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Repairing a Ford Nine-Inch Pinion Support
By Paul Savadin
During more than 30 years of crankshaft grinding, I have been asked many times to repair a surface that needle bearings ride on. For years, the only advice I could offer to customers was to go buy a new part.
The problem was that a needle bearing needs a super-hard surface to ride on or it will not hold up. The surface must have a Rockwell hardness of about 65 on the C scale. Although welding a journal on a crankshaft will hold up just fine, and you’ll rarely encounter any problem with hardness, a needle-bearing on the same welded journal will fail within hours of use.
I attempted to repair a Mercury outboard motor crankshaft for a friend back in the ’70s. At that time, I worked for Scat Enterprises in Englewood, CA, and firmly believed there was not a crankshaft I could not straighten. I was in for a big surprise!
The outboard crank used needle-bearings, and the shaft was like a piece of spring steel. We straightened crankshafts then as we do now, by peening them with a hammer and chisel. But, no matter how hard I hit it, it would not come straight. Even if I had been able to get it straight, the weld would have failed because it was not hard enough. From that day forward, if anyone wanted to talk about repairing anything with needle-bearings I told them that it could not be fixed – buy a new one!
In 1974, I moved from California back home to San Antonio, TX, and got to be good friends with J.E. Kristek, an experienced racer and master engine builder. I was racing my own Top Fuel dragster then, but spent much time at Kristek’s shop. J.E. was the chief mechanic and engine builder on Jody Smart’s Top Fuel machine. Saying that Kristek is a wizard at what he does is an understatement. He has come up with more terrific ideas than anyone I know. If it is possible to repair, he will fix it.
The most popular rear-end for a Top Fuel car in those days was a nine-inch Ford. In my opinion, a better rear end has yet to be invented. It is still widely used today, both on the strip and on the street.
The big advantage of the Ford nine-inch rear-end is that it has a bearing which supports the rear of the pinion. This support keeps the pinion from trying to crawl up the ring gear, especially in extreme use like Top Fuel racing.
One problem many racers were having was that the small area on the rear of the pinion gear, called the pinion support, would fail. The pinion support would plug into the back of the rear end housing where it would ride on needle bearings. The support would often get chewed up by the needle-bearings, because of insufficient hardness in this area.
This was a big problem. How could we stop the damage to the pinion support? We did try to weld one as we were having big success repairing journals on the billet cranks that were being used in the fuel cars. However, the welded repair of the pinion did not last one run – it was just not hard enough.
Kristek’s theory was that if the gears were hardened enough to make the pinion-support hold up, then the gears would be too brittle and would break. On the other hand, if the gears held up, left at their present hardness, then we would continue to have pinion-support failures.
His solution was ingenious and was the end to Top Fuel racer Jody Smart’s and other customers’ rear end problems. Why not grind the pinion support undersize and find a suitable material that is the right hardness for a needle-bearing? We contacted Bohles Bearing in San Antonio, TX, and they were kind enough to find us a race material that would be the correct outside and inside diameter to do the job.
Race material, the same material that is part of a ball-bearing, is very hard. It includes the inner race, the outer race, and the balls roll in between. Bohles Bearing gave us a race, part number IR-7215-C, which can be purchased at any company that stocks bearings and race material.
The standard size of a Ford nine-inch pinion support is 1.1075˝. The inside diameter of the race is .937˝. The pinion support must be ground to .001˝ larger than the inside diameter of the race which will be .938˝. Once the pinion-support is ground to size, the race must be heated with a propane torch and placed over the freshly ground pinion-support. This must be done quickly and without hesitation as the race will seize on the pinion as soon as it begins to cool.
After the race is in place and has cooled I use TIG welding to make two small tack welds at the rear of the race 160° apart. TIG welding minimizes the amount of heat. There is not much chance of the race moving, but the tack welds are good insurance that it will stay in place.
Once the parts cool, the outside diameter must be ground to 1.1075˝. The outside diameter of the race is 1.123˝, so .0155˝ must be ground off to get to the standard size of 1.1075˝. After the race is ground to size, it is ready to be installed in the rear-end assembly.
The repair race is $10 and to grind the pinion-support is $40. This repair procedure can save having to scrap an expensive ring and pinion set for passenger car use. Aftermarket race gears are even more expensive.
Through the years we have found other applications for this type of repair. One of Kristek’s customers had a damaged transmission main-shaft from a five-speed Chevy S-10 pickup. The surface that the needle-bearings ride on was very rough and ground undersize. We used the same technology used to repair the Ford pinion.
First, of course, we tried to weld it with 308 stainless rod using a TIG weld, but it lasted only a few days and went out again. Some people may call this stupid, but J.E. and I considered it research.
The second time we used the race material method and as far as I know it is still running. The price to replace that main-shaft with another carried a $500 price tag. We successfully repaired it for $100.
There is one more repair of this type I was very proud of. A customer had a 100 hp Mercury outboard motor that damaged the front main. I located the race with the proper inside and outside diameter, ground the main .001˝ larger than the inside of the race and installed it on the crank. I then ground the main to the standard Mercury size, and that outboard is running again. I charged the customer $100 to repair it, and he was very happy. I am not sure of the price of a Mercury 100 hp crankshaft, but I assume it is not cheap.
On the outboard, the front main was simple to repair, but what do you do if the damaged journal is on the inside where it is not possible to install a race? Well, I have repaired several Mercury and Johnson cranks by grinding the damaged journal .015˝ undersize and then having it hardchromed. One boat shop that I did this repair for said that the manufacturers stated it would never hold up. These repairs were done more than 17 years ago, and none ever came back. This is enough proof for me that the chrome holds up with needle-bearings running on it.
There is no reason that it should not work. Hard chrome has a 70 Rockwell hardness. That is hard! If the chrome is applied correctly, it will hold up. I use Arizona Hard Chrome in Phoenix, AZ, for all my chroming needs.
Any shop with a crankshaft grinder should be able to make the repairs mentioned in this article and make a fair profit. In my shop there are many uses for my crankshaft grinding machine besides just grinding crankshafts.
When you think about it, a crank grinding machine is a marvelous tool with much more capability than a lathe. It can grind the hardest materials known to man. My grinder has even produced reverse thrusters used in a 747 jet engine and other jet engine parts.
None of the jobs mentioned in this article are harder than basic crankshaft grinding. You may think about expanding your services to include repairs of the type mentioned in this article. It will be profitable to your shop and you will have the satisfaction of knowing that you are saving a customer big bucks and making a good profit yourself.
Repairing some ford car parts and can be hard or easy depending on the part that you are going to touch. what brand of the crankshaft grinder did you use?
by: jackmoore 10/29/2009