Oil Filter Threaded Hole

[tbeiler]

Hey Guys, went to change my oil in the 86 Aspencade, and when putting the filter housing with new filter back on, I cross threaded maybe a 1/4 inch or less depth into the hole. I stopped right away not wanting to do further damage. Damn that soft aluminum.
I'm going to order a tap and chase the threads.
The thread diameter is 20 mm but not sure of the pitch, anyone happen to know?
Thanks for any help.

[Rednaxs60]

Good afternoon Tony - take the filter bolt with you and have the shop match tap to threads.

Cheers

[tbeiler]

Thanks Ernest, will definitely do that come Tuesday, but was possibly thinking to order one online.

[Stew]

If you have a metric ruler laying around you should be able to count and figure it out. A thread pitch of 1.5 means that the distance between one thread and the next is 1.5mm and so on. If you're not sure about accurately reading the distance of two threads then you could measure the distance between 10 and do the math and be more confident of your measurements.

[tbeiler]

Thanks Stew, just dug out my metric vernier and measured the pitch at 2.0 mm. Quite confident this is correct. Guess I'll find out.

[tbeiler]

Well, I took oil filter bolt to a local industrial supply shop and sure enough the the thread is M20 x 1.5 pitch.
So much for my pretty confident guess. Now to order a tap.

[tbeiler]

So, here's the final verdict.
Ordered an M20 x 1.5 tap online for a fraction of the price that local industrial supply would have charged, also got expedited shipping for an added 20, got it today (Wednesday) by noon hour. Cost with shipping was under 50 CAN.
Got out my assortment of old dental picks to try and clean out the threads as best I could before running tap through.
Lots of Aluminum slivers from cross threading came out. Spent a good hour just trying to get the threads cleaned up with the picks.
Finally got the tap started, lined it up square, and sure enough went in without issue. Good thing it followed the existing threads and not cut new threads over the old ones. That's what I was worried about. Lots of aluminum chips, was surprised by the amount that came out. I guess over its life the threads got distorted by the bolt going in and out and wearing down from the many bolt removals over its 32 yr life.
Also cleaned the filter bolt with a metric thread restoring file that I picked up at Princess Auto. The bolt looked like new, threads were nice and sharp.
Of course I turned it in by hand before installing the filter and spring just to make sure it went in easy with hand turning and didn't bind anywhere.
Once new filter was on, filled her with oil and now she is ready to go.
Had a cold one tonight.