3 things I learned on my latest rebuild
 

Hi everyone,
I thought I'd share some things I learned the last few days. Nothing earth shattering, but perhaps it might be of interest to some of you.

ITEM 1) Rod bolt, torque vs rod stretch method:
These Raceware rod bolts had been torque 2 or 3 times before this time. I torque a couple using the recommended torque method and compared it to the rod bolt stretch. In both cases the rod bolt stretch was slightly below the recommended minimum of 0.011" to .015".

I tried making a rod bolt stretch gauge (RBSG) by modifying a C-clamp but I couldn't get repeatable readings. A "real" RBSG has a modified dial indicator with a stiff spring. (You can see my home made RBSG right behind the handle of the micrometer.)

http://forums.pelicanparts.com/uploa...1087520359.jpg


ITEM 2) My TDC mark was right on the money exactly:
After Jack ("snoman") shared his experience with pulley TDC notches that were way off (3 degrees ?) I made a mental note to check this on the next motor I did. The pulley notch on this '86 3.2 was right on the money.

http://forums.pelicanparts.com/uploa...1087520840.jpg


ITEM 3) It turns out that when measuring deck height, the piston has more than one degree freedom i.e. measuring two sides opposite each other doesn't give you the whole picture.
By deck height I mean the distance from the top outer edge of the piston to the top of the cylinder. I thought that if I measured the deck height along the axis of the wrist pin I would eliminate errors due to the piston rocking in the bore. In the case of my rods and JE pistons, my pistons had more "slop" along the axis of the wrist pin (the "stiff" direction) than they did at right angles to the wrist pin (the "floppy" direction).

Until now I didn't have an accurate way to measure this (just some digital calipers). I had a friend help me make a tool so I could measure deck height with a dial indicator and today I made some measurements. Measuring deck height at 12 and 6 o'clock on #1 piston yielded a .08mm difference which makes sense due to the piston rocking on the wrist pin. Measuring the deck height at 9 and 3 o'clock resulted in a difference of .25mm! This really surprised me. #4 piston was fairly similar (.07 & .18mm).

Please note: This test was performed on cylinder that had the base gaskets on them but were clamped down with cylinder hold downs as best as possible. This is one source of error.

http://forums.pelicanparts.com/uploa...1087522750.jpg

This was also the first time I've gotten porked by the crappy blue through bolt O-rings. Look for a separate post for that topic.

My Dad came down from Maine to visit for a couple of days and we gabbed a lot but had a good time assembling the bottom end of this motor.

-Chris

Here's a picture of the deck height tool I came up with. I took a depth gauge base and had a friend modify it to clear the head studs and piston dome.

http://forums.pelicanparts.com/uploa...1087523787.jpg

-Chris

Great post, Chris!

I just did my Raceware rod bolts as well, and was not able to achieve the specified stretch values either. After calling Raceware, they said measure the stretch on your way to 65 or 70 lbs torque. If you don't get the specified stretch, stop around 70 lbs torque. They said some have even been torqued to 85 lbs and they handle it fine. My bolts were new, and only achieved values in the .07 range.


JA

How 'bout some more detail on the failed C-clamp (G-clamp for the UK crowed). Why didn't it work?

Inconsistencies like these and pore thread quality on products like heads studs are what lead me to design and manufacture my own head studs.
As of yet, we don't have a source to manufacture rod bolts so we only use ARP or Porsche factory Titanium rod bolts.
There is no comparison between the quality of ARP vs Raceware. As a former dealer of Raceware products I couldn't believe the inconsistency of their product.
SUPERTEC head stud kits available through Pelican parts as are ARP rod bolts.

http://forums.pelicanparts.com/uploa...1087565399.jpg

In order for the stretch gauge to work, the dial indicator really needs a "suped up" tension spring so it will hold onto the rod bolt securely enough to support itself. Maybe I was drinking too much Mt Dew (a caffienated beverage) but I wasn't able to hold my home made stretch gauge on the bolt steady enough to get consistent readings.

If you've ever done the rod bolt stretch method with a micrometer (a PITA) you'd know why I spent a morning trying to make a rod bolt stretch gauge. :rolleyes:

http://forums.pelicanparts.com/uploa...1087565341.jpg http://forums.pelicanparts.com/uploa...1087565354.jpg http://forums.pelicanparts.com/uploa...1087565365.jpg

The ends of my rod bolts have little divots so I used pointy tips to make finding the center easier. This rod bolt isn't a Raceware but it has the divot I'm talking about.
http://forums.pelicanparts.com/uploa...1087565494.jpg

I hope you've enjoyed another episode of Bennet's Follies. Brought to you by the makers of Swepco blue pies and jams. :D
-Chris

That seems odd to me. It looks like it would work. My only suggestion would be getting rid of the pointy tip up top. Maybe a flat or a large rad?

