stripped cam cap bolts

Recall that awhile back someone had some stripped cam cap bolts. I think the concensus or at least a possible explanation was that the person's torque wrench was uncalibrated. I just installed the cams on my project bike and I had carefully chased the thread on all bolt holes with a 6mm 1.0 pitch tap. I do this on all rebuilds and don't recall ever having a stripped cam cap bolt hole thread before... Low and behold, eight of the sixteen stripped before I hit the required 12 lbs torque. The ST has the dark colored bolts and 12 lbs is the torque spec. Anyway, I spent a couple extra hours fixing the stripped thread with inserts but I KNOW my torque wrench is pretty accurate as I used a second one for several of the ones that stripped and it reads pretty much the same. If I had known that 8 of those guys would strip, I would have put 8mm bolts in from the get go.

I still think 12 or even 8 ft/lb is too much since the aluminum is very soft, particularly the exhaust side which will generally strip before 8 ft/lb is reached. I wonder if the aluminum threads get soft from age from heat or maybe there is just less threads on the exhaust side of the head. Whatever the reason, I figure 5.5 ft/lb is the spec for the valve cover bolts which are the same thread, so I do that torque and never have a problem.

I thing the real problem is people put those bolts in the head dry, over time the aluminum corodes to the bolt. Then you remove the bolt and see aluminum on it. That hole will fail soon. Those bolts should all have a good coating of assembly lube on the threads. Use the Torco red stuff.

Jay

Almost all my cam caps are heli-coiled. It's common yo strip them.
Mark

Several of mine were barely holding on so I had them all heli-coiled. Many engine builders just go ahead and heli-coil all of them when the head is rebuilt. My last head was had "nut-serts" installed in all cam cap threads (similar to heli-coils).

We've all been down that road with cam cap bolt holes. Time-serts [spelling?] are probably the best replacement thread kits going.

When installing cams, the factory method only promotes ripping the threads out.

Once the cams are laying in the head and properly timed, the best method is to start the cam caps that have the least amount of travel before mating with the head surface.

You want to set all 4 in place with the bolts in them, sticking down into the bolt holes so you can aline the two shoulder bosses on the cams properly.

Put a 10mm socket on the bolts and spin them down with your fingers.

The manual tells you to start #3 cap first. That particular cap is then pushing #2 intake valve open and putting severe strain on the threads.

Suzuki, in the GS1000 FSM, says to clamp the camsaft in place with long nosed vie grips so as not to be pulling against the valve springs.

Duck wrote:

Suzuki, in the GS1000 FSM, says to clamp the camsaft in place with long nosed vie grips so as not to be pulling against the valve springs.

1045 posted an excellent tip about that technique a while back, here´s a link to the thread in the archives:

kzrider.com/forum/viewthread.php?tid=24241

.

Some good tips. I think that someone in the past had over tightened the bolts and weakened the threads as I put together about a dozen engines a year and have never had so many go on one engine. No offense Jay, but torque specs are for dry thread and using assembly lube and a torque wrench doesn't make much sense to me but I guess you guys assemble more engines than I do. It is so darn easy to recut 8mm thread that I wish I had known before final assembly as I was too cheap to spring for a new head gasket; just used RECOIL inserts on all the stripped holes. I don't use Timeserts due to the cost... they are likely superior to Recoil inserts but they are prohibitively expensive. If I did engine work for a living, I would spring for them (6, 8 and 14mm I guess but each kit costs 3 times what a Recoil kit does).

Duck - In this case, I doubt clamping the cams in place would have made a difference. On the last cap I had to fix, the cam was already solidly down as it was the on the last two bolts to be torqued and I carefully snugged the last bolt with a wrench before using the torque wrench and it just spun the thread out. There was absolutely no pressure from the cam since there were seven other bolts already torqued. This was just strange as it hasn't happened before.

Post edited by: wiredgeorge, at: 2006/10/29 18:58

I went with sae bolts in the two that I stripped. I can't remember the size.I'm thinking it was 1/4 nc .They were alittle tight going thru the dowels ,but seem to work fine,I also use dish soap when threading alluminum,it lubes better than oil,

jay is right about using the assembly lube on the bolts ,there is going to friction anytime you run a bolt in dry antiseize or assembly lube on threads makes it easier to get a true torque reading.i use anti seize anytime i run a steel bolt into aluminum it also makes them come out easier.

How about using longer studs threaded into the cam bolt holes,and drawing the cam caps down with nuts on the studs.Then removing the studs 1 at a time and installing the proper bolts,and then torque.