SCAT Crank issue

[Glen Getchell]

I was talking with a long time (40 years) respected 356 racer & Porsche shop owner a few days ago, and he was indicating that there is an issue (and always have been) with the way SCAT machined their cranks around the #2 bearing which makes a strong crank, but causes a incorrect end play resulting in hammering of the case.

I just put together a new engine which I shortly there after all but ruined with a missed shift (something I am currently to pissed off about to discuss). However, the crank for that engine is a SCAT that was used in my previous engine. So it has been in use for about 15 years. Now ironically I was not able to re-use the old case because the areas that hold the bearings on two different bearings were were chipped out. That would not have been from the last failure which was top end issues, but I thought it could have been from breaking the crank years ago (hence the SCAT Crank). At that time I did not build the engine myself, so I never saw if there was any damage to the case. And that mechanic turned out to be a hack.

Anyway, I have never heard of this problem. And while I really do not want to open the bottom end up again. It's all but in parts again now, and I'd like to hear from others on this SCAT crank issue. Because this is the first time I have ever heard about it.

Glen
64Cx2

[Eric Wills]

...

[Olivier Auvray]

Scat cranks have a rather large radius on the journals. I have had success with a LIGHT cut on the edge of the #2 main bearings. Only recommended if you have alu bearing shells. I wouldn't try this using steel backed bearings.

???

The Scat crank is similar to a SC/912 crank with 55 mm bearings for number 2 & 3 that are exclusively fitted with steel backed bearings.
With proper tool, you can cut steel backed bearing............. In any case it's mandatory If you use a Scat crank!

[Eric Wills]

...

[Vic Skirmants]

Chamfering the bearing material with a bearing scraper is easy enough to do; you're not cutting any steel.
Glen, the SCAT cranks have always had a larger radius for strength, hence the need to radius the bearings. This has been known since the beginning of SCAT crank availability. You need better tutors.

[John Brooks]

Vic.

First I have heard of this. I was getting ready to start one tomorrow, with a scat crank and carello rods. I have never used a scat crank in a 356. What is the size of the radius on the crank? The case and parts are down at Toms house and I won't see it until tomorrow. Do you have to scrape a radius on all the berings or just the center two. I have some machining capability so I can make a radius cutter tool, it's just the main journal radius correct? Are the Rods OK or do they need relieving also?

Your thoughts and suggestions please. I am on the TAN if you would care to call.

[Vic Skirmants]

John; only the #2 bearing needs the clearance, and only on one side. When pre-fitting the crank in the case, it is obvious what needs to be done.
Not a big deal, but it is important.

[John Brooks]

Vic. Thanks, I have had a brain cramp all day worrying about this.

[Ron LaDow]

I know the thread refers to SCAT cranks specifically, but given the age of the parts involved, most any crank/bearing fitting needs a close look by now.

[Glen Getchell]

Can somebody describe precisely what has to be done to correct this issue? Maybe even some photos, as I am not understanding the fix? I'm more of a visual person. It may be obvious when I look at it, but I would like to know before I open the engine it up again

As I said I have never heard of this even if it was well known to others (SCAT certainly doesn't tell you). When this crank was put in originally, I did not do my own engine work. One would think that when you pay $2,000 for a crank (in early 2000's money) that no modifications would be needed. I know that is a silly belief, but really, parts should freaking fit! Especially expensive ones.

I doubt the previous mechanic knew anything about this either. I know he never mentioned it. But then there is a reason I have learned to do my own work. I have found I can screw up my cars faster and cheaper than the local shops.

So it looks like the bottom end is coming apart again. Maybe the missed shift was a blessing. Hmm, sure doesn't feel that way! Again photos, drawings, or what to Google etc... to explain this fix would be appreciated. A Youtube video would be gold. I'd be surprised if I'm the only one not getting it, but at this point I have no pride. So I'll be the one to open his mouth and ask the "stupid" question. Thanks!

Glen
64Cx2
P.S. I am running all aluminum AA main bearings.

[John Brooks]

Glen

I will try to post some photos tomorrow as I assemble Toms engine. If it is what I think it's should be no problem.

[Paul Lima]

Paul Christensen covered this subject in some detail in the Registry vol 35, number 6. I've attached his article here

[John Brooks]

What fun for us old guys. My first engine in years, but the P-Tools still fit. YEP it has a radius and clearance is required. A 5/64" (1.9844mm) radius on both sides of the #2 bearing. It migh be 2mm, I can't find a metric radius gauge. I did not get to the rest today.

The scat crank is well balanced and I like it. Measured the #2 side clearance at 02.83mm so I probably need to relieve both sides.

But the new pistons, wrist pins and rods all weighed is the same. I need to read up on weak wrist pins these are 111.9 grams. These are all way lighter than the past engines I did using factory parts. The new rods use bolt stretch to measure torque so an open end wrench is needed to get around the dial indicator tool on the bolt. Looks like an evening of YouTube on the new design stuff.

Just saw the article link, exactly what I needed.

This is not my engine, it's Tom Olsen's. He drives his car 6-10,000 miles each year. Many may know him from the PCA events, he used to drive from Anchorage, Ak to the parade every year. Probably has more distance trophys than anyone. I need to be sure on this build is correct.

[John Clarke]

Paul Lima Thanks for finding and sharing Paul's really useful Article.
Is it the larger radius on the Scat Crank that makes them so strong?
Jay

[Vic Skirmants]

John; you only need to relieve one side of the bearing.
I remember most stock early pistons as having pins around 103 grams, so I think yours are plenty chunky enough.