My Car News

Motion Industries ordered the bearings for the Mazda rear end. Each came from a different place and was a different brand, but they were fine. I was the most surprised that Motion Industries could find the pinion seal because Mazda changed the spec for it later. The older design has a dust seal that fits into the dust cover on the yoke.I put it all together as directed by various websites (Google ring and pinion adjustment. Here’s one: www.richmondgear.com/01instructions.html). I am assuming now, that you have read that.Some logic: the differential is OEM Mazda RX7. It has over 140,000 miles on it, and it never had a problem. It never made noise, and it always worked. It shows no signs of damage or heavy wear. It has a spacer in the pinion bearings. The purpose of this spacer is to compensate for tool wear in the manufacturing process of the housing. Since, new bearings should be within hundredths of thousandths, the factory spacer should always work.However, instructions will tell you when to read the patterns on the ring teeth and use new spacers. I fell for this. I dug up some pinion spacers I had from a Ford 8.8 I overhauled a few years ago. Even back then, I used the factory spacers without measuring it, and it worked great (I had marked the positions of everything and put it back the way it was). It lasted another 100,000 miles with no trouble. But, because I wanted the Mazda to be just right, I planned on using new spacers.I bought a dial indicator with the magnetic stand (to measure the backlash) form Harbor Freight, and I searched for an inch-pound torque wrench to properly measure the pinion preload. The Haynes book for the RX7 says the preload should be around 12 inch-pounds, and I had to ask an engineer friend if that is 1 foot-pound; It is.Inch-pound torque wrenches are not cheap rare. Sears had one, but I wasn’t rushing to buy anything there. Amazon.com had one for 300 dollars. So I got the click-type one at Harbor Freight for 19.99. It measures down to 20 inch-pounds, but I figured it would be close enough as long as I used its lowest setting and made sure it didn’t click.I started by adding one pinion spacer and setting up the preload without the crush sleeve. This way, I could check the tooth patterns without having to use up my one shot at making the crush sleeve work.I put the carriage in with the new bearings and started measuring. The book says 3.5 to 4.3 thousandths for backlash, and I was having trouble getting it set up. It never looked right. Worse, it was making patterns that were inconsistent with any instructions I could find. Finally, I realized that the teeth patterns were indicating that the pinion was too far away. Yet, that didn’t make sense because I had added a spacer. It should have been too close.After hours of trying to figure this out, I looked closer at the dial indicator. I realized it only measures in the thousandths. I had assumed that it measures in the 10 thousandths because every single backlash spec I have ever seen was in 10 thousandths (3.5 to 4.3 thousandths = 35 to 43 10-thousandths). It took me a while comprehend this: The dial indicator, which was made for this specific use, does not display significant digits for this measurement. I cussed. Then, I reset the carriage to the right backlash, and the patterns correctly indicated that the pinion was too close. So I took the extra spacer out, reset the pinion with the factory spacer, reset the carriage to the right measurement, and it was perfect with the original spacer just like it should be.I reassembled the pinion with the used crush sleeve. I figured out how to reuse it and have it work just fine (there is no such thing as a new crush sleeve for this rear end, at least not that I could find). Mazda has decided that 85 RX7s are now too old to support. I placed a small spacer, which I had left over from that Ford 8.8 kit, with the sleeve, torqued down the yoke, and it all went together perfectly.Now the car is its fast old self again.Punch line:Know what you are measuring.

People ask me for the easiest solution to make improvements to a car. They see things like Vortex Tornado or whatever that thing is goes in the intake, and it supposedly mixes the air better and improves mileage and horsepower. By the way, that is BS. The engineers at your favorite car company spend a lot of time making your intake as efficient and quiet as possible. So adding a piece of tin is not likely to help. Go ahead and try it, though, but I will be skeptical of the results. Maybe you subconsciously drive more prudently and inadvertently improve your mileage when you use one. Horsepower? Professional race teams spend a lot of time and money improving horsepower. Don't you think they would use a piece of tin if it would help? My favorite miracle product is called Marvel Mystery Oil. It is a simple additive that cleans the engine. It takes time, and it isn't really a miracle, but it works. A lot of Hondas from the 80s had a problem with oil consumption. I overhauled an engine once because of it. It turns out that overhauling the engine is not necessary. The problem was those Honda engineers made the engine too good. The tolerances were too tight for the oil rings. When they get dirty, they stick and the engine burns oil. All I really had to do was clean the engine. Marvel Mystery Oil does that. When I was at BSU, a professor asked me what to do about a Prelude that was smoking. I told her to change the oil and replace one quart with MMO, and do that every 1000 miles until it stops smoking. She agreed that changing the oil that many times would still be cheaper than major repairs. It worked. After about a year and about five oil changes, the smoking stopped. I had an 85 Mazda RX7 with the original engine for a couple years. It had about 130,000 miles on it, which is getting close to the end of its life. It ran ok, but I started putting MMO in the fuel, and it ran better. Turns out that MMO is well known in the RX7 community as the trick to better performance. Now I put it in all of my cars just on principle. It keeps them clean and they run better longer. I recently got an '89 Mazda B2600i with 225,000 miles on it. I put MMO in the gas, and it caused some deposits on the plugs, but otherwise it cleaned up and runs great. I am not saying that other products don't work. I have never tried anything else other than gas dryers. I am one of those guys who finds something that works, and I quit looking.