Stripped Threads in Camshaft End Plug Seal Retainer Cap

I searched around on the forum and could not find anything discussing this . . .

I am replacing my camshaft end plug seals on my tacoma with the 3.4L V6 (5vz-fe) engine. As I was removing one of the bolts for the cap that holds the seal in place, it did not come out smooth, and I noticed some pulled threads in the bolt. It appears that the bolt was over torqued by the factory, or possibly a previous owner, but I do not believe that the previous owner ever had the valve covers off.

When I went to reinstall the cap, the same bolt pulled all the threads at about 50 in-lb of torque. Torque for similar bolts on cam caps is 144 in-lb. The bolt appears to be a 7mm x 1.0 thread since it won't fit in my 6mm x 1.0 thead die and is loose in my 8mm x 1.0 thread die. Due to the dowel pin in the cylinder head where these threads are stripped, I cannot tap with a 8.0 mm thread size. Has anyone else run into this issue, or have an ideas on how to remedy this? This cam seal retainer cap also seals against the valve cover gasket, so one thought is that I can just leave the bolt out since the cap will be fully captured by the two dowel pins on the bottom and the valve cover on the top. Only risk I see is that it could cause the camshaft end plug seal to leak. Any ideas?

Thanks,
Scott

 

Some pictures in case it helps.

 

Many times a blind bolt hole is drilled & tapped deeper than the bolt that will be used in it. Get the correct tap & try to tap the hole a little deeper, then get a longer bolt. The hole will already some extra threads in it to accommodate the factory length bolt.

 

Any idea how much deeper I could go? I don't want to break through into a cooling jacket. I am also looking at using a helicoil, but am having lots of trouble get the locator dowel pin out.

Thanks

 

If you go the "deeper threading" route, drilling deeper or not, look into what is known as a bottoming tap. They have less of a taper/point on the end and are intended to cut threads closer to the bottom of a blind hole at the expense of more effort to turn. This will work best if there are "some" existing threads left to help start the tapping.

 

I would not drill at all. Take something a little smaller than the existing hole & stick it down in there to see how deep
the hole actually is, that will help you determine what you may do. Blow the hole out real good & thread one of your good bolts down in there without the cap so you can see how much deeper it's already threaded. Probably a 1/4"(6 or 7mm) longer bolt will do you up fine, as you said the torque needed was inch lbs. so go easy on final assembly. I like
Permatex black sealer for oil situations so put something like that all over the plug/seal/cap & let the valve cover do a
help holding things. Should get you by hopefully. Bolt thread tap sets come in 3 types, taper, plug, & bottom.

 

I did the exact same thing last week on the exact same bolt. My steps towards a solution was this.
1) measure actual depth of hole
2) compare that to the length of the factory bolt
3) I found the hole was not much deeper than the factory bolt was long.
4) Went to napa and got a new bolt that was just about the same length.
5) the difference is my replacement bolt has threads all the way to the bottom.
6) threaded it in and out to make sure it wouldn't bottom out. But it did capture a few threads in the bottom.
7) I under torqued it and put a little extra fpig on the outside.

I was panicked when it happened and still pretty disappointed. Ultimately if it holds I guess I lucked out. Let us know how it goes as I may have to get back in there someday. Hope it helps.

 

Thanks for sharing your solution Tbuzz.

I ended up going a different route, though your solution was simpler and a probably a lot less stressful. After calling around everywhere I finally found a M7x1.0 helicoil kit (M7 is a very unusual size). It ended up being a nightmare because getting the helicoil started when the threads in the cylinder head are recessed due to the dowel pin counter bore is quite difficult. I had to stretch out the helicoil with my fingers to get the correct helix pitch to get the helicoil to start threading. I botched two helicoil installs with the second becoming jammed in the newly tapped threads due to cross threading. I was just about to push the panic button and drill out to a M10 bolt (damaged hole was already too big for M8 bolt), which would have left very thin material left around the bolt on the cap. I decided to try to thread one last helicoil, and finally got it to go. I then used loctite and torqued to 90 in-lb. I also used lots of fipg since I don't ever want to have to remove that cap again.

Thanks all for the ideas

Scott

 

Tbuzz. It has been three years since this post but how did your fix work out? I'm looking to do the same thing.

 

Good job EagleFlyer, but maneuvering a tap and install tool so close to the spark plug tubes is to say the least, a PITA, this happened to me and all I had on hand was a Help-Coil 6mmx1.0 kit, same cap, front cam seal, found that 6mm bolts can handle the torque required so used the kit I had and went with 6mm fasteners 9.9 or better, if you can find stainless they are more than adequate, fortunately it was not one of the mid caps, don't envy lol, but good work tapping and repairing those holes considering the proximity to the spark pug tubes