Here's and odd thing I found today.

[86dieselburb]

Went to R&R the thermostat on my 86, 6.2 burb today. Noticed the housing was starting to leak. So decided a new thermostat was inorder also. The first odd thing was the bolts holding the housing on were 2 different sized heads. Top bolt took a 14mm socket and the botom took a 15mm socket. Doubled checked and no Amercian sockets fit.

I know Chevy was into odd-ball mix match SAE and Metric bolts in the mid 80's vehicles, so this didn't seem too odd. Top bolt came out no problem. Botton bolt, as usual with every single thermo housing I've ever messed with, busted off Luckily some PB Blaster and large vise grip got it out. Never have I had a thermo housing bolt bust off and leave me a nub to grab onto. I'm buying a lotto ticket tonite since my new found luck.

Ok the really odd part begins with my trip to the local auto parts store to get 2 new housing bolts. Always like to put new bolts when possible. Both of the old bolts have metric symbols on them, but only one bolt has metric threads. Top bolt is a 3/8-16 and bottom is a 10mm 1.50 Had the parts person baffled...lol

Anybody else run into **** like this on their Chevy before?

 

[diesel4me]

Every day since 1978....

I've had more GM's with a half and half mix of metric and american bolts!--its a PITA to fix something that needs 2 sets of tools,and special taps and dies..

I'm not sure when GM started going "metric",1978 and up models seem to be the ones with the assortment of bolt sizes and threads..it's like they had to get rid of a few warehouses of "old" SAE and USS bolts before fully switching over..and I'm not sure if "going metric" meant the THREADS would be metric,or just the HEX portion of the bolt!..

I dont recall seeing any bolts with "american" threads and a metric "head" though!..(maybe they were a size that 2 sockets fit ,like 9/16 and 14mm,and I never paid any attention to the thread pitch)...

In your case it could be someone else broke a bolt off,and had to drill it and re-tap the threads,and a 3/8" tap was all they had..but I have seen several cases of half the bolts still being "american",even on 90's and some 2000's..anything to drive the mechanics batty!..

 

[BKinzey]

I think you are saying you had metric & SAE threads on the same bolt
That would be stupid and I certainly would swap it for a 10mm 1.5 threads on BOTH sides and then just change the nut on top to a metric 1.5 thread.

I don't know how close a 1.5 metric is to a 16 SAE thread is really but could it be possible it was corroded enough that it may have gauged out that way? My second guess is the possibility it had been changed out in the past and some specialty bolt was used but wouldn't surprise me if I was wrong on both counts

 

[86dieselburb]

I think you are saying you had metric & SAE threads on the same bolt
That would be stupid and I certainly would swap it for a 10mm 1.5 threads on BOTH sides and then just change the nut on top to a metric 1.5 thread.

I don't know how close a 1.5 metric is to a 16 SAE thread is really but could it be possible it was corroded enough that it may have gauged out that way? My second guess is the possibility it had been changed out in the past and some specialty bolt was used but wouldn't surprise me if I was wrong on both counts

Metric markings on both bolt heads, but only one bolt has metric threads. I wire brushed the threads on both bolts before I went ot the auto parts store, to make sure everythng fit correctly. I had to other people at the autoparts store check, besides myself, top make sure I wasnt smoking something.

I suppose its possible that the original bolts used were 3/8 -16 SAE. Along the line somebody broke the lower and drilled and tapped for a 10mm, but why go through the trouble to turn down and thread a 10mm bolt to 3/8-16 SAE for the top bolt??? Doesnt make much sense...lol Maybe somebody at the GM plant has a warped sense of humor.

The different sized heads dont bother me. Drilling and tapping to make both the same size seems like too much work. But since I have to replace the water outlet (to pitted and its leaking) I may opt to put studs in and never have to worry about them damn bolts seizing and breaking.

 

[maynardogle]

I think all those bolts were metric in te beginning. I just did the water pump on my 84 6.2 and I didn't find one SAE bolt....all metric. I was surprosed that in 84 Detroit Diesel had built amything metric. I did note that the metric bolt threads that are all over the front and top of this engine look almost identicle to SAE bolts.....amd that if you made one go in and out a couple of times it would look and maybe even feel like it belonged...