Rod bolt creep

[oneblueyedog]

I followed the precise process in Wayne's book for assembling the crank and rods. It went exceedingly well except for a doubt I have about rod number 5. I used the 90° tourque method. I looked at all of the rod caps and one of number 5 bolts tangs twisted over the notch that stops the tang of the rod bolt. I thought that I wasn't careful in its installation. I removed it (Red threadloker really holds after 30 min). I went out and bought new nuts and bolts and re did #5. So after the torque the second time- it twisted around the same way-more so. The opposite tang is protruding out in the wind. When I removed the rod after the first installation, the tang scraped the other side and left a burr. I smoothed it off to not having risk a chip fleck off in the case. So I now have a lighter rod adjacent a heavier one 677g-678g ( but postage scale accuracy so I'm not taking it too seriously).

Rods rebuilt by Competition engineering.
Steps on the rod cap were evident. Less so after the creep over it.
Bolts and nuts installed clean and dry with red threadlocker one rod at a time.
20nm initial torque-90° final set.
Installed rods fall essentially the same speed- slow and steady glide down.

I compared the new rod bolt to the old ones and the step below the tang and head is a bit higher. This might be why it rode over the step in the cap.

So the "Swiss watch" factor is out of my rebuild.

What can I expect and get away with?

I wanted to seal the case up today but I won't until I hear a few opinions.

Thanks for any help.

[afterburn 549]

I am thinkin that a care full rod inspection is due in the boss aera there and maybe the i.d.?? ...dose the bolt fit into that one like the others??

[davidl]

Hello there.

I'd be very very suspicious too.

This suggests to me that the bolt was not fully seated against the cap before it was tightened.

So, I'd start right from the very very basics.. I would strip this rod again, check the following, just to start..:

The bore size in the rod.

The bore in the cap.

Any burring in these bores.

The underhead diameter of the bolts.
(I have seen bolts which were actually tapered!).. NOT Porsche ones!
The underhead radius of the bolts.

The radius of the cap bore where the head has to seat down.

My guess.. wrong bolts or wrongly machined cap.

And, if I found this fault on one , I'd assume all are the same..

Sorry, but this is an excellent illustration of why it is good to do your own engine, ...

Kind regards
David

[oneblueyedog]

Thanks for the suggestions.

Oddly, the bolts came from Porsche and the cap was not re-machined on the end. I guess the initial factory step machining was not deep enough to capture the pips on the end of the bolt. I re-compared the bolts old and new. They are identical execept for the thickness of the triangular pip on either side. The new bolts are thinner. Old are .08"
new are .06". Measured at tthe tip of the pip. Each have Verbus 129 stamped on top.

Bentley and Wayne say the 20nm/90° method with Wayne suggesting threadlocker.
Bruce A's book says a range 37-40.5 ft.lbs. with moly lube and motor oil.

I once had a technical spec manual but it's disappeared. It was a 78 911sc (what I own).
Anyone know what the tech book said? It's out of print.

I'm going to go to the Fisch. The reader is up in the attic.

I talked to a very experienced mechanic and he said I was ok in every respect. But the accuracy here isn't Swiss. It's German and that's fine by me!

BTW. The stretch between the 2 bolts old and new removed. Take into account the old ones had been torqued twice- one for assembly and another for resizing the big end.
Old-2.483" torqued twice-no threadlocker
New-2.494 torqued once- w/ threadlocker

I wonder what they are untorqued?

I blame it on the pips!

Lee 78sc

[snowman]

The critical dimension on the rod bolts is the diameter. It should be within a thousandth of an inch near the top of the bolt. The middle may be thinner due to streching. The bolts must fit snug to very very snug, not loose in the caps and rods. If they do not they may be the wrong ones or some of the bad ones floating around out there. IF you got them from a repudable dealer they should be ok, otherwise be wary.

The bolts need to be tapped into place with a small hammer before tightening. This will help seat the heads and prevent twisting like you have experienced.

