Ok so this problem is not concerning my Monte but rather my Nissan. Its an '86 300zx. Im asking here because some of you guys have good mechanic(al?) experience and I have no other "car people" to ask. I could get on the Z forums but I never know whos talking out of their butt there.

So pretty straight forward problem here. The keyway on the crankshaft is damaged. The key itself is damaged and the timing gear is damaged. I already have a new gear and key but the crankshaft is damaged. Ive already spent $5-600 (maybe more) on heads, gaskets, and everything. Theres a possibility that I can get a new crankshaft but I simply cannot afford it, if its even available. That I wont know for a couple days. Cant afford it anyway tho so..

It looks like the key rolled inside the gear around the crankshaft snout.

Anyone know of a possible fix that Im not thinking of? As always, any help is appreciated very much.

 

Thats a real mess...

Any idea what the cause is? Even if you were able to cut a brand new keyway, you'd hate to end up back in the same boat.

I imagine pulling the crank and cutting a new keyway at 180* is out? IMO thats the best option, but of course you've got more work (and machine shop time). Either that or a straight slot off the end of the crank snout for a more robust rectangular shaped key.

Only thing I can think of fully assembled like that are the 'crank pin kits' used for adding superchargers to press fit balancer engines (like the LS). Thevy got a temporary sleeve with holes in it (some are perpendicular, some are parallel at the interface plane) that bolts in place to let you drill the crank and insert a steel pin or two.

My worry goes back to the first question though - if a properly fit key is getting mangled like that, then all of the forces being concentrated on a single pin are going to be even worse (and I'm not sure if you could get 2 pins close enough to both catch that sprocket without worrying about stress interactions from the holes being too close to each other).

edit-
Another not-so-great idea - since the crank is probably hosed anyways, what about some heavy tack welds (evenly spaced around the circumference to try to balance the stresses) to hold the sprocket in place? You'll probably need a cold wet rag up around the block to keep the seal from getting too hot, but you could certainly make a more permanent connection with a welder (depending on the materials of course).

 

Ok youre giving me some ideas here. Funny how obvious some seem after someone else mentions them..

The cause, im not sure. It could have been like that since ive had the car. Watching back a video of disassembly, it doesnt look like the key rolled but rather tilted and made that dent on the snout. Everything was in "its place" when I pulled that sprocket off. There still had to be a tremendous amount of force to cause that and I can turn the engine by hand without any resistance. This whole job stems from the timing belt breaking and its an interference engine. My first thought is the valve blocking the piston while also stopping the cam gears and the crankshaft momentum... You know where im going with this. Theres a problem with this theory. Why would the piston hit the valve unless there was enough play in the belt to jump timing in which case, how could the belt hold that crank sprocket tight enough to do that much damage?

For the last year ive been chasing a power loss/backfire issue that knowing what I know now, seems like a timing issue. Never actually checked the timing. I did however, check the belt which seemed tight and looked new enough that I didnt want to change it. After it broke, I pulled it out and it was melted and stringy like you would expect melted rubber to be. Not just snapped like ive seen other belts that have failed.

I like the 180* idea. I would just have to be cautious when timing it and adjust accordingly.

I also thought about welding it but thats a last resort option. The engine has 200k and I would hate to have to replace crank bearings right after welding the crankshaft. That would be just my luck to.

I think I might try the 180* cut. You think thats possible without a machine shop? I have some bits that would make a (what looks like to me) a perfect cut.

Any other ideas and input are more than welcome.

 

It sure would be tricky. Ive personally done pinning (again on a balancer), but ive never done this or seen it done.

Getting the centerline location within a degree or two should be easy. Id just put a fine temporary mark on the block to center the current keyway on and then use an angle Guage on the crank bolt to spin it exactly 180 to mark your new centerline.

The tricky part will be getting it straight and cutting it tight as you don't want slop in it or that'll tear it up pretty quickly also from rocking back and forth. Personally I'd probably cut the crank slightly undersized and then hand fit the key with a file the last .010-.020" to mate tightly (as you can buy another cheaply if you screw it up). Id just be careful to remove material evenly from both sides so you aren't skewing timing by offsetting the key.

TBH it sounds a bit crazy, but not impossible. Worst case though you can always just abandon it and figure out a plan B if it isn't working.

 

Hey man, thank you so much for the help but since I already have this thing tore down to the block and have found a crank, I think im just going to go full rebuild. Geez what a headache!

 

I'm sure you'll be a lot happier in the end - will sure save a ton of frustration trying to make this work!