2-pc case PR tube sizes?

[Ron LaDow]

Got a question as to whether the Pre Mat PR tubes will fit a 2-pc case. I have no idea; are PR tubes interchangeable between 2-pc and 3-pc engines?

[Erik Thomas]

Ron:

I asked Jim at KTR motorsports to take a look and advise. He has some of your tubes on hand, and an early engine that is apart to check. We shall see what he says. I want to use your tubes, if possible. I also want to use the Porsche pattern tubes, which help keep oil from flowing up in the heads when cornering.

[Ron LaDow]

Erik,
AFAIK, the tubes with the extended case ends were developed (welded up) By Richie Lukes at Lukes & Shorman; the go-to Porsche service and machine shop in the Bay area when I was but a yute.
Yes, the Pre Mat parts have that feature.

[Harlan Halsey]

The 2 piece case is a 36 HP VW case and the Porsche pushrod tubes were originally 36 HP VW even in the 3 piece case engines. It is local lore that Lukes and Shoreman extended the pushrod tubes into the case by silver soldering or braising straight section on to the inner end. They did this because the racing cars which they were preparing were loosing oil out the rocker covers on the track. That idea was picked up by Porsche and late Porsche source tubes incorporate the change. On a street car the value of the change is questionable, but it may keep some oil out of the valve guides if they are loose.

[Michael Foster]

And the longer tubes allowed Lukes and Shorman as well as Porsche to get rid of that funky super90 slide valve piece that would sometimes stick and not work.

Michael Foster

[Erik Thomas]

IMAG0033.jpg (87.28 KiB) Viewed 1159 times

Here is the report : yes they do work just fine, here is a picture of the early ( 36 HP VW /early Porsche case with Okrasa heads.

[Ron LaDow]

Erik, those springs are over-loaded and will soon ruin the seals. How about a photo of the tubes in the rocker box? It's an easy mod to shorten the (tumbled) sleeve, and perhaps the tube itself. Still hoping for some real dims...

[Alan Hall]

Ron, I wish I could 100% answer your question, but I 'm not sure. I believe 36hp VW tubes are slightly shorter than 356 3-pc case tubes, but I am not sure if a 2-pc case Porsche used the same tube as a 36hp VW. As I recall the 36hp tubes can be used on a 2-pc case 356, but it could be that they work by stretching the tube slightly. I looked through my box of tubes and I have some non-extended tubes that matched the extended tube length but I don't know if they are from a 2-pc case motor or an early 3-pc case motor before they went to the extended tubes. Photo attached w/ the 36hp tube noticeably shorter. Of course on top of all this is that some or all of theses tubes may be aftermarket, which might have a slightly different length.

Added by edit: I just remembered that I had a set of tubes with a disassembled '54 2-pc case motor. Checking them they match the 3-pc case length, so it appears that your tubes would work on a 2-pc case 356 motor but probably not on a 36hp VW engine.

[Ron LaDow]

Erik,
Here's how much the springs should be compressed:

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If you have access to a lathe, I'd suggest you shorten the rocker-end of the tubes and the tumbled sleeves by ~3/16" just to let those seals last a while.
But if they do go, we know you won't have to pull the heads to change them...

[Al Zim]

In your shop manual for the 356A page E39 section 20E is the factory description on how to adjust the 36 HP VW push rods when you are rebuilding an engine. It is very important for you to have this book wen you are working on you 356. The picture of 36 HP VW push rod tube is shorter since it has been used. I prefer to use a small screwdriver that has a handle that fits into the end of the tube then you can easily manipulate the tube without causing any damage. Stainless tubes are not as ductile as the factory push rod tubes were. Because they are "new" I have never adjusted them. It was posted that you want the oil to flow to the valve covers. That was never the case. The long bottom ends of the tubes precluded this as did the pushrods with wooden dowels in them. Later the factory removed the oil squirters on the later rocker arm assemblies to further alleviate oil burning situations. al zim 2018/03/11

[Erik Thomas]

All:

Thanks for the info. I have passed it along. We have the ability to shorten Pre Mat tubes as needed, nice to have that option.