The nuts MUST have lubrication. The factory shop manuel, the bolt industry, and I, all dissagree with Wayne here. You cannot have both loctite AND lubrication as they are mutually exclusive. A properly tightened bolt is held by its spring tension and consequently NO thread locker is needed. Thoroughly oil the nut, bolt and mounting surfaces, torque and then turn 90 degrees. DO NOT USE THE 37 to 40 Foot lb torque spec as it is highly inaccurate compared to the torque and angle method. BUT remember stretch bolts are SINGLE USE ie single tightening devices.

Torque to yield bolts (the kind you are using) are extreemly reliable and will not loosten unless the bolt is stretched even more than when you installed it. IF it does this you have FAR exceeded the RED LINE of the engine and no loctite will save it.

Race wear makes very expensive, but reuseable, rod bolts for this application. This is an alternative and can inprove the chances of the engine surviving if over revved by a significant margin. If you are building a race engine I would strongly recommend them, if not, the factory bolts are fine. SPS makes the ultimate bolts, but at $25 each and up they are only for real race engines.

Stretch is measured while the bolt is being tightened. A special dial indicator is clamped around the bolt, end to end, and the length monitored while the bolt is tightened. The initial length is noted and then the bolt tightened to the point it is say 0.006 thousands longer. This is typical for a Raceware or SPS bolt. This kind of spec does not apply to a stretch bolt. A stretch bolt is tightened to its yield point and beyond. Thats the point where the bolt takes a permanent change in length. It guarentees that the bolt is as tight as it possibly can be, but at the expense of ruining the bolt for further uses.

[oneblueyedog]

Thanks to all of you. Have a prosperous and healthy new year. Next engine I rebuild I'm using motor oil on the bolts&nuts, if the powerplant uses it.

Yes indeed I had to tap in each of these bolts in with a plastic faced hammer. Number five was the only oddball. The shallow step and the thinner pips caused the trouble. This engine will never see over the rev limiter. Hope it lasts another 217k.

Thanks for the explanation about yeild bolts as opposed to stretch. I thought it was fun to see if they really did yeild since I bought a dial caliper. That instrument is sweet.

Happy new year.

[davidl]

Hello again.

It seems very unlikely that the tiny differnce in the little protrusions on the cap are enough to explain this..

If the bolt tang is hard up to the face of the cap perch, there is no way at all it can come away from this once the nut is run on..so it simply cannot turn even if the little protrusion is a bit low..

Unless the bolt is made wrongly with the tang off the face, or the bolt is not seating on the cap perch snugly..
Is there a chamfer/radius on the cap bore entry sufficient to clear completely the underhead radius on the bolts you have?

Or maybe you were relying on the nut to pull the bolt in fully, rather than seating it with a few smacks first?

Kind regards
David

[jgparker]

Jack,

Are you saying you can't use the stretch measurement method to torque Porsche OEM rod bolts? I guess that explains why I can't find the stretch spec for anything but the Raceware and ARP bolts. I would prefer to use this approach, since it should produce the most accurate torque.

Thanks,

JP

[oneblueyedog]

David

The bolt's tangs are not squarely against the bottom of the perch.

Lesson here is- Check these new bolts! Check how they fit in the cap.

I r&r'd this rod 2 times. I had the same doubt as you did about the installation.

I tested the nuts on the rod for torque with a click torque wrench at 40 ft pounds. It didn't move and clicked. It's either torqued over this checking torque spec or it's the glue.

I'm cool with it.

I'll send you the comparison bolts if you want 'em. It's quite interesting.

Thanks for your help.

Best regards,

Lee

[ChrisBennet]

Thanks for sharing what you found. Good to know.

I personally wouldn't trust a clicker type wrench for rod bolts. They are one of the most critical fasteners in a motor and a clicker type torque wrench is one of the least accurate types of torque wrenches.
-Chris

[oneblueyedog]

I'll check it with the bar scale wrench then. Thanks

Lee

[Wayne 962]

[i]The nuts MUST have lubrication. The factory shop manuel, the bolt industry, and I, all dissagree with Wayne here. You cannot have both loctite AND lubrication as they are mutually exclusive. A properly tightened bolt is held by its spring tension and consequently NO thread locker is needed. [/B]

I based my recommendation on the lessons learned from the many Engine Rebuilding experts that I spoke with in preparation for writing this book. I did not pull this recommendation out of thin air. There are people who agree, and obviously some who disagree. Here is my reasoning behind this recommendation:

Rod bolts on the early cars almost never fall off, and are generally not a problem area of the engine. I have not heard of any early engines with rod bolt problems, either from failure or poor assembly, or the reusing of rod bolts. On the later cars though, the rod bolts can stretch. This makes the nut come loose, and potentially fall off, as you no longer have tension holding it in. I recommend the red Loctite based on this failure mode (not described in factory manuals, or the bolt industry), of which I offer proof on page 82. As a measure of precaution, I also recommend this method for the early cars as well.

