In 1985 I was assigned the engineering task of analyzing a noise problem onthe 2.3 OHC cam belt system. I learned a lot about the system and cananswer some of your questions.Question #2 first.
With the low cost of timing belts these days, if you remove the belt and its been on for more than a year, don't reuse it. However, there are a lot ofdifferent quality parts out there. In 1985 Ford released a new belt with aMerkur specific part number. It was an improvement over the previous belts and was used across the board on all 2.3 vehicles. The engineering partnumber is E5RE 6268 A2A. It was essentially a change of elastomer materialfor improved durability in a heated environment. When buying belts, I suspect that we would want just the OEM part. I believe the SVO catalogue belt is of the same material, In fact I believe that its just a different number on the same belt. The tension specification is 60 to 90 pounds tension as measured by a tensiometer, or other device. I have previously posted the belt procedure (archives)Now it is where the assignment became interesting. After visiting the plant and watching the belt placement and tensioning process for some time, we understood that the tensiometer was not a good wayto measure tightness. I did some research and found a micro wave measurement device that would measure the vibrating frequency of a plucked sting, that would also measure the belt ACCURATELY. And it was repeatable.The gage was not....The problem that we had was called belt wimp, and was experienced at below900 rpm. We had not heard it on the turbo because idle speed is at 900 and the noise became prominent at around 750. Just the idle speed of the Ranger EFI. The noise originated in the short span, between the crank pulley andthe aux shaft pulley. Belt tension measurement is mid point of the longspan.With this microwave equipment we went back to the plant and measured morethan 100 engines at random and recorded the belt tensions. We then measuredand recorded after hot test. we found that belt tension had degraded to a point that those were originally set low, now fell below the 60 pound tension figure. Back in the lab, I replicated several of the tension scenarios and found that the engine that had belt tension set below mid point of the specification often fell below the specification after justsitting for 24 hours, never mind running the engine. Turning the engineover two times caused about 80% of the loss to occur just in taking up theslack in the system. (thats why turning the engine over is in the procedure). We found that after running, belt tension could be in fact as low as 40 pounds. There is no data left, I am quoting these numbers from memory, and in spite of my joking about total recall, its Glenys blessed with that, NOT ME.....So, my point is, Its my learned opinion that the belt tension will significantly decay, and low tension will produce a noise, and that very high (over tightened), will cause bearing durability issues with the stocktensioner. (the weak link in the system.)(Esslinger has an improvedtensioner)This leads to my opinion that we can and should check belt tension periodically. I released the microwave equipment for the plant to utilize and wrote aprocedure for this alternative, but was moved off to the sealing assignmentand do not know if they followed thru. Actually, the good that came out of this for the plant, was to know statistically that they were arriving at a known belt tension, and adjustingthe process to be at or near 80 lbs.The accumulation of data I had indicated that the tension would never fallout of the specification.The noise was gone. An interesting point. The guy that originally set the spec of 60 to 90 lbs.(probably someone at FOE, that did so on the 2.0 Litre)was SPOT ON. I am impressed. All that is lost though, We don't even knowwho did it....or how......do you suppose it was real engineering?
Round vs. Square tooth belt
The Ford engineer that made the change to the half round tooth has answered my query and I report as follows.
The change was made to address a whining noise and 150K durability objectives.The belt is a HTD 2 design and in addition to being quieter, will transmit more power. The valvetrain though has been changed (roller cam, ed) to require less, not more power so this design will last significantly longer with current valve train design. The change was made only on Ranger truck, and the year following the material was changed to NBR (Nitrile Buna Rubber) that also extends the life of the system. I have no specific information relative to 150K life, but everything is in the direction of goodness. Now, changing to the new design should not be considered unless your valve train load requirements are extremely high. Even net lifts of .5 and .585 do not require HTD.
I made the change, and in fact use a belt that is 1.250 wide, but then I lift the valves to .735" and turn the thing to over 8500 RPM. Different kind of animal. Relative to 150 K durability, I don't know how they maintain belt tension.
For my own use, checking/adjusting belt tension would be an annual event.