Put it on ebay. "Porsche dilivar stretch checker - don't rebuild without one".

I want 10%. :)

I should have tried using it upside-down so it was "hanging" from the fixed end instead of relying on me holding it up against the bottom of the bolt. Both ends of the Raceware bolts have small divots so I used the points.
-Chris

Thanks Henry.
You are a just a treasure trove of info. I hope you will continue to put up with the guys who would give you grief over stuff so you can help the guys like me who really appreciate the experience you bring to the list.

-Chris

Chris, well said.

Jeff

Late Breaking News..
 

I checked the TDC notch on a 964 motor the other day and it was right on the money also.
-Chris

Nice looking work!

Thanks.
I must confess, it's a total Photshop job. I'm really an old lady with lots of cats and free time. :D
-Chris

Chris,

Most dial indicators aren't designed to be used upside down, so the approach of putting the fixed point on the higher end of the bolt and letting the gage dangle probably wouldn't be accurate. The dial indicator in the stretch gages is probably a special application type designed to be used upside down. I'll see if I can find the spring force of a few types, obviously I'd prefer to use a Millimess with an 8mm stem.

What angle on the points did you use? There are some 30 degree and some 60 degree floating around out there.

Was the mic helpful? Did you use points on the anvils or just the flat anvils of the mic?

After looking around there's no way to tell the increased gaging force necessary to hold the stretch gage in position. Somebody must have specified a bigger spring inside the indicator.

Here's the problem with that approach: if you spring-load the indicator point to keep it on the bolt, you are introducing hysteresis into the measurement, because as the bolt stretches, it has to push against the spring force of the indicator. I wonder what that does for the accuracy? Also it's a fundamental rule that you aren't supposed to side-load the indicator tip because it screws up the measurement.

There's a better way. . .

Hi John,
Eating my lunch on the road so just a few quick thoughts:
- While the greater strength spring would decrease the stretch slightly, since we are dealing in the neighborhood of many pounds of force to the stretch the bolt, a few ounces of spring pressure shouldn't matter.
- The digital/electronic dial indicator probably does not care what the orientation of the encoder is.
- I used a micrometer with flat anvils. It's measurements were repeatable.
- I tried a "coil-over" approach to increasing the spring tension. I used an extension on the dial indicator and a coil spring over it. To trap the spring, at the tip end of the extension I put a washer and then screwed on the point.
-Chris

Is a standard C-clamp body strong enough to not deflect? Or maybe I should ask if the stretch gauge bodies are any stiffer. I'm going to be getting a stretch gauge from Summit for my upcoming rebuild.

Ed, I can put the ARP stretch gauge in the same box if you want....

Cheers

Jeff: I'll be a month or two away from needing that one yet...

John, I admire your desire to find the best way to do things, you think like I do in some things. Not sure if that is a good or bad thing?!? :)

But, as far as rod bolts go, I would be more inclined to find out from ARP or Raceware what the failure rate is when folks use the ARP gauge (like I do). If the failure rate is acceptable (not sure what value is acceptable to you or me) then I would trust they took some of your concerns into account when they decided on a stretch spec.

However, if the failure rate is unacceptable, then by all means try to find a better way to measure.

I guess I am saying that if they (ARP) test their product with their own gauge and the spec is based off of that testing, we may be better off using their tools and spec than comming up with our own.

Of course I am only thinking out loud and have had a glass (OK 2) of wine!

Cheers

Jeff, I hear you, but remember that rod bolts were installed for years using a beam-style torque wrench, lubricant and a guess. Then came the angle torque method, a more sophisticated guess. So suppose you're ARP, you're thinking, "anything we can do to enhance the ability to get a repeatable stretch will lower the failure rate of our bolts, enhancing customer satisfaction AND we get to sell a $10 chinese-made dial indicator and an anodized aluminum frame for $150!"

If I'm going to the trouble to engineer my own gage, I'm going to try to avoid some of the known pitfalls of the ones on the market. Such as, making the frame out of aluminum, which bends and expands a lot when heated.

It's all theoretical of course. . . :)

Makes sense, can't really argue with that!

Cheers

I wish I had pictures of the measuring devices we used to tighten the cable bands on some of the big suspension bridges (GW, Verrazano, Williamsburg, Throgs Neck, Whitestone)

In reality they are just larger versions of the bolt stretch gauges used to verify rod bolt elongation..

If I may just step in and smack you guys upside the head!!

I think you are making mountains out of mole hills...

Tim, I will drive across the GWB in complete confidence knowing that it was you who tightened the cable bands. :)

Of COURSE it's overkill, that's what makes it a fun exercise. Then again, trying to design a tool that's cheaper and more accurate than the commercial alternatives is the essence of the Pelican DIY spirit.