towers are weak. Having had a cam shaft seize due to loss of oil pressure , I would replace the stud. I also use thread locker on all the tower fasteners.

As much or more than thread locker i would use thread sealer (are they the same thing or dual purpose) on the threads where it goes into the head. Those holes are open to the atmosphere and oil can wick down those threads and make a mess on the outside.

I use Teflon paste