Thrown Rod at Daytona

[longhornchris04]

Originally Posted by 911 tweaks

wow... and wow again... especially if we are to now think to NOT down shift to aid in braking... I recall how most of the porsche race movies they down shift... maybe the key is that they are 100% race motors and only need to last the 1 race...
Great info here & thanks for sharing!
Bob

That, and I bet if you had telemetry on the car it would indicate that the driver heel-toed the downshift and was hard on the brakes the entire time... i.e. never used the engine to assist in the braking, just downshifted to ensure they were in the power band once they got back onto the gas.

Note to self, add ARP rod bolts to the eventual rebuild budget... or better rods & rod bolts. 1 more step down the slippery slope, but if I'm going to do it right then I'm going to do it right.

[lindy 911]

I was on another thread last night that addressed stretch bolt tightening. If you used a torque wrench and not a form of stretch measurement, couldn't you trace this failure back to that? The thread said that even when the nuts were torqued to spec the bolts were not at their proper stretch. It sometimes took far greater torque to get the bolts to their proper stretch measurement.

I read with interest as I am in the middle of a 3.2 SS build. I know from years of motor cycle racing, which use a similar two-piece case clamped crank assembly, that the bottom end is king. Looking forward to your re-build thread.

Lindy

[jgparker]

Hi Lindy,

I did the Wayne Dempsey Rod bolt torque procedure to the letter, so the rod bolt torques can't be too far off.

The interesting thing was Kevin Jeannette (935 and 962 engine king at Gunnar Racing) said forget all other methods. Torque all the nuts to 10lbs then 20lbs then 30 lbs and finally to 40 lbs. He's built hundreds of racing engines, including Sebring and Daytona winners, so he might know what he's talking about. He probably was talking about ARP or Titanium rods though.

Check out this engine shop. The room had more titanium than an SR71.









All photo's from Gunnar Racing secrete location in Florida.

Thanks,

JP
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[Walt Fricke]

No doubt there are many ways to skin the rod bolt torque cat. No doubt Jeanette uses a lubricant he trusts when torquing. Pauter doesn't give a stretch figure with their rods (which come with bolts), though they have one if you ask for it. And I've not seen a stretch figure for factory bolts. And then there is the angle method. All ways to achieve the clamping force that a certain amount of bolt stretch gives.

But the bolt stretch method is not really difficult, and the tool for measuring is not expensive. Plus, with these good aftermarket bolts, you can remeasure at rebuild time and may be able to reuse the bolts - which is no small cost savings.

Neat photos.

Walt

[lindy 911]

Changing from rod bolts to chain tensioners, I notice that both of the engines in the first picture do not have oil lines to the tensioners. Are they running a mechanical tensioner? If so, what type? I see in Pelicans catalog that these are available and cheap, a lot less than the oil fed pressure units. Again, coming from motorcycles, adjusting cam chains is part of life. Am I missing something? Also, the engine on the left in the first pic looks a lot like whats sitting on my stand although I'm sure it's quite different inside.

Lindy

[304065]

My guess is that they are solid tensioners-- but these are unsuitable for anything other than race engines.

[kenikh]

FWIW, I strongly believe that the most reliable solutions are the 930 tensioners w/ safety collars.

[lindy 911]

OK, I understand the fix it an forget it mentality. Why would the solid tensioners be suitable for racing only? Is it that you would have to add cam chain adjustment to the maintenance to-do list? The chain box cover gaskets are cheap and the time needed to pull the covers and adjust the chains seems minimal. Seems to me this is by far the safest way to keep your valves out of the piston tops. Maybe that's why race motors use it?

Lindy

[Walt Fricke]

I noticed the lack of extra tensioner plumbing also.

I'm with Kenik on this one.

And these may be engines built to be period correct. The Carrera tensioners came in with the '84s, and they may well be older engines.

Walt

[smokintr6]

From the pictures above, what is the 4 cam engine with what looks like watercooled heads, and air cooled jugs? I would have instinctively guessed 959, because the parts look very "production-esque"... but I looked at some pictures, and the offset alternator doesn't quite fit in. Is it from a 962?? I'm going to go out on a limb and say that might be the most expensive, or at least rare unit in the room.

And as far as mechanical tensioners go...I think most people's heads woul explode if they had to worry about a service like that. On a race engine with a 50 hour top end, I would imagine the chain adjusting service interval takes care of itselft from simply taking them apart and reinstalling. I don't have first hand experience with them, but I can't imagine that the chains stretch very rapidly. Would be interested to hear from someone who is actually using them.

[lindy 911]

I understand the "period correct" thing but if that were so, the chain box covers would not have an oil passage that's been plugged. I like the idea of mechanical adjusters; too many things can go wrong with anything automatic like pressure fed adjusters. Does anyone have any first hand experience with the mechanical adjusters and can you add your two cents please? The pressure fed kit is up to $750 now. That's pretty pricey for what seems to be non issue.

I know that if you're going to just drive your car and not pay that much attention to things, sure the pressure fed stuff look like a good way to go. My case is very much different as I like to monkey with the car as much as drive it.... sad but true.

Lindy

[flat6pilot]

What motor above has the alt on the side like that?

[JFairman]

Kevin is a very busy guy but he usually replies to emails in the very early morning.

I'd email questions about what rod bolts he uses and stuff like that.

When I worked there he used all origonal factory porche racing parts and I saw plenty of gorgeous mirror polished titanium factory rods from 935's and 962's when he was building those engines. I think those were Pankel rods.

I think I remember reading he used Pauter rods in the Rat motor on his website.

His facility is a totally amazing Porsche place... The pic on the top of his homepage is a view in the seperate museum building.
Gunnar Racing
A very cool place to be in S. Florida in many ways, and it feels like they keep it in the upper 60's in there to help preserve the cars and tires.

[ninesixfour]

Originally Posted by jgparker

This is the way I'll remember it, as a great fun and fast engine that never let me down until then end, rather than the pile of scrap now in my workshop. JP

How many hours/miles did you get out of it?

[jgparker]

I don't remember seeing a single set of pressure fed chain tenstioners at Gunnar. Kevin is not a big fan of them. He told a long story about them destroying a bunch of race engines before the factory figured out they were causing problems. It has nothing to do with looking period correct. He said he's thrown away a pile of them. The ones I saw had turbo tensioners, not the solid ones. There is a set in one of the pictures above.

If I remember right, that funny looking water cooled engine is for a 962, and yes, its worth more than my house.

I got about 50 hours and 6 years out of my engine before it let go.

JP
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[lindy 911]

What are Turbo tensioners? Evidently, they are not pressure fed. How would I source these?

Lindy

[Steve@Rennsport]

Turbo tensioners are term used to describe the last version of non-pressurized chain tensioners used from 1978-onward.

Provided they are installed with the wide idlers and tensioner guards, they are OK to use. I strongly recommend the pressurized ones for street cars, though as they are very reliable,...

[jgparker]

I do want to clarify one thing, my cars all have pressure fed Carrera tensioners. For a street car, they are probably the most reliable solution. Racing is probably a different story.

JP
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[lindy 911]

So if I have a '78 SC I have "Turbo" tensioners?

Lindy

[Steve@Rennsport]

Originally Posted by lindy 911

So if I have a '78 SC I have "Turbo" tensioners?

Lindy

Thats what those cars came with from the Factory.

The Carrera pressurized ones can be ID'ed by the small oil line running down across the cam chain covers.