by Don Elliott
I installed a new oil pump 8 years ago in my 1958 TR3A when I did the complete restoration and I have driven 31,000 miles since. Last year I read a story in a club magazine that someone, while out motoring in his early TR, suddenly had the oil pressure drop to zero. He stopped immediately not to damage anything, and later found out his oil pump had no pin to secure the 4-lobe rotor to the pump shaft, as shown in the manuals. The shaft was turning but the rotor was slipping. The Triumph manual (pg. 13) describes the pump as: “The small centre rotor is driven by a short shaft on which it is pressed and pegged in position”. I added this to my list of items to check, if and when I ever had the oil pan off. This April, while changing the bottom end gasket to try to cut down on the oil dripping onto my garage floor, I decided to check whether my oil pump had this pin in it. There was no pin!
I had bought the pump in 1987 at the TR shop in Chiswick, in the west part of London, during one of my trips to England. They were the only supplier with oil pumps in stock at the time. I now wonder how many other pumps like this are out there in our TR’s? Steve Redway of the TR Register reported to me that this was a serious problem in England back in the early 1980’s. A number of outlets were all selling the same reproduction oil pump and they all suffered the wear problems I discovered. Rapid wear on the lobes and worn shafts. Some were lacking pins. A number of them caused disastrous engine failures. No one would take responsibility and after technical articles in the British club magazines, the problem seems to have gone away. Steve thinks that I may have bought one from this bad batch.
We all know that the quality standards on Triumph parts years ago was lax and sometimes we would bet inferior spare parts. Today no-one has to meet any quality standards. What we get is what we get.
I examined the lower journal on the pump shaft for about 1″ above the 4-lobed rotor where it should measure 0.499″. This was worn down to 0.481″ diameter. The grooves looked like a 78 RPM record. I can’t imagine what would have cased this to wear, what with all the lubrication right there. I believe that this shaft is supposed to be hardened and must conclude that this dad not been done. The diameters in the housing were still like new at 0.500″.
The Triumph manual (pg. 16) says that an oil pump should last 200,000 miles and here was this one with a worn out shaft after only 31,000 miles. I also wondered where the steel grit had gone and what other damage had resulted from this inferior shaft on the oil pump. The lobes on both the pump rotors had become tapered due to the sloppy shaft wear. This may explain why the oil pressure, after about 15,000 miles, started to drop slowly with time. When new, the oil pressure was 60-70 psi, while very recently, the pressure was only about 55 psi at 2000 rpm, and it would drop to 45 psi at an engine speed of about 3200 rpm, just the speed I like to drive. When starting the engine, the oil pressure would take considerable time to get up to pressure and after this second or two of hesitation, there was a distinct “click” – then the pressure would rise. While the manual (pg. 48) says to expect 40 – 60 psi in to gear at 30 – 40 mph (1500 2000 rpm), this hesitation, the “click” and the reduction in my oil pressure told me that something was not right. No one could explain the “click” to me.
I decided to change the two main rotating parts in the oil pump. I made a quick phone call to one of the two largest US suppliers of TR parts. The tech specialist confirmed that their replacement oil pumps have a pin to secure the rotor to the shaft. I ordered one.
I also ordered a new big end bearing shells for the connecting rods, as the manual suggests these should be changed every 30,000 miles in order to get 120,000 miles from the crankshaft before it needs a re-grind, and the ones in my engine had 31,000 on them.
The parts arrived and, guess what? The oil pump had no securing pin in it! It looked identical to the pump I had been running for the last 31,000 miles and which had worn 0.018″. It too, like the previous one, was identified as “PRODUCT OF THE UNITED KINGDOM”. I decided that if this pump had a shaft like the earlier one, it too, may not have been hardened and after another 31,000 miles, it too would become worn.
To begin, I removed the big end con rod bearing shells and all were heavily scored after only 31,000 miles. In places, the scoring was through the babbitt and the under layer of pinkish copper was evident. I can only speculate that the grit from the 0.018″ of wear on the previous steel pump shaft had found its way into the bearings and scored them. Who knows what other damage may have been done, including the main bearing shells for the crankshaft?
This made me determined to check the hardness of the former oil pump shaft as well as the new one just received. I did this on what is called a Rockwell Hardness Tester in the Mechanical Labs at the University. Both shafts were identical at Rockwell “B” Scale 57 – 58 which means that there was virtually no hardness at all in either steel pump shaft. The lowest grade of mild cold rolled steel is about this hardness. So I concluded that if I put the new pump into the motor, the shaft on this one would eventually wear and the grit would prematurely score the engine more.