There was a 3-4 page debate on this issue in this forum a few months ago, where these arguments were all hased out.

-Wayne

[oneblueyedog]

Wayne,

Thanks. I appreciate the forum you sponsor. I'm sticking with the book you wrote. It's not coming apart now and probably never will unless someone applies a torch to the nuts to melt the threadlocker.

If it ever gets rebuilt again, it will need a new crank and rods anyway at 400k+.

Cheers!

[snowman]

TOrque to yield bolts are not worse than the ones that are tightened to a certain stretch, they are just differen't. They are made to use one time, while the others usually are not. I kind of think that they are better in that you are guarenteed the max holding power available for the price. Any bolt tightened to its yield point will be holding as much as it possibly can. THe proceedure for tightening is foolproof, if followed, in other words in ALL cases the bolt is holding what it is designed to do. With just torque you can be off as much as 100% or more in either direcition. With stretch you may be more accurate, but you are also using a more expensive bolt to get the same results as a torque to yield bolt. If you spend even more you can get much more holding power, but the bucks really add up at $25 up per bolt.

I think the numbers are approx as follows:

stretch to yield bolt 180,000 to 220,000 lbs and inexpensive (relatively of course)

Raceware 220,000 lbs plus but reuseable (expensive)

SPS 300,000 lbs or more and reuseable. (VERY expensive and special EXTREEMLY expensive rods may also me needed to use them).

If bolts are giving out they are over stressed, ie to small to do the job. Please contact Carillo or other similar mfgs to find out the details first hand.

An observation- race car engines, almost NEVER break anymore. Almost ALL race cars use none other than Carillo rods, which also use SPS bolts.

If you are spendiing bo koo bucks building an engine, and save say 200 or 400 bucks using some rods other than Carillo, WHY??? Out of the $10k on up you are spending why risk EVERYTHING for a couple of hundred bucks??? I have personally seen people spend upwards of $25K on an engine and save $100 by using an off brand rod and ARP bolts, Note: Carillo rods are NOT a couple of hundred bucks, thats the DIFFERENCE in price between the Carillo and other, lesser rods. WHY WHY WHY? Just an observation.

NOte: All good rods are extreemly expensive, the also rans are only a couple of hundred less than the real thing. The others... well stick to the stock Porsche rods, they are better.

VARA race cars that have been running for several years mostly use Carillo rods, at least I have not met, even one, of the members that, after a couple seasons, that does not use them. Are there any VARA members NOT using Carillo rods out there??? IF there are they are most likely using stock Porsche rods, they are the ONLY other rod that stands up to racing.

[Wayne 962]

Originally posted by snowman
Any bolt tightened to its yield point will be holding as much as it possibly can.

A little clarity here. Any bolt tightened to the level just preceeding it's yield will be holding at the maximum torque level. The theory behind this is that once the bolt starts to yield, the tension (by definition) has to decrease. Thus, the maximum amount of holding power on the bolt would be present when the bolt is still under elastic deformation - not plastic deformation. Now, different materials may have different elastic / plastic curves, but once deformation begins, in general, the metal is typically not holding as much tension as when it previously was not deformed.

Carillo rods are good and nice, but an unnecessary expense in a street engine. The ARP / RaceWare rod bolts are a more than adequate fix for the rod bolt problem. The solution doesn't need to be over-engineered.

-Wayne

[snowman]

Wayne,
Sorry for the slight oversimplification, you are 100% correct. Those darn stretch bolts are so good in the field I would rather rely on they than the torque of any fastener. Thats for any street use, period. The little you give up is well worth the confidence it is tight.

[davidl]

Hello again, oneblueeyedog.

