e30antonio

I'm doing a timing belt replace and I got to the point where I need to remove the crankshaft pulley. Using a rented pulley-puller from Autozone, the pulley came off slowly.

With the crank pulley now off, I tried put the crank bolt back in, but it won't go back in. The bolt itself is fine, but the first 3-4 threads of the crankshaft hole look like they were flattened out by the puller.

From what I understand, my best bet is to use a thread chaser, but what size thread do I use? How do I use the chaser without making it worse?

Edit: Crankshaft bolt size is M18x1.5 as determined by a local fastener store.

YODAONE

Several basics you can do...

You hold the bolt in your hand, so why not determine metric thread size and pitch from that?

Second, based on your questions. it appears you have not performed this type of repair before...

You will.require several specialized tools to successfully effect this type of repair which are not available at AutoZone(d)

Why take a chance ruining the threads beyond repair??

Locate professional to perform repair.

Also...what method did you use to loosen the crank bolt? Starter impact? Strap on outer harmonic balancer pulley?

e30antonio

There's no way I can guess the exact size and pitch from looking at it. Measured, it looks to be 15/16" or 23.8mm.
I loosened the bolt with a long breaker bar.

timmy0tool

iTrader: (7)

I think what yodaone meant was to take the bolt into a hardware store and see what size and pitch of a tap you need to chase the threads back to normal.
likely you will need a very large metric tap!

LeX2K

You need a thread gauge most any bolt supply will have one, or get one from Amazon. Of we could make a good guess if you tell us the bolt diameter, both the bolt head and threads. You are saying the thread diameter is 24mm?

e30antonio

Yes, from my free-handed measure with a measuring tape, it was 15/16 / ~24mm. I cannot find the specification for that bolt anywhere online. I will try to get a local store to measure it tomorrow.

LeX2K

You can figure it out yourself count the number of threads then measure the length of all the threads in mm. Divide the number of threads by the length, you will get something close to 1.25 or 1.5 that will be your thread pitch in mm.

dashan

Use a dremel to work the thread out, not a difficult job. I did the same on the thread of a muzzle brake.

e30antonio

I had it measured at a local fastener store. The crankshaft bolt is M18 x 1.5. Now the question is, what type of tap to use? A regular cutting tap? Chaser tap?

Here is a pic of the situation. The silver ring between the two green lines are the flattened/destroyed threads that the pulley-puller ate. They go concentrically around the whole hole. (meaning it's not just what you see in the pic that's destroyed).

YODAONE

Now, how to securely hold the crankshaft firmly in place (without distorting it or another engine component) while you or your technician is chasing the threads...

One possibility is to install the harmonic balancer and affix a special service tool (the shop manual specified tool) used to hold harmonic balancer in place (without compromising the rubber harmonic balancer ring) while loosening or tightening the crankshaft bolt.

See:

https://www.clublexus.com/forums/ls-...tml?styleid=20

Of course, this will require use of a longer tap...

LeX2K

Use an impact to tighten the bolt. If it was me I'd use a tapered tap, done it many times on cylinder blocks.

oldskewel

iTrader: (1)

The challenge you have regarding a tap is that you want it to cut new threads that are synched with the remaining threads. A tap that is slightly tapered should hopefully let the tip of the tap get itself aligned with the first few remaining threads while the rest of the tap cuts the new threads in the messed up portion.

Most normal taps are like this - tapered, so they ease into the cutting gradually. A blind or bottom tap would not be this, so you don't want one of those. Just a regular tap will be fine.

To give a little more info to make sure the person selling the tap is not confused ... there is such a thing as tapered threads. Used for pipe fittings. You do NOT want a tap for tapered threads - those do exist, and that's not what you want. You want a regular (tapered) tap for straight M18-1.5 threads. For those, they are tapered at the tip and then go straight. A tapered tap for tapered threads is tapered all the way. Really. LOL

And when you actually use the tap, make sure the new threads are synched with the existing ones before you get too far. And I would cut any more threads than you need to - e.g., do not think that since you paid good $$ for this tap you're going to tune up your crankshaft. No, do as little thread cutting as needed to get the crankshaft pulley bolt to thread back in there. Cutting fluid on the tap would be ideal, but if you don't have that, WD-40 or motor oil will work fine. A special purpose tap holding tool will also be ideal, helping you to keep things aligned properly as you carefully cut the threads. But workarounds are possible too.

And those last ~2 threads you mangled are not needed. If you could easily remove them using a drill bit, Dremel, etc. that would be a fine solution too. But I think the tap will be the most likely to succeed here.

LeX2K

You sure the bolt is m18 and not m19? Get a piece of plastic or soft wood (or aluminum if you can) and make some thread with your tap and thread in the crank bolt to make sure. The crank is fairly hard so don't force the tap if you snap it off it's game over.

e30antonio

Thanks everyone for the advice, I'm taking it all in.

One last question before I go at the crankshaft with my tap...could I get away with filing the threads on the crank BOLT to make it match with the screwed up threads? The logic I see here is that the bolt would be way easier to replace than a crankshaft.

timmy0tool

iTrader: (7)

I see your logic but filing the bolt itself is pointless since the mating end at the crank is still messed up.
if you file the first 2 threads of the bolt, the next 2 threads will mess up as you tighten into the crank, and so forth until you have no threads left on the bolt.
or the bolt acts as a blunt tap and eventually correcting itself but at the cost of a few more messed up threads - not wise!

a tap to the crank is your best option here and go slowly, going in at half turns, then backing out a quarter turn, then in again a little deeper, until it threads in smoothly!