Since there was no pin on either oil pump, I pressed off the 4-lobe rotor from both shafts to find out what was securing the rotor. On both, there was about 5/16″ of knurling on the shaft to “secure” the rotor from spinning. On the earlier pump, the knurling was finer and the increase in diameter added 0.003″ to create the interference press fit. On the newer one just received, the knurl only increased the diameter by 0.001″. Certainly these shafts had never been hardened as it is not possible to emboss a knurling pattern onto the O.D. of a hardened steel shaft. Who can guess how long this little bit of knurl would work before the rotor on the new pump would start to spin on the shaft and I would lose all my oil pressure.
So I bought a 12″ length of hardened and precision ground shafting at a bearing supply shop for $8.00. This was made of tool steel which had been case hardened (Rockwell C-60), and then precision centerless ground to the exact 0.500″ needed for the pump shaft. Case hardening means that the hardness is into the shaft wall about 1/16″ but the center core is not hardened so that the shaft will remain tough. It is so hard that it cannot be cut with a hacksaw. Holding it in soft jaws in a bench vice, I cut it to the correct length with a hand grinder and then, using the same grinder, machined in the slot at the top end of the shaft where the tongue on the bottom end of the shaft from the distributor drives the oil pump shaft.
I was determined to put a securing pin in this pump to make sure that the rotor would never slip. I had to grind through the 1/16″ of hardness on two opposite sides of the shaft. Then I pressed on the new rotor and drilled a hole (0.125″) through the rotor and the new steel shaft where the hardness had been ground away. Then I pressed a pin into the hole as shown in the exploded diagram in the Haynes Manual (pg. 33) for the TR2,3,3A,4 & 4A. On new original pumps, this pin is called a “Mills Pin” and is slightly tapered with straight flutes or knurling on it to prevent it coming loose. We don’t want the pin to slide sideways in the hole and end up scoring the outer rotor. So I chamfered both ends of the hole in the inner rotor and flared the ends of the securing pin so it can never slide out.
With the new bearing shells installed, I used new hardened Grade 8 bolts for the big ends with new locking tabs, a new oil filter and I installed my new improved oil pump. I re-attached the oil pan using #3 Permatex Aviation Gasket goo on the new gasket, then re-filled the engine with Castrol 10W30 GTX. I always build up the oil pressure using the starter motor with the spark plugs removed until the newly replaced oil filter becomes full and to check that there are no oil leaks. Just on the starter motor, the oil pressure went up to 65 psi within about 30 or 40 seconds. With the plugs back in, and the engine turning over at 2000 rpm, the still cold oil pressure read 70 psi. Once the engine was up to temperature (185 degrees F), the oil pressure read the same steady pressures, even at idle. When restarting the warm engine, the oil pressure quickly rises without the “click” heard before.
I spoke to the owner of the US TR Parts Supplier who had sold me this oil pump. He says that the line that he can trace back on some parts is very difficult to track and, when he orders from his usual suppliers, he has no idea where they were really made, how long they may have been sitting in someone else’s stockroom and so on. When the shipment arrives, his telephone order takers cannot know all the time what the particular item may actually be like. But oil pumps are going to be under close scrutiny from now on.
I related to him that Dave Geller had just bought one from Oregon and it had a securing pin in it. Who knows?
You may ask why I didn’t just send this oil pump back and get another. Customs papers put us at a disadvantage in Canada. Also, I didn’t feel sure that I could get another pump with the securing pin installed. And even if it had the pin, who could assure me that the pump shaft would be of the correct hardness not to wear again in 30,000 miles and chew up my bearings.
I now feel confident that the modifications I made to the new oil pump will never result in the 4-lobed rotor slipping on the shaft and the hardened steel shaft will never wear. The lobes on both the pump rotors will not wear because the hardened steel shaft will keep all the parts axial in the housing. This also means that no grit will be produced as with the former soft shaft and the bearing shells will not become scored-at least not by grit from a worn oil pump shaft.
Most people will never have a problem it they only drive near home, or if they only drive short distances each year. Some one who only drives 1000 miles per summer will take 31 years for this wear to become evident. But I drive my TR3A many miles from home and I intend to drive it for many more years. I don’t want to run the risk of having a problem. I believe that this pump will now last me 200,000 miles as suggested in the TR manual. At 5,000 miles per summer season, I won’t have to change the oil pump again until the year 2037 – and I plan to still be here to prove it.
If you don’t want these problems or the worry, check your oil pump next time you have the oil pan off and if you need to change it, buy a proper oil pump or make the modifications described here.