Tensioner bolt thread problem.

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Finally getting around to changing the timing belt on my 1994 ST1100. Changing the tensioner and spring as part of the project. All went well until I broke loose the tensioner bolt. Thought when it broke loose it was just the factory thread lock giving way. But it continued to turn hard instead of freely. Backed out about a turn and a half, then decided I'd tighten it back up, maybe extra stubborn thread lock. It did not want to move. So my only choice was to continue taking it out, not an easy task. Turns out the first five threads of the bolt furthest into the engine were filled with aluminum casting. Seems the aluminum casting on that end of the bolt welded itself to the bolt. Instead of the bolt unscrewing from the threads, the threads just broke off. Could not even clean aluminum from the bolt threads after bolt removed. Had to use a 10 X 1.25 die to cut the aluminum from the threads. In the course of removing the bolt, aluminum welded to the bolt end threads pretty much destroyed remaining threads in the engine casting. Ran a 10 x 1.25 tap through to clean up the damage. Guessing less than 1/2 the thread depth is left. After a little bit of investigation found there is about 1/2 inch of unused thread behind where tighten bolt would stop. Bolt screws in about 3/4 inch, total threaded depth in casting about 1-1/2 inches. Which option would you folks take.

1. Since 1/2 inch of unused thread left in the engine casting, just buy a bolt 1/2 inch longer than stock bolt, reach those unused threads and call it good.
2. Bore it out 3/4 inch depth and seat a 10 x 1.25 helicoil and use stock bolt. Wish they made helicoils in one inch or longer lengths instead of just 1/2 inch.

Maybe someone out there has something that would work better that I don't know about.
Have heard of this problem with dissimilar metals bonding together happening, but have never run into it before. I am posting this just as we are leaving for three days, so Thank You for your responses in advance.
 

Erdoc48

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Man, that’s a tough one- do you think someone was in there in the past, crossthreaded (or overtightened) the bolt and galled the aluminum? Personally, I’m thinking a helicoil (or Timesert) may be a pretty good idea. I’d rather trust threads from the origin of the bolt hole vs hoping the deeper threads hold the tensioner well- you don’t want a failure under load and have the tensioner loosen- if that happens the belt could jump and all kinds of havoc could occur. Again, this is just one of many opinions.
 
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Looks like I am the first one in there. Bike has only 33000 miles. Changing tensioner and idle pulley not because of age of parts, rather age of bearing grease. Also changing all coolant hoses, all is original. Thanks for you thoughts and concerns.
 

Erdoc48

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When I did mine recently, I left the tensioner as is (just loosened the bolt to release the tension) and then retorqued the bolt. It doesn’t make sense how that bolt on yours came out (tearing out the aluminum), but I’d still use the helicoil for the repair.

I hope it all works out well.
 
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A helicoil repair would work. You might want to consider a Time-sert also. This is a steel bushing threaded inside and out and locks into the hole....basically a permanent repair. Sometimes the helicoil will back out during maintenance and will need to be replaced. You can find Time-serts online or through Kawasaki dealers as part of their race bike repair kits.
 
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If there is 1-1/2 inches of threaded hole in the casting and the bolt screws in 3/4 inch you still have 3/4 inch undamaged threaded hole remaining. If this is the case a longer bolt would afford you the same amount of thread engagement as you had before. Assuming that you would use a bolt of similar quality and strength I would go this route as you would not loose any thread engagement or clamping force. This also leaves you with a virgin diameter hole. If you ever have the same problem in the future you still have the option of a Helicoil or Timesert repair which is always easier and more efficient on an original diameter threaded hole.
This sounds very sensible to me. Properly torqued, I can't see why the depth of the holding threads makes any difference.
 

Earl43P

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Should you decide to repair the thread bore, the Timesert is FAR superior to helicoil.
They also come in various lengths. Expensive in comparison, and you have straight line access to be able to drill it.

I lucked out and found a Timesert kit for $80 on eBay, used once.
I used it to repair a stripped oil drain plug hole on my 93 Goldwing.
 
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I'd try using the longer bolt method, if it torques to spec without spinning the remaining threads loose, I'd call it a day. If it can't hold the specified torque, then a helicoil or timesert is your only other option.
 
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Back home and thank you for all the thoughts and info. I pretty much had talked myself into just buying a longer bolt and grabbing the unused threads further into the casting. I'm sure it would hold everything tight against the engine within torque spec's. But when I went through the process in my mind, after the new belt is installed, loosen tensioner, rotate crank 2 to 4 times, then turn crankshaft clockwise 3 teeth. It was the part about loosening the tensioner that got me concerned about the tensioner bolt sagging or becoming somewhat untrue due to the missing 3/4 inch of threads towards the outside of the casting. Would this cause the tensioner to run untrue with the belt? Decided since I already had forks off, and looks like a straight shot to work with all the tools and pieces to install a timesert, I would take that route. Also ordered a 25mm Timesert so original bolt could bite into same number of new threads as it had from the factory. Don't know if you agree with my reasoning, but once again thanks all for your input. It was all valuable to me.
 
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Earl43P

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You made a good decision.
In my case, I used a dab of metal epoxy on the last few threads where the Timesert seats in the bore.
Unnecessary insurance perhaps, but it made sense at the time.
 
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All done , all is well. Thread- sert did work like a charm. Fiddled around with getting the new timing belt just right. No first time wonder for me. Forgot I had used time - sert before on spark plug project years ago. Thanks all again.
 

Erdoc48

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In the near future, I’m planning to dissect the 2000 to do the hoses and timing belt like I did on the 94. I’m expecting this time the job should go more quickly since it’s a virgin bike and no one has been in there to change any settings (I spent nearly a day on the 94 with trying to figure out why the cam and crank marks didn’t match before using cyl #1 for TDC and having the cam marks lines up). I plan to use the original tensioner since it’s a low mileage bike. Just in case, what timesert did you get? I see it’s 25 mm (I assume that’s the length. What’s the bore and screw pitch? Thanks for any information you have. I assume I won’t need one but you never know.
 

John OoSTerhuis

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The tensioner bolt appears to be a 10mm, 60mm long:

BOLT, FLANGE (10X60)
90107-ML0-700

Edit: Sorry, dunno the pitch for that bolt’s threads. Good call on using a Timesert, I wouldn’t have risked it either.

John
 
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Good call on using a Timesert, I wouldn’t have risked it either.
yeah, after I had some time to think about the damage potential if the remaining threads gave out later, I changed my mind over to the thread repair option being the only way to go.
 
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Sorry Erdoc48 for the late response. You were correct, Time-sert length was 25mm, 10mm, thread pitch 1.25. Working on a 1940 Farmall tractor of all things and have neglected to keep current on this post. Thanks everyone for your input.

Tim
 
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