Oil Pump Drive Comparison

[60dgrzbelow0]

I spied what looked like an Oil Pump Drive for the GM 3.4L V6 engine on eBay for under $20.00 (S&H Included) and since I could never find one anywhere when I tore down the GM 95 3.4L, I went through a lot of trouble to disassemble the stock one from this engine and wound up cleaning out a mound of carbon, gunk and crap that was trapped in the upper bushing chamber, I decided I might as well grab this one while I had the chance. (even if the seller was listing it for an '04 "3.5"...whatever that is)

I thought that since they looked so close in design that even if it had a SBC style slot-drive in the end of the helical gear like the newer ones, I might at least be able to drive out the spring pin and try swapping the gear ends if it looked as good as it did in the picture and everything matched up elsewhere. To my complete surprise...the damned thing had a Hex Drive end on it that matched the stock TRW Hex Shaft...and in all other repects...it was a dead-balls-on match to the one I removed from the VIN "S" motor. Almost...

And so I'm asking the more seasoned members of the forum to eyeball these photos I took and tell me if these very slight variations I noted are something serious to worry about. My concerns are as follows:

(1) The distance from the upper portion of the "O" Ring groove sits about 1- mm lower down than the stock OPD.

(2) The top to bottom length of the geared section is slightly longer than the stock OPD and seems to have been cast, rather than machined from a heavier steel piece like the one on the stock OPD and it tapers a bit more down to the female Hex end of the gear piece. The gear teeth, helical angle, depth and number (13) are almost identical, however, they are just a smidgen deeper on the late model OPD, too.

The two OPDs appear, in all other respects, to be identical, including the fact that the Hex Shaft heights on both are exactly the same when fully inserted and with both units placed side by side on a level surface. I would not bother with all this, but since I'm putting so many other new and upgraded parts in this engine, if I can upgrade the Oil Pump Drive as well at the same time, I'm very inclined to do so. The last consideration is that if anyone is seeking an alternative GM OPD to replace one that is either worn out...or not to be found anywhere...then this one might do as a perfect stand-in in its place.

Thanks for your ideas on this...

-==Bob==-

[60dgrzbelow0]

Since I can only add three images per post...here is that last of the set of four OPD Comparison images...

[60dgrzbelow0]

For some reason...I was unable to "edit" my last two posts...but I wanted to confirmd that both OPD units have exactly the same number of gear teeth at thirteen (13). Okay...the edit feature is working again...

[IsaacHayes]

Not sure with the difference in metal color (one hardened more?), but the edge of the o-ring groove shouldn't matter at all. The gears are close enough either should work I would guess.

04 3.5 would be a 3500 LX9 non VVT.

[60dgrzbelow0]

Isaac...

Cool Beenz...

I think what I will do is drop the new one into the motor to see if I can eyeball it from below how well the OPD gear shaft and camshaft teeth mesh... and with the motor turned upside down on the stand, then I can push the new OPD down and out of the block from underneath, without the usual hassle of not having any place to grip the damned thing to get it out after it is installed. If it feels smooth going in and out after being coated with some Mell-Lube, I think I'm going to go ahead and use it.

I wish somebody had the specs on how these things are made because the newer one looks like the gear assembly was made out of "Mystery Metal". I did put them both in close proximity to a strong ND magnet and while it showed strong attraction to both, it seemed to respond from a distance further away with the newer model OPD, I suspect that it is probably made of either cast (because of its rough appearance) or it even might be forged, since the other unit has a well-machined surface with very fine tool lines all over it and the newer one only displays evidence of machining on the gear teeth. I should also mention that the original Hex shaft that came out of the (darker) OPD unit was all beat to Hell and worn from heavy or hard impact contact inside of the female Hex end. It looked as though the OPD Hex shaped housing containing it...was trying to strip the "Hex" right off the shaft...but only succeeded in flattening the true hexagonal faces on the shaft just a little bit. I noticed that the new, unworn TRW replacement Hex shaft fits more snugly in the newer OPD as opposed to the older unit, where more play was evident.

I wonder why they opted to use a decade old OPD design for the '04 3500 engine...saving design costs...maybe?

[ForcedFirebird]

Becasue of the expense of gear hobbing equipment, I doubt GM would change the gears.

