fullblown

Well, I just got done putting a motor together using a Proform stretch gauge. I am now a firm believer of using this tool, to properly torque your rod bolts down. I used to torque them down just by using a torque bar and have had no problems what so ever.
However this time around, the motor that I'm putting together is probally going to see some high revs and massive HP, atleast i hope . Which makes me kind of paranoid about everything.

Manley Turbo Tuff were the rods we were using (this thing is a beast). The
Instructions called for 45ft lbs or torque of .0058"-.0062" or stretch, using their supplied lube. So I was like oh what the hell, Ill compare with my "Snap on" torque bar which is almost brand new. Here are the steps i took.....

Step 1- I loaded a rod bolt into the stretch gauge and zeroed the guage out.

Step 2- I then installed the bolt onto the rod, which was already in the motor,
and loaded the gauge onto the bolt and made sure it was zeroed out still.

Step 3- Then I took the gauge off and torque those bastards to 20ft lb first,
following with a 45ft lb torque.

Step 4- I measured the stretch and found out it was at .004ish. Which is way loose
compared to what the specs asked for. The specs asked for .0058"-.0062"
at 45ft lbs. So I decided to go in between the #'s and shoot for .0060.

Step 5- I then loosen those bastards back, and measured again to make sure it
it was still zeroed, and it was. So i torqued them to 50ft lbs and measured
with my stretch guage, and found that it went up to .005ish. I then loosen
those bastards again and bump it up to 55ft lbs, and to my surprise it put
me right where i wanted to be which was .006".

Conclusion, I know that most of you already know how important a stretch gauge is but for those who don't, I would suggest not to rely on a torque bar when it comes to rod bolts. I can now sleep better knowing that my bolts werent under torque. If you think about it, At 45ft lbs it could of been like 30ft lbs. NOW GO BUY ONE!!

The Destroyer

How much did the gauge set you back?

fullblown

i believe 60-70 dollars

Muckman

iTrader: (2)

I dont understand why torque specs arent good enough? I understand the concept behind this but as long as your using a good moly lube shouldnt torque specs be somewhat consistent or at least factor in the variables such as friction.

D@nnY

for it to be off that much your torque wrench probably needs to get claibrated

OrangeBoost

Sure the torque specs are probably perfect, but is your torque wrench?

D@nnY

I tested my mac wrench agianst a snap on one that was a few years old and it was to tight by 12 ft lbs(the snap on was off)....

my mac was brand new and had a cal sheet...they are supposed to be checked every year and set to zero when not in use

amit

the domestic guys have been using the bolt stretch method for years, its a very accurate method!

The Destroyer

It would get the doubts off my chest when doing rod bolts thats for sure.

m R g S r

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by D@nnY &raquo;</TD></TR><TR><TD CLASS="quote">..they are supposed to be checked every year and set to zero when not in use</TD></TR></TABLE>

woops

D@nnY

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by amit &raquo;</TD></TR><TR><TD CLASS="quote">the domestic guys have been using the bolt stretch method for years, its a very accurate method!</TD></TR></TABLE>

domestic guys? everyone uses this method...some people just dont have stretch gauges so they use trq wrenchs....

fullblown

Yeh I need to get it calibrated for sure, but I will always use a gauge from now on, calibrated or not.

Adi Radoncic

I don't know if you guys ever looked into this but torque wrenches are off by -+3 - 5 when you buy them brand new, and why is using a torque wrench not good enough? Well because when you torque bolts with a torque wrench all your doing is measuring friction and there are alot of variables that will cause you to get the right torque reading but really your not getting the right amount of stretch.

93LSivic

Ive been using rod bolt stretch gauges ever since I started building motors.....its the only way to go. Dont forget that most of the ARP hardware suggest you stretch them about 5-6 times before final assembly.
I should take a pic of my "measuring tool" drawer in my toolbox....some nice expensive goodies in that drawer Wont find a single strip of Plasitguage in it either

earl

There is a step you are missing here. When a new rod comes from the factory, it has been torqued/stretched to size. It is at that point that the big end of the rod is honed to size at the factory. Before loosening the rod cap bolts, you should take a measurement of the exact stretched length of that bolt. Write that down and loosen the bolt. Remeasure the bolt. The difference between the lengths should match the manufacturers suggested stretch. If not, you have some challenges to figure out. If you overtorque/over stretch or undertorque/under stretch the bolt, you will not have a perfectly round big end.
I guess the point I am trying to make is just using the stretch method does not guarantee that everything was done perfectly. I do agree that you have a much better chance for accuracy using the guage however.

fullblown

That is great to know, thanks for the advice earl. Its too late now huh? When u say the big end might be out of round, do u mean it will stay that way permanately?

earl

No, not permanent. Too tight or too loose just changes the shape. Keeping the shape round is one of the keys to good bearing life.

RMS

for guys without the stretch gauge you can get more repeatable results if you torque cycle the bolts several time each to burnish the threads (more consistant friction surface for the torque wrench to work with). and like earl said you'll get better results when you have the big ends resized, too.

stretch rules though.

JDogg

yep... in addition to the bolt stretch and torque wrenches, i always make sure the big end is round w/my bore guage when its done.

Finland

I just had my Snap-on torque wrench calibrated, it cost me $80 for the calibration and certification (plus cost of shipping), however I would never build a motor without using a stretch gauge on the rod bolts.

servion

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by earl &raquo;</TD></TR><TR><TD CLASS="quote">There is a step you are missing here. When a new rod comes from the factory, it has been torqued/stretched to size. It is at that point that the big end of the rod is honed to size at the factory. Before loosening the rod cap bolts, you should take a measurement of the exact stretched length of that bolt. Write that down and loosen the bolt. Remeasure the bolt. The difference between the lengths should match the manufacturers suggested stretch. If not, you have some challenges to figure out. If you overtorque/over stretch or undertorque/under stretch the bolt, you will not have a perfectly round big end.
I guess the point I am trying to make is just using the stretch method does not guarantee that everything was done perfectly. I do agree that you have a much better chance for accuracy using the guage however.</TD></TR></TABLE>

So, what do you do if you're replacing rod bolts/rebuilding an engine when re-using a set of rods? I.E., if you don't have the ability to measure the rod bolt length "out of the box" from the manufacturer?

fullblown

You can check with a dial bore for a round bore.