Boring out Porsche Birals

[Alstrup]

Hello.

Some time ago I read somewhere that one of the hardcore 30 hp tuners were boring out 82,5 mm Porsche Birals, and the person went through the metal core. Was that tryinng to go to 83 mm or say 85,5 or so ?
I have been looking at a set and dont really see a problem going 83 mm. But I would like to hear opinions before I begin working on them.

Thanks

Torben

[Mr. Motorhead]

I have a set of those (birals) that I picked up a while back with some other parts. They are bored for 83mm, I'll be using some German big bore 40hp pistons in them. I don't know what the application was that they came from, but the barrels fit the 36hp stud pattern perfect, no extra work needed. These were opened up to 83mm using an adjustable cylinder hone like you see used on a V8. There is plenty of meat left on the barrel when they were done.
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[Alstrup]

OK. That´s what I thought.

With 10 mm studs I find it a bit tight, but converted to 8 mm studs its fine.

Off to work

T

[Beetspeed]

Is it is a good idea to bore out a liner that was deemed critical to begin with?
Even less have had good luck with tuned engines (= even higher strung then stock) and birals, so boring them for a tuned engine...I dunno...
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[Alstrup]

Walther. The problems people typically encountered with the Porsche Birals were when they really put the pressure on, - such as oil blowby and the likes. As long as these engines were kept stock or mild there "wasnt" a problem.
On a 30 hp engine where the power per cylinder will be about what a SC engine produces I do not think there will be a problem. I am going to try it out now and see how they behave. If worst comes to worst and I am proven wrong, I will have to modify a set of 83 mm 40 hp cylinders and replace the Birals with those.

(About 10 yoears ago I built an engine out of customer supplied parts. The cylinders were old NPR Biral 92 mm. That engine pulls a modest 110 hp. But it runs nice and way cooler than a typical thin wall 1835 all day long. It does have the typical oil cloud on start ups after shutdown on really warm motor. Other than that it still behaves nice)

T

[bvilletom]

The Biral 912 cylinders have a bad reputation in the Porsche world because the iron cylinder part tends to go out of round causing smoking in a lot of the motors. I did a set on a 1582 36 hp motor at stock bore and we cut the aluminum slightly in the stud areas to get clearance and a lot of the aluminum just fell off the iron part of the cylinder. The cylinders are just too thin to stay round even in a stock motor. The ones to use are just plain 356 iron cylinders from 1959 to about 1964. These are thick and round as well as cheap, they will take an 83 mm bore easily.

I'm not trying to burst your bubble or kill your enthusiasm, just my take on my 50 years of Porsche experience.

Bvilletom
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bvilletom
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[Alstrup]

Interesting.
I have had my thoughts about cutting the top fin off. - These are seasoned cylinders. If anything is loose I think it will soon show when we start cutting them. If they are as bad as you describe we will stop right there and seek another solution. If they hold up I think I will continue and see how it goes. - I do hear what you are saying, so I will go into this with open eyes so to speak.

T

[Mr. Motorhead]

I'm going to use mine since most everything is already done and I'm not really heavily invested in the set. I got the P/C set along with some other parts I wanted (I didn't want the P/C set). In fact, the aluminum valve cover sets were all I wanted, but most deals are "take all" so here they are. My Birals look pretty low mile and most likely were replaced when they became mosquito killers (smokers). The bore job to 83mm was done good but with a rough stone just a bit undersize. I finished them with a finer grit stone. They are actually round when checked with a bore gauge. We'll see how long they stay that way. This is a replacement engine for the stone stock engine in my 60, that engine is just about ready to do the 500 mile teardown on. It runs really good but I want to see what the wear patterns look like on the parts and make a couple small changes. As soon as I get heads back from being welded I'll be pretty much ready to build the big bore engine. Once built I'll do the swap and do the break in on it, run it for a while and take my time on the stock engine. When it turns out to be a smoker, I'll change to the iron set I have that I'm lacking one barrel for (anybody got a 82.5mm barrel the can give up?).
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30 years experience in the sales of new and used auto parts!
36 horsepower parts for sale at http://www.aircooledresearch.com/
Or the new site at http://www.bugparts.com
Check out the Bonneville project:
http://aircooledresearch.com/docs/thebonnevilleproject.html#

"All limitations are self imposed."
Some Chinese guy

[splitpile]

We tried birals and just got to thin when bored and machined to fit (I have a some extra cylinders if anybody wants them) . I just use 82.5 iron porsche or have some 80mm porsche bored out to what size I need. No need to machine the base and very little in the case and heads to fit. Couldn't make porsche big bore work YET bur think I got it figured out now
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[Low Bräu]

For you guys that have used the cast iron Porsche 82.5 cylinders on a 36hp or 25hp case. I realize the heads and case requiring machining but how much clearancing, if any, is required on the fins to make them fit? Is it anything as intensive as modifying the 83mm 40hp big bore jugs? Also will they work "easily" with 10mm head studs?

I have a worn out set of the iron Porsche 82.5 pistons and cylinders that I'd like to bore to fit 83mm pistons and use on an aluminum 25hp case. I'm only at the parts gathering phase and the cylinders were free so no loss if its not a viable option.

Thanks.
j.
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[earthquake]

Has any body tried to talk AA to make a 83mm [or bigger] Big Bore kit for the 36hp? I would not think it would take much extra work.

Casey
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[mark tucker]

I thought aa made birals for that?..or was that the porch motor.. probably the porch. I wonder how thier brials hold up.I was thinken about using a set of thier type 4 brials on a type 1 94mm bore.still in the thinken mode.