Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
All parts manufactured today use tolerances. The idea behind them is to be able to get any part, manufactured in any country, and it will fit.
In the case of pistons, pins, and rods. As we know, the pin is press fitted to the rod, and has a floating fit in the piston. In this case, the engineer would specify the pin dimensions as the base tolerance. To use a typical example, that would be written on the drawing as (dia)h7. The letter/number combination being the tolerance. To get the press fit in the rod, the size of the hole would be written on the drawing as (dia)P8. To get the floating fit in the piston, the hole size would be written as (dia)F8. That would allow these parts to be made anywhere, and still fit together. Note however, that these are examples only of dimensional tolerances to illustrate the point, and do not take certain factors, eg material into consideration.
If, when a part is purchased, it needs to be modified to fit, then that part has not been manufactured to tolerance, and therefore cannot be considered to be a quality part. Theres another point here as well. As another example. To modify the hole in the rod may also throw the positional tolerances outside the limits, rendering the rod useless...Incidentally, to hone the hole in the rod is the incorrect method in this instance, if things are to be done correctly, of course.
Joined: Thu Oct 13 2005, 08:23PM
Location: Beautiful Down Town Roebuck Ontario
Posts: 227
I don't know where you get your info but the pins that hold my Ross pistons to my Source rods have no press fit anywhere. Spiroloc on one side of the piston, position the rod and push the pin thru with your thumb and install the other spiroloc and you're done.
This may surprise you but even Oliver and other $$$ rods have to be fitted to whatever pin is being used as no 2 brands of pins are the same size.
Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
Stock pins have a press fit in the rod, floating in the piston, and no clips to hold the pins in place.
Some custom pins have a floating fit in the rod, which, has been said previously, would then have some kind of bush, as well as an oil hole. These would need clips to hold them in place. Even in this case, if the parts were quaity pieces made to the correct tolerances, no adjustment would be required.
Joined: Thu Oct 13 2005, 08:23PM
Location: Beautiful Down Town Roebuck Ontario
Posts: 227
I'm not disputing that parts made to the correct tolerance won't need correcting.
When I bought my kit from 440Source Brandon told me that there were 5 different .990 pins on the market and that NONE of them are exactly .990 and no 2 of them are the same size.
So how does 440Source build a rod to suit your definition of "quality" and have it fit 5 different sizes of .990 pins?
Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
A part that is manufactured according to ALL of the information given on the drawing from which it was ordered would fit my definition of quality.
In the case of 5 different sizes of pins, the ones that do not comply to the above would simply be returned to the manufacturer or scrapped as unusable. As long as the rods are made in the same way, ie according to ALL of the information given on the drawing from which it was ordered, then the problem would not exist.
Joined: Wed Feb 24 2010, 03:46PM
Location: Moline, IL
Posts: 95
Update on this engine. Had the car on a chasis dyno during the Hot Rod power tour. The engine put out 380 hp and 420 ft-lbs of torque at the rear wheels.
Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
66NewYorker wrote ...
Update on this engine. Had the car on a chasis dyno during the Hot Rod power tour. The engine put out 380 hp and 420 ft-lbs of torque at the rear wheels.
At what engine speed (rpm) were those figures obtained? I assume they are corrected to flywheel figures. Is that correct?
