In the Feb 4 National Dragster, p26, the caption for the main picture shows Ben Zipf torquing the rod bolts on the Lucas Oil Top Fuel car to "approximately 90 ft/lbs." I guess a stretch gauge isn't used on at least some top fuel engines. I was surprised to see this since using a gauge so highly recommended. Any thoughts?

When you only have to have the rods stay in it for 4.5 seconds, and rebuild it after every run and have 1 hour to do it, I'd say you "just want to make sure they're tight". smile.gif

You're probably right.

Pat,

This is just a guess, but I would expect after doing it for as long as they have, you may know exactly what tq will give you the stretch you need. If it's the same material being stretched, same size, same density, etc. I would expect that the same tq would give you very close to the same stretch each time. With that much money in an engine, I would expect they know at that tq, it won't fail and will hold together.

Fred.

Granted I've only built 3 engines in my life, but I've never used a stretch guage and they all lived or are currently living with much abuse :D

In the top Fuel/Funny car ranks, I doubt seriously if there is a whole lot of "precision checking" going on in the "heat of the battle." I watched Auston Coil (Cheif for John Force), at Sacramento one time, while they "rebuilt" bewteen rounds. He sat on a chair and put new rings on what looked like new rods and pistons. He had them all in order, one at a time he "ringed" the rod/piston and handed it to another guy (whose position was on top of the engine) who put them in the holes in the order Auston told him to and another guy (whose position stayed under the car) torqued each one. Not much checking of anything! Simple, fast, and not all that sanitary either! LOL!

Taking the time to stand and watch one of those teams in the pits between rounds is really enlightening. It shows you that there is a lot of work done "at home" but when it's "race time" all they got time to do is keep it from leaking, tune it up, and keep it together long enough to get to the other end. And...sometimes they actually accomplish at least one of the three things! ;)

When they are against the clock, it is all about experience, savy and "Luck!"

Dave

Seriously, you need a preload in the bolt that meets the needs of the application, without getting the bolt in a "plastic" elongation region. I'm sure that as mentioned above, the torque they go to meets this requirement and there is a pretty good margin of error by just torquing it. My new Manley BBC rods INDICATE I can get the proper stretch in a 10 ft/lb window.

I will check this with a stretch gauge I own.

I know of several people that put an engine together that are pretty good but don't use a stretch gauge.

From what I have seen, the higher quality the rod and bolt, the more likely you can just torque it and hit intended stretch.

Can't remember the number but a TFD TFFC car only goes about 600 revolutions or somthing down the track.

Like sticking a stick of TNT in each hole 80 times...

All that was said makes sense. No doubt, they have worked out in advance what torque is needed to get the proper preload/stretch on the bolts. I'd guess that an endurance engine is more critical in this area plus they have much more time to rebuild the engine. Thanks for clearing up my confusion.

Torque and angle is an acceptable method also.

http://www.oliver-rods.com/library/libraryindex.html#Anchor-26502

For darn near 100 years since the internal combustion engine was first conceived torquing rod bolts was the norm and worked well on many a motor. How come in the last few years that this stretch thing has come into being? I'm not opposed to progress but enough is enough. What system does GM use when tightening rod bolts? Bet they never heard of stretch when they put together my 70 Cutlasses 350 that has never been apart and still going strong.

66 283,

That is an excellent read.

Fred.

Originally posted by Greg Eacker:
For darn near 100 years since the internal combustion engine was first conceived torquing rod bolts was the norm and worked well on many a motor. How come in the last few years that this stretch thing has come into being? I'm not opposed to progress but enough is enough. What system does GM use when tightening rod bolts? Bet they never heard of stretch when they put together my 70 Cutlasses 350 that has never been apart and still going strong. =

Hmm,,, Best way I can think of to answer this is they also didn't have computers 100 years ago to ask a question so easily & 20 years ago very few people carried phones around in their pocket but that doesn't necessarily make these a bad thing,,,
or does it?? :rolleyes:

And GM may not have told you but they definitely know about the stretch of those fasteners when they built your engine.
If not they couldn't give you a torque estimate to tighten the bolt to.
When you torque a bolt you are stretching it, just not as close to the capability of the fastener as can be done with stretch, Torque angle or TTY. The last being a bit scary as TTY is right on the edge of fastener strength.

Today almost every OEM manufacturer I know of uses either TTY or Torque angle on critical parts.
BTW, Torque angle is essentially the same thing as stretch, just a different way of measuring it.
Torque is a pretty inaccurate method of tightening fasteners compared to stretch but used to be quite adequate (and still is) as long as you leave enough margin for error which is what the OEM's & everyone else do when using torque only, especially when using an unknown lubricant or lack thereof.

Take a new set of rods & bolts some time & using the same lubricant torque & loosen them about 5 times & check the stretch each time you do it,, the results may surprise you.

If you want to get really confused check the specs for the 97 & up small block cylinder heads & compare them to the earlier stuff ;)