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Montero SR Crank Bolt/Timing Sprocket questions

Posted By: ichneumon

Montero SR Crank Bolt/Timing Sprocket questions - 05/07/17 08:20 PM

I bought a (seemingly) nice '95 SR a few weeks back. PO seemed to be a good mechanic - had done the crank bolt previously (replaced it with an ARP one) and just did the TB and plugs.

I drove it about 600 miles until a few miles from my house I lost power steering, alternator, etc. Had it towed home.

Thought the crank bolt had sheared (of course), but it was in place and the balancer was really loose. Figured it had just sheared the roll pin, so I tore it down, expecting to do that - the PO suggested putting a solid pin in there (I figured I'd bring it to a machine shop and have them do it). Turns out the crank bolt was hand tight - I removed it with my fingers easily. The balancer and crank sprocket are pretty shot. I bought a new balancer, but as I expected that it had just sheared the roll pin, I haven't bought the sprocket yet (I do have a new crank bolt and washer on the way).

But the worrying part is that the crank threads have lots of little metal shards in them - the threads on the bolt are perfectly fine, but I think that it ate up the crank ones a little bit (there aren't whole threads, just lots of tiny shards). It goes back in, but gets pretty tight pretty quick - I'm worried about damaging the threads, so I haven't torqued on it with a wrench.

I'm obviously fine just putting a thread chaser through it and cleaning them up... but its the crank bolt. Is that ok? Would this be something that would be better a machine shop do than me?

Folks with more experience - thoughts?

Thanks.

-Eric

Posted By: ichneumon

Re: Montero SR Crank Bolt/Timing Sprocket questions - 05/07/17 08:44 PM

I was wrong - and the question has changed. The bolt is sheared - ~51 mm from the head. Did it sort of cleanly, so it wasn't particularly obvious.

I'm fairly certain that I can't extract it that far down, especially since its the ARP one.

Is the motor toast? (i.e. new crank, bottom end rebuild necessary?)

Posted By: ichneumon

Re: Montero SR Crank Bolt/Timing Sprocket questions - 05/08/17 01:39 AM

The crank bolt is 2.03" long now, ARP says it was 2.47" originally. .44" doesn't seem like that much to drill through, but on the other hand, the bolt is really dense, and it is ~1" into the crank where it broke. I talked to the PO - he tapped the crank for the ARP bolt (its a small block chevy, 13/16" bolt). So I'm definitely not going back to the updated Mitsubishi bolt.

I've drilled out exhaust studs and stuff (from motorcycles, mostly), but this seems like quite a bit deeper and far more exacting than those. And if the ARP threads on the crank are damaged (which I think they are, but its possible that the shavings were mostly from the broken bolt, but that seems unlikely/overly optimistic), I'm going to have to figure out something to do with them, too.

The truck has 212k on it and is largely in good shape (sun faded, the leather has a rip or two, rear gate doesn't lock electrically, seems to need a new sunroof motor, but all minor issues). I'm a field biologist and would be using it for longer camping/fieldwork trips - the 22re 4runner is great for short trips, but the noise, sitting position, and slow speed really wear on me for longer trips (and my gf doesn't like driving manual). I was really happy with the Montero for all but the last 1/2 mile of the 800 miles that we were together...

I see my options as:

a) buying a right-angle drill, left-hand bits, and trying to extract it (make some sort of guide - make a really nice punch exactly in the center, working from small to bigger very slowly) - I've already bought the balancer pulley and can buy the ARP bolt. If the threads aren't that botched and I can get this out, this costs me a few hundred bucks for the drill, new timing sprocket, extractors, etc. If the threads are all botched, then I figure out some sort of helicoil thing (as its already widened and tapped beyond the stock bolt).

b) towing it to a machine shop (AAA), having them extract it, tap it, and make sure everything is balanced and good. This would cost more (potentially much more), but take less time (potentially FAR less) and give me some peace of mind.

c) buy a cheap SR on CL (there are two less than $1500 near me), go through their engine on the bench (do timing belt, valve seals if needed, etc.) and swap it into mine. This would cost more, but I could recoup some selling parts. Both are high mileage though (and compression testing under the intake does not look easy).

d) have a shop rebuild my engine (or at least go through it and change the crankshaft, etc.). This would cost the most, but give me the most peace of mind.

e) buy a used or JDM engine. I don't particularly like this option (option [c] would be better, as I could get some of the money of the truck back, and have a used engine).

I really wanted to take this rig on a big trip in late June/early July, but I've got a dead reliable 4runner which I can certainly use.

I guess I should also add that I'm a decent mechanic - I've not done engine rebuilds (except on 2 strokes, which don't count), but I've done timing chain changes, etc. I don't have particularly good work space, but its not that bad either. I'd prefer not to have an immovable hulk lying around, but that's not the end of the world, either.

Thanks.

-e

Attached File
crank bolt.jpg  (2 downloads)
Attached File
sprocket.jpg  (2 downloads)
Posted By: pcc

Re: Montero SR Crank Bolt/Timing Sprocket questions - 05/08/17 03:06 PM

If the broken bolt is not rusted then it might not take much torque to twist it out. Getting the hole drilled on center will be tough without a jig though. Maybe you can use the broken bolt to make a jig then screw it in to get center hole.

Get some penetrating fluid in there.
Posted By: PajEvo

Re: Montero SR Crank Bolt/Timing Sprocket questions - 05/13/17 04:40 PM

That's a really good idea. Put the broken end in a drill press and carefully center a hole. Then screw it in and continue the hole.

I'm currently waiting on parts to do my timing belt right now on my MIVEC DOHC V6 so I understand the space constraints you're dealing with. I previously had a 3.8 crank bolt (on my wife's gen3) come apart on the highway a long way from home due to an improperly torqued/dealer installed crank bolt, with catastrophic results. The shop it was towed to (too far from home for it to be worth it to do it myself) used an insert on the crank, and was able to properly torque a new bolt in there. Its been good for three years now, and about 50k kms, so it can be done successfully.

I think so far you are going about it the right way. Good luck.

Phil
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