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Timing chain sprocket to camshaft

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doughairfield

doughairfield

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Today I was bolting the timing chain sprocket to the front of the cam shaft just now and was tightening the 2 bolts down. As I got to 20ft/lbs I stopped gaining any additional torque and then one sheered off, with most of it inside the camshaft. I followed the torque spec from my manual for the "Timing Chain Wheel to Camshaft" which I have as 24-26 lbs. ft. Did I misunderstand something here about the torque?

So where do I go from here? I've got the end of the bolt inside the camshaft, can I just use a screw extractor to get it out? Should I not have reused those bolts?
 
I don't think that the bolts are hardened and you may get lucky and get it out. Be careful to cover everything below and around it to make sure no chips or shaving from drilling cause any problems by getting in th epan or anywhere else inside the engine.

Please don't take this the wrong way, but is it possible that you may have installed the wrong bolt in that hole? If one was slightly too long, it could have bottomed out and the torque may have snapped it off.
 
I agree, I think the bolts aren't hardened. They both failed at the same amount of torque.

I'm sure that I put the bolts that came out back in. The problem lies with the guy that rebuilt the engine before me, he most likely used what ever was lying around the workshop if all the other stuff I've uncovered is any indication.

I've rebuilt exactly zero motors so far in my life so i'm trying to remind myself this is also a learning experience. I've got a screw extractor so I'm going to see if I can get that bolt out, more posts to follow.
 
Sounds to me as though you just had a bad bolt. Good thing you found it now rather than later. It should have taken much more than 20 ftlb to twist it off, even if it was jammed or bottomed in the hole. Normally they are reusable.

Unless you've already got the head on, I would probably pull the camshaft back out while trying to remove the broken bolt. Both to reduce the chances of swarf winding up inside the engine, and to be sure the camshaft can't move during the process.

I've been having better luck with left-handed drill bits than I ever had with screw extractors.
 
Doug-

Take your time with the screw extractor - those are hardened, and can break in the stud if you try to force things - a broken extractor is a tougher job to deal with too. I'm sure it won't happen, but figured it ought to be said just in case!

Randy
 
Thanks guys, the screw extractor worked. I'm going to clean the cam back up and try to get it back in tonight. I just can't believe those bolts both started to come apart at 20 lbs.

You're totally right Randall, better to find that out now than when I go to drive it that first time.
 
So my crank shaft is no longer at top dead center after all this. What's the best way to turn it to get it there?
 
Just from my personal experience with the same thing, you'll want:

A very good magnifying glass head band;

A firm hold in a vice;

A nice, new, sharp carbide bit--seriously, carbide;

A good easy out.

Another thing. I still can't explain why I had the hardest time gradually tightening those two bolts into the camshaft while keeping the sprocket square. It really was tedious. The sprocket kept wanting to rock on some angle. But I worry about everything.
 
The "average" torque wrench range in most peoples tool box is 20-100ftlbs and accuracy is best in the center of the rated torque. So, for 24-26lbs, it's at the bottom of the range and the reading can be off by as much as 20%. That said, lower torque values are more accurate with inchlbs wrenches or smaller range wrenches. I don't know what you used on yours but maybe it was just over tightened.
 
doughairfield said:
So my crank shaft is no longer at top dead center after all this. What's the best way to turn it to get it there?
Click to expand...
Depends on what kind of accuracy you want. If you are just going for the nearest tooth, then eye-balling the slot downwards should be close enough.

If you want it really right, a degree wheel and piston stop is the way to go. Put the stop so a piston hits it somewhat below TDC, then (gently) turn to the stop in both directions. Halfway between those two points is exactly TDC.

Some folks like to set a dial indicator on top of the piston, but you can still get errors that way due to the slop in the rod bearings & wrist pins. Using the stop ensures that all the play is removed from your measurement.
 
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