stretch gauge - how to??
 

OK,first off, this is the first time I'm trying the stretch gauge method, I've always torqued, and it's a 944 engine, which shouldn't matter.
1st:
ARP states the stretching method is preferred, so I purchased a stretch gauge. Now, I'm trying to figure out how to install the guage. The only way the gaage mounts is to the top and bottom of the rod bolt. As soon as I let go of the gauge it wants to fall off. I bought the summit racing gauage:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D900015&N=70 0+%2D113071+115&autoview=sku

2nd
The specs call for 0.0110 to 0.0114. How do I read this on the gauge. I'm assuming the dial makes 1 full rotation and then to the 10-14? Here's a pic of the gauge:
http://forums.pelicanparts.com/uploa...1161537704.jpg

Are you pre-loading the gauge on the bolt? To stop the gauge from 'falling off' pre-load the gauge .30" - gauge won't fall off now and you can measure your necessary stretch.

AM

OK, explain it to me as if I was a 5yr old. Remember, this is my first time dealing with guages. When I put the guage on I have to lift the top knob in order to lift the needle up on-to to the top of the bolt. When I release the knob it's at 30. Is that .30"?
Maybe my first step is learing how to read a guage?

Hi Armando - The gauge should show about .3" preload.
I'm pretty sure the gauge you have is 1" travel, so the 30 mark on the outer dial is .03". To get .30", the small dial should show '3' See the picture below - hope it makes sense :)

Regards,
Andrew M

Forgot the Pic!

http://forums.pelicanparts.com/uploa...1161548997.jpg

As well, I'm pretty sure that to get .0110-.0114 stretch, you are just getting the gauge go from the 0 to the 1st mark after the 10 as each mark is .001.

ie- go 11 of the marks and you have your .0110.

If you went all the way around the dial during the stretch tightening, you would acutally be getting .110 - way over stretched.

Hopefully someone else will chime in and give you a second opinion to verify that I'm correct or point out any errors

Regards,
Andrew M

http://forums.pelicanparts.com/uploa...1161549405.jpg

So I should use the small dial as the preload and the big dial as the actual spec? Makes sense. I'm sure glad I'm learning this on my 944 engine before going into my 911 engine.:)

Exactly as Andrew says. Each mark on the big dial is 0.001".
Do not overstretch them...shoot for the low end of the stretch (I discussed this at length with the ARP tech staff).
BTW, the Summit gauge is dfficult to use, it does like to fall off. I was a machinist for ten years, and this gauge is tricky.

Yes, I'm finding that out. It still keeps falling off, even with the preload. I'm going to devise a way to make it work. I wasn't planning on building many engines so I opted for the cheap guage. You get what you pay for.

Armando,

Can you show a picture of the whole stretch gauge, I too just bought one and mine has a lock nut on the threaded screw which keeps the bolt from backing out. Mine has accurracy down to
0.0005" and the dial is adjustable when loosening the dial lock. It stays on really well but I can't start my project yet because I screwed up a nice new set of rod bearings. I just purchased another set so I plan to do it asap. I'll post my pictures and results as well. Oh, my project is a 3.2l Euro 76 911 Carrera.

Good luck,

Alex

Alex, did you buy the summit racing one? First thing I learned was that it can't be mounted vertically. The weight of the guage pushes down on the assy. If you mount it horizontally, gravity makes it slip. I may have to find a way to mount it to the block. Or, I may just torque the bolts down. I'm not getting a warm and fuzzy feeling about the stretching method, at least with the tools I have.

Armando,

It may be that you will have to measure, remove gage, make a 1/4 or 1/8th turn and remeasure. A PITA for sure, but if your gage will not stay on whilst you turn the nut...

Either that or call Summit and say the thing cannot be used for your application and you are retuning it :) Good to know that I shouldn't buy that one though :)

Best regards,

Michael

Armando,

I did not purchase a summit one, I have included a picture of the one I bought. I use a lot of gauges at work and this one feels pretty good. My ARP bolts have dimples on both end of the bolts that allow my gauge to lock in under slight pressure. It's true the entire assembly is long and will slide down somewhat but it should not affect my stretching. I will send more pictures of the guage installed over a bolt. I understand your concern but I abandoned the torque method after complete assembly of all my rods onto my crank....I did not feel too good about it even though I premeasured all my rod bolts with a precision micrometer. I think the stretch approach is the best even though I have the least experience with it. Don't give up yet, you and all of us most likely have too much invested at this point to have any doubts.

