patsmx5

iTrader: (16)

In racing sometime you have to go above-and-beyond for reliable fasteners. Turbo bolts are well covered here, folks run high end stuff to make sure fasteners work right. For a crank bolt stock spec is probably fine. Since I ran a SC back when I put that bolt on I torqued it to 150 and put red loc tite cause SC guys strip the keyway with extra loading a lot more often than other folks. And I ran a lot of boost and a big SC, so I was pullling 100+ hp off the crank to drive that blower. Probably overkill but better than a failure from that bolt vibrating loose or stripping the key. For a crank bolt I'd rather over than under tighten that bolt, since under torque is very likely going to end like it did for the OP here.

On my converter bolts, I torqued them to 40-50 ft*lbs (7/16 grade 8 bolts) and they vibrated loose in about 10 miles! After searching some drag racing forums, the known to work fix is 80-90 ft*lbs and lots of red loc-tite. I did that, problem solved. Have a couple thousand miles on it now and so far bolts haven't moved. For the curious, that's not factory spec because factory spec on those doesn't work reliably in a drag car.

aidandj

iTrader: (5)

Sure. Overtorquing is great until the bolt yields and then it fails.

Torque specs exist for a reason. Especially FSM torque specs.

MartinezA92

iTrader: (4)

FSM torque spec is actually 3 braps.

MX5RACER

Also, re-using a crank bolt can sometimes lead to the above damage. It is a pain, but I always buy a new crank bolt when doing timing belt work.

Savington

iTrader: (31)

Ditto. The FSM doesn't specify it as a TTY bolt, but I replace it (and the key) on every motor I build. The exceptions are on my own personal motors during maintenance, since I know the bolt was replaced and has never been overtorqued.

aidandj

iTrader: (5)

Fwiw it's a $9 bolt through Mazdacomp. I bought 2. Seems too easy to replace to mess around with.

z31maniac

This.

But I'm also the type that when I completely redid the entire suspension for '90 Track rat, every bushing/bolt/nut/washer was replaced with fresh.

hornetball

iTrader: (4)

Wise. The last issue I had with my suspension was a yielding eccentric bolt. Leads to all kinds of mischief.

Landrew

iTrader: (2)

Still waiting to see what the used crankshaft I'm after looks like. Going to get my wrench tested (for free!) I'll definitely be buying new hardware. Won't be for a few.eeeks at least.

Thanks for all the discussion.

jmann

It's hard to tell from the pics, but have you tried a new key in the crank yet? Cranks are pretty hard steel.

Landrew

iTrader: (2)

I have not tried that. I will pull the sprocket and take a better look.

Landrew

iTrader: (2)

Got some pictures of the used crank I'm thinking about using. Not sure that I like it. I see some grooves and wear on the oil seal surface and some bearing surfaces look rough? not to mention there is slight keyway wear as well. What do you think ?

patsmx5

iTrader: (16)

I wouldn't use it. I'd find a good 1.8 to get a good crank out of. One that doesn't need any repairs can be found for probably 100 bucks. Maybe less if you find a good deal.

Landrew

iTrader: (2)

That's what I suspected - thanks..

Reverant

iTrader: (10)

Run away.

rleete

iTrader: (21)

That keyway is already hosed. Why start out with bad when good ones are available?

Contact Partsgroup.com. They've always done alright by me.

http://partsgroup.com/part/1994-2005...00c-bp0611300c

Savington

iTrader: (31)

That crank is a paperweight

MX5RACER

I have always wondered why there is not a better field repair for this common problem.

I was thinking something similar to what they do for GM LS motors for superchargers. Like this:
Pinning the crank pulley - LS1GTO.com Forums

Landrew

iTrader: (2)

Thanks for the tips, its either look at the parts group crank and ship to Canada or perhaps, but probably not look at the pinning options available.

jmann

So you tried a new key in the crank and it wasn't a tight fit?