In the midst of a routine timing belt replacement, I had my son help with assembly. As he hand-threaded the bolt that secures the idler pulley he didn't heed the tactile warning of resistance. He put the torque wrench on the bolt, and summoned my attention when things didn't feel right. I removed the bolt and found tell-tale curlicue bits nestled between its threads. Bottom line, while the idler bolt is undamaged I believe the bolt hole has lost threads--not completely, but likely enough. My stomach sank. He feels like crap. And here we are.

I basically grasp that the situation is a setback, but not an insurmountable one. I understand the bolt hole must be re-threaded with Heli-Coil (or Time-Sert) BEFORE I can finish the original job.

I can stifle my discomfort with doing a procedure I am utterly unfamiliar with. I believe my greatest dilemma is gaining suitable access to the bolt hole, which I presume will require me to lift or lower the engine... significantly. And I presume the procedure for doing so is also violently involved.

It's about this point that I consider just tucking my tail and toss the remaining parts in a box and tow the car to the mechanics shop. But the specter of the expense of this alternative compels me to reach out for advice.

Can someone offer experienced guidance with my situation?

 

I would explore repairing the threads w/ appropriate tap to chase/clean threads. Blow out w/ compressed air before trying bolt. Bolt torque is not huge for these bolts and combined w/ threadlock, the threads should be OK to hold tensioner loads. Bolt loading is primarily shear so full bolt torque may not be necessary w/ threadlock to secure bolt against loosening. See youtube for videos on chasing threads.

See numerous youtube videos on thread repair. I would strongly consider professional help to perform this repair if primary suggestion above is a no-go.

good luck

 

Thanks for your response.

I used a brush to clean out the bolt hole best I could. I used anti-seize on the bolt before "the incident" so some of that gunk remains in the hole. How would thread-lock work in an environment with fresh anti-seize residue?

Additionally, for whatever modicum of benefit it provided me I did thread the idler bolt (with the pulley attached) back into the hole and hand-tightened it. I have absolutely no idea what torque is on that bolt presently--certainly not the Honda spec of 33ft.lbs. Honestly, I confess I feel the impulse to go with it and finish the assembly. However, I know I'd do so at the sacrifice of any semblance of piece of mind, and every strange noise or long trip from that point forward would leave a knot in my stomach.

What do you think?

 

I suspect threadlock would not work in presence of antisieze. You would need to clean the hole w/ brake-clean and allow to dry to use thread lock.

Tough call. When bolt was cross-threaded, was it completely seated or stopped early? If stopped early, many of threads may be intact. That may be why it re-threaded acceptably.

As pointed out, this bolt experince shear loads due to belt tension (small load) and some rotational loads (very small bearing drag), so high torque only serves to insure bolt stays in place. Hence suggestion to use thread lock.

It's your call. Only you can decide how much "peace of mind" is worth.

Let forum know what you decide.

good luck

 

I decided to do the "try A first, then move on to B if A doesn't work" approach. "A" in this case was "go with the threads 'as is' if the threads are passable and they can hold 33ft.lbs of torque", while "B" was "drill out the bolt hole and install Heli-Coil."

Soooo....
I evaluated the condition of the bolt hole with a digital inspection camera in close-up detail. I determined the depth of the damaged threads was limited to the first ~5mm. Viewing the condition of the bolt hole directly in this manner was critical and significantly assuaged my fears. I decided to go forward with "Plan A".

I cleaned the bolt hole with brake cleaner, twist-scrubbed it with a nylon pipe-cleaning brush, and carefully threaded in the idler bolt to act as a thread chase. I repeated this process OCD-like until the bolt threaded in/out smoothly. Then I doped the idler bolt threads with ' ', stuck it thru the idler pulley, and carefully hand-threaded the bolt to the block. I then set the torque wrench on it, held my breath, and sluh...ohhh...lee pulled the handle until the blessed "click" of success.

So no need for "Plan B". We'll see in 100,000 miles if it needs to be resurrected (I left a note in silver Sharpie on the inside of the lower timing belt cover.).

 

A very cautious responsible approach. Congratulations on a great job!

good luck