The cam and crank centerline didn't change on the 3500 (or even the 3900 from what I gather/experienced).

The difference on color is the difference from the amount of carbon that has been introduced into the metal. Right after heat treating, everything is black because of the carbonized oil bath and the metal changing color during heating. This same phenomenon will stain the surface of the used parts in the same manner. Ever taken apart a motor with only a few thousand miles on it? All the parts are new and shiney

It's only surface carbon on the old one, and probably would have been fine to reuse, but $20 I guess isn't bad. I have several of them laying around from both the iron head and 3500's. When you need stuff like that, you should post in the buy/sell/trade section - evilbay is your enemy :P

[60dgrzbelow0]

Will do, John...

I meant to tell you that when I finally finish putting this engine together, I might wind up with as many as two sets of the forged connecting rods, some with pistons and wrist pins still intact. Some of the large ends of the rods show damage from an engine that had a failed main thrust bearing on the sides and that is where a few con-rods got grooved and damaged. If you can use them, let me know by sending me your south Florida business mailing address to my forum email address of: at60dgrzbelow0@yahoo.com and I'll box everything up and send them your way... you are welcome to them at no charge, whatsoever . Let me know if you want the old 3.4L pistons and wrist pins left attached to the one set. If not, I'll press them out and just box up the rods for you. Let me know what you think.

--==Bob==--

[ForcedFirebird]

I appreciate the offer, but right now (like most of us here) have more than enough "stuff".

Just suggesting you ask the community before buying elsewhere

I think I have 30 rods/pistons from 3500's, a 3100 set, 2 3400 sets, 1 3.1 set and 1 3.4 set, 3.1 block, 3.4 block , 2 3500 blocks, iron heads, iron head LIM's, 3.4 and 3500 LIM's, several UIM's, engine harnesses, ECM's, blah blah blah.

[60dgrzbelow0]

Okeedoke! (So many Parts....So little ROOM! ) LOL

[Skutt]

This reminds me of an experience from a long time ago. I was working for a friend who had just started a small road construction business. The single axle dump truck needed a new engine. Earlier David had pulled the 330V8 out and dropped in a 390HO. The 390 was great for about 6 months but it being a car engine and not built heavy enough for commercial use it was about done in. I was given the job of rebuilding the 330 since it was designed for trucks and could take the punishment. The 330 industrial engine and the 390 car engine were taken from the same block so they were quite the same in many respects. I was doing the work in a shop on the dock in Astoria, Or. The longshoremen would come through and watch my progress as I built this motor. I finally had it all painted up Ford blue and installed in the dump truck ready to start for the first time. Standing on the floor of the shop I reached in and turned the key for the first time. I had painstakingly made sure all was ready for this first try. The ignition timing was as close as I could get it without the engine running, the carberator was filled with gas, all was perfect. The engine started like a Chevy, the crank couldn't have turned one complete revolution and it was running smooth and all was good. All I had to do was set the ignition timing correctly now that it was running and it was ready to go. The longshoremen were impressed. Several had engine projects they wanted me to do for them.

The problem came about because I had compared the two distributors closely. We had just done a fresh tune up on the 390 so it had new points in the distributor and was ready to go. The distributors were identical in all details. I dropped in the 390 distributor and like I said it ran perfectly. The next day David took it up on it's first job with the new motor. It didn't last one day before it lost oil pressure and ruined the engine. Turned out there was a very slight difference in the size of the socket in the bottom of the distributor shaft that drove the oil pump and the shaft stripped out. I pulled the engine and did a second rebuild and all was well with the world again but not one longshoreman had me do an engine now. Anyway the moral of my story is look very closely at all details of your OPD, VERY CLOSELY!

[60dgrzbelow0]

A wise and well-told tale Mr. Skutt... Indeed...I will be taking your sage advice, along with an abundance of caution here. My inclination to use the later model OPD is based upon the fact that the the brand new TRW hex shaft fits nice and snug and perfect inside the newer version than the old one felt with either the original, battered Hex Shat or the new TRW Hex Shaft. It was the original OPD that was making every possible effort to pound against and round off the six side faces of the old hex Shaft after churning oil like butter for nearly 100,000 miles of wear and tear.