Best Regards,

Alex

http://forums.pelicanparts.com/uploa...1161614271.jpg

A good stretch guage will have extra strong springs in it so it will not tend to fall off the bolt. But if yours is weak, you can still use it, its just that it will be a bit of a pain. Make sure that the initial reading is not lost, ie don't reset the micrometer. Tighten the bolt, hold the guage in place and get a reading. Do the best you can, its still better than torque which can and is often off by as much as 50% in terms of stretch, which is all that counts.

Screw it, I torqued them down. I called ARP and verified torque specs. I did measure the bolts before and after torquing, all 3 times and came out with the same measurements:

Before torque: 2.955
after torque: 2.969
Total stretch: .014

Specs for stretch guage:
.0110 to .0114

Funny it seems I got more stretch out of torquing???
I thought it was suppose to be the other way around. But, I'll take it.

Armando,

You went over your stretch by .0026 inches, I suspect your bolts may be damaged. Did all the bolts measure the same length before your torque, it seems unlikely because of the tolerances in machining each bolt. More stretch is no good, these bolts depend on the bounce back to hold under pressure.

Best of luck,

Alex

You screwed it alright. This is the type of engine that blows up, when racing.

So, what should I be doing now? I verified specs with ARP. I used the moly lube provided, I tighten and loosen twice to torque (49ft.lbs), then tighten a final time to torque(49ft.lbs). By-the-Book.
My torque wrench only shows increments of 2, so I set my wrench in-between 48 and 50. If I got closer to 50 would it make that much of a difference?
I used a "made-in-china" caliper guage and I tried to put it as square as possible. If I loosen again will I have to replace the nuts and/or bolts?

Armando,

To tell you the truth, I made the same mistake as you initially. I tried the torque method and didn't feel good about it so I removed every bolt and saved the proper nut to bolt fit. The difference between mine and yours was that I pre-measured accurately all my bolts and I had two that did hot bounce back after my last torque, instead they grew by about .0018 and .0022 inches after loosened up. I contacted ARP and explained what I had done and what I found with the two bolts, in the end I decided to replace those bolts and nuts. I have not started my second attempt yet because I'm awaiting new bearings but I'm convinced the only way to go is the stretch method. You and I most likely have way too much money and time into these engines to take that big of a risk.

I've learned that torque wrenches can be off by as much as ± 25% for cheap ones and less (± 5) for well maintained ones. In summary, there is too much doubt to suggest reusing your bolts and nuts....they’re screwed! You need to buy a new set of bolts and nuts then follow the stretch gauge method or go back to OEM and follow what ever procedure they recommend...probably stretch as well...not sure. The only possibility would have been if you had very accurrate measurements for each rod bolt before beggining, then you could have loosened them all up and re-measured them, if they grew any bit beyond what you pre-measured then their dead! I suspect with the cheaper calipers you used that there is too much doubt, you clearly do not know your baselines. Start over with new bolts/nuts and Stretch.

Best Regards,

Alex

I found this interesting article on their website about torquing:

http://www.arp-bolts.com/Tech/T1_InstallPages/T1_01_Retention3.html

In their installation sheet they require 3 cycles of tightening and loosening. But in this article it states the metals (rods and nuts) don't become consistent until 5 cycles. Since I followed the initial instructions I should cycle through the torquing 2 more times.

Also, in the initial instructions it states a torque spec of 49ft.lbs. But on their website it states 50ft.lbs. Which means my "approximate" torque of 48-50ft.lbs should be dead on. Since their seems to be dicrepency in their instructions and website, I don't think this is as an exact science as everyone makes it to be.

BTW: I might have gone cheap on the dials but my torque wrenches, and just about everything else I use regularly are the best, Snap-on. That being said, I will have my torque wrenches checked next time I see the Snap-on truck.