CH18s Command with stripped threads

[garydee]

I was finishing up putting my CH18 Command engine back together after replacing the coils and the head gaskets, when I had a big problem. I was installing the flange bolts for the rocker arms, torquing first at 5 foot pounds, then 10 foot pounds and just before I got to 13 foot pounds I heard a little pop! The torque wrench gave way... I knew that I must have stripped the threads in the mounting hole!

I took the bolt out and found several spiral wrappings of aluminum around one section of the bolt. Indeed, I stripped the intake valve mounting hole threads! Well, a little later on, I checked the depth of the mounting hole and discovered that the the threads went deeper than the existing bolt, so I purchased a replacement flange bolt that was about 1/4" longer. I installed the bolt with red locktite and tightened it to about 5 foot pounds. I'm hoping it will be enough to keep it from pulling out when that engine gets to crankin'!

Has anyone else ever stripped the rocker arm threads in the mounting hole on a command engine? If so, how did you fix the problem? I don't want to replace the head, just looking for a simple solution that will hold the arm securely.

[Billy-O]

I dont know if anyone else may chime in with a similar problem as you described and have a solution.... but, maybe, it might be worth looking into a "timesert". But it ain't cheap.

[dale c.]

i've put helicoils in a few. 6mm iirc.

[garydee]

I chased the threads and used longer bolts in the somewhat stripped head to remedy the problem. Seems there is quite a bit of additional thread beyond the length of the standard bolts that hold the rocker arms in place. Both rocker arm bolts torqued up to 13 ft. lbs, so I'm going to leave them alone for now...

I have on order an M8 x 1.25 tap and a 6.75mm drill as well as some M8 to M6 thread inserts that are 20 mm long just in case they are needed. They install easily with a screwdriver. Thread lock can be applied.

After doing a little research I decided against the helicoils because they are relatively short and because I didn't like the idea of breaking the installation tang off and having it stuck in the blind hole. This would leave the option of using longer 6mm bolts to provide more torque a likely improbability.

The Time-sert bushings seem a little too expensive and they are short as well. I think I have a good option with the 20mm long thread inserts. Should be easy to drill out, tap and install if needed.

[garydee]

Here are a few pictures showing the drill, tap and M8 x 1.25 to M6 x 1 bushing to repair stripped threads in the CH18 head for the rocker arms. The bushing is 20mm long and made of stainless steel. You can get everything from Amazon as needed.

Because I found that the mounting hole in the head was deeper than the original bolt, I opted to purchase a longer bolt to address the stripped thread (on the intake valve) before performing surgery on the head mounting hole. Everything tightened to the specified 13 ft. lbs. so no operation was needed. So now, I have the "fix" if something goes wrong...hopefully nothing will.

I reinstalled the engine back into the 1864 after replacing the head gaskets, exhaust valves and coils. I cleaned all the carbon off in seconds using walnut shells in my cabinet blaster. Cleaned other parts as well...Seals, gaskets and misc. parts were replaced 4 and a half years ago.

The engine started up after a little cranking to get some gas to the carb...she purrs like a kitten! 'twas a great feeling after all the work!