If the tangs are not hard up to the rod bolt perch, you may have a serious problem.

The issue is not what torque /angle value was achieved.

The concern is with the underhead radius of the bolt, or the diameter of the bolt, or the shape of the grip surface of the bolt head, or the shape of the cap perch.

There is some reason why the tangs are not hard up, and you need to know what it is...

My guess, the factory may not have put enough chamfer on the bolt entry to clear the underhead radius..

This will lead to accelerated fatigue, and although the engine lived with this, ( presumably) when originally built, you do not want to risk it on a fresh build..

This sort of detailed attention is what you gain doing it yourself, unless you are prepared to pay for the experirence and knowledge, and reputation of one of the Professionals who frequent this forum...when you can count on this...

Kind regards
David

[oneblueyedog]

The bolts are stopped against the end cap.
They have carved into the end cap and created their own new stop.
The nuts are torqued over the checking specification. (because of the 90°, 3.2 litre tourque suggestion?)
I did not assemble the rods poorly.
The bolts were factory suppiled.
The engine was factory supplied.
I have no control over manufacturing variances Porsche makes.

I guess I had a few choices on how to torque these nuts. I chose the most modern choice.

I asked an experienced builder about this subject too and he said "wait a minute, that's the torque spec for 3.2 litres. He said I'd be fine after I asked him if the bolts would fail over torqued like this.

I'm in limbo now. And what really pisses me off is that the rods get destroyed taking off the fasteners(I'll try heat).

So I can take them off and buy new rods or used rods and have them all reconditioned again.

Only one participant in the thread has a stand on if I'm ok or not. He has doubts, which is the safe way out. The picure is obviously showing a problem. It looks like a hack overtorqued the fastener.

Thus spend more money as a penalty for bad assembly, rod bolts out of spec, radii, Porsche's sloppy manufacturing standards,superceeded tourque specs. One can make many opinions and assumptions with this thread. I have mine now.

I'm going to drop by Boardwalk Porshe next week and see what they say about it all since they have a nice relationship with PCA members.

My question now is this- is the 90° torque method the torque method Porsche uses for 3.0 liter 911SC?

Page 82? Looks like the bolt stretched and snapped. What's holding the nut on the stub? The photo makes a graphic point of not over revving a 3.2 and buying Raceware which the photo clearly goes with the paragraph-Rod Bolts.

I'd expect something like that also happening via a re-use of rod bolts or an over-torque. Which is giving me more reason to tear it down and do it over. I'm glad I have piece of mind that the Locktite will keep the nut firmly glued to the broken bolt if they ever go to Valhalla.

I followed the book. The bolts crept around. They screwed up my rods.

Anyone got a set of used rods for sale? What's your price? Rods and Crank? I'd be interested in that too.

So my answer to all of this is- Check the bolts. Check the fit of them into the cap. Use the torque method specified for your engine.

The remedy if anything is wrong? I guess there is no answer for a street engine, unless you toss the Porsche bolts and rods and go with racer stuff. I'd like to do that someday, not now. Maybe the Raceware.

This isn't very fun BTW. I never thought such a precision engine could be so cloudy in the way it goes together.

Later.

[Wayne 962]

Okay, there is something wrong here. First of all, I have never heard of this happening. Second of all, the tangs on the ends of the bolts are not designed to have any great amount of torque applied to them - even if the tangs weren't there, theoretically, the bolt should not turn in the bore - the friction between the end of the bolt and the end of the rod cap should be enough to hold the bolt steady (in my opinion).

On Page 82, I believe that the nut on the other side of the rod fell off, making this one snap.

The 1982-83 Porsche spec book lists the angel torque method as used on the late 911SC rod bolts, which are the same as the early bolts from 1972). The even earlier bolts are similar to these bolts as well. There may have been a Porsche tech bulletin superceding this method for the early cars - I can't recall off the top of my head.

You also can't compare new rod bolts to ones that have been run in a car - they are going to be different lengths, and you also have to measure the starting stretch to compensate for manufacturing tolerances as well (not all the bolts will be the same lenght when new).

I think I would need to see more pictures of the tangs before I would recommend a solution to you.

-Wayne

[oneblueyedog]