My 1974 GTMX's resurrection is coming along; though slower than I'd hoped.  There's no longer any rush with a foot of snow here already and another 5" on the way.

The bottom end is together after replacing a broken transmission output shaft and some necessary machine work to remove and replace its damaged bushing at the kick start idler gear end of the shaft.

The bike's autolube system was disconnected and plugged off for the 40+ years I've had the bike but I never knew why.. We always used pre-mix fuel, but I'm now in the process of getting the autolube system back up and running and have learned quite a bit about the auto lube system.

First issue is a missing oil pump "guide pin".  From what I've seen in pix and videos, the guide pin is a slotted roll pin but I cannot find it shown as a replacement part in the 1974 GTMXA Parts Manual that I have.  Best I can measure the hole and guess at the length, I'm thinking a standard 2mm x 10-12mm slotted roll pin should work.  Can anyone confirm that I'm on the right track with these dimensions?  Or perhaps have a spare pump and guide pin to measure?  I think all the Yamaha oil pump guide pins should all be the same.

Once the pump is re-assembled and adjusted, I'd like to verify the pump is actually producing the specified output.  I've now familiarized myself with the procedure of measuring oil pump output oer 200 turns at idle and WOT; but I have been unable to find the OIL output specs for the 1973-74 GTMX GT80 GT1 pumps.

I have copies of Yamaha SB's 258 but as @MarkT posted in another thread on a DT250, that SB only goes up to 1971.  See below...

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MarkT post=148787
Here's what I found quickly.  Up to 71 and then 1974.  I also have later.  Didn't really find 72-73 data but should be out there. In any case this should give an idea of what to expect for output hopefully. 

  

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Being unfamiliar with most other Yamaha Model designations, I'm hoping that someone can point out any similar 80cc engine models in the first 1969-1971 chart above, that would likely have the same oil output requirements as my 1974 GTMX?

I'd also be interested where @MarkT obtained the second chart on the DT250?  Was this data specific to the DT250/360 models?  Or did the data cone from a later (1974) similar SB that might include oil output data for other models like the 1974 GTMX, GT1, GT80, etc.?

Any help, suggestions, or advice is much appreciated!
ZT

The early manuals often gave a bit more information on part dimensions .
My DT1 B manual lists the guide pin as being 2.5mm x 11.8 mm .
You were pretty close with your estimation .
I'd expect the same pin was used on all of the autolube pumps in that era .

Thanks Swoop!  I appreciate your help!

What year and how many CCs is your DT1?

DT1B is a 69 250 .
As for your pump output specs . The HT1 90 would be a reasonable comparison .

Thanks again Swoop!

As I mentioned above, I cannot find the oil pump guide pin as a separate replaceable part in the 1974 GTMXA parts catalog I have.

This a long shot but, assuming the guide pins are all the same, I'm wondering if the guide pin does appear in other parts catalogs/other models. If so, can someone post the Yamaha part number?

recognize that 2nd chart from 250/360 service manual.

"recognize that 2nd chart from 250/360 service manual."
Bummer!  But thanks for the info, pabdt.
Does anyone have a Yamaha part number for an oil pump guide pin?

I just came back from Ace Hardware with a 3/32" x 1/2" "tension" pin.  That worked out to 2.38mm x 12.7mm so, based on the 2.5mm x 11.8mm Swoop posted above, I had high hopes.
I don't do many roll pins, but I don't think the pin from Ace will ever go in the hole in my pump cover.  The relaxed diameter of the Ace pin was actually 2.5mm and the hole, understandably, not perfectly round; measures 1.96 to 2.06mm with my HF caliper.

Again, not being familiar with such things, can anyone tell me if a 2mm roll pin should have an uncompressed diameter of 2mm?  Or something larger to be compressed and pressed into a 2mm hole?

Pin number I've used is 91608-20010, it wasn't a GT80 pump though and I don't know how many different pins they might have used.

Make sure you don't press pin in too far or it will jam the pump plunger.  

Here are specs for 1978 GT80E and 1978 GTMXE, same engine, should be close.  


 

Member DEET is an oil pump expert (he probably won't admit it though) and likely has the pin you need.  He can also rebuild the pump (and do it correctly!) for a reasonable price.