Fit of new Mahle big bore 40hp P&Cs

[Rob E UK]

im just about to fit my b&p's after having them machined down on the piston skirt and rebalanced.

anyone comment on the power increase?

[glutamodo]

All the 40HP engines I've ever driven were already big-bore'd so I can't really say how much of a difference you'd notice between the two sizes.

[the.fordhams]

A big bore kit will be noticeable - for me it took my vert from a 60mph machine to a 70 mph machine. This is subjective but as a comparison my 1600SP ragtop is a 75-80mph machine. Different gearing weight etc but hopefully you get the idea.

Rgds,

Al
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[rachel]

According to one source, regular 40 horse engines are 1192cc and a "big bore" 40 horse engine is 1385cc; those 200cc extra may make a big difference to a VW.

I think that the 40 horse in my bus is every bit the engine as the 1600SP in another bus but at a reduced top speed. Top speed for the 40 horse is 55MPH, top speed for the 1600SP is 65MPH.

The running gear in the 40 horse is stock-ish - the transmission, RGB, axles and backing plates are out of a '60, shifting into fourth gear is at about 30-35MPH. The running gear in the 1600SP is modified - the transmission is a 12-volt non-freeway flier, RGB axles and backing plates are '63 one-ton, shifting into fourth gear is at about 40-45MPH.

[House]

Has anyone tried machining the new piston skirt to be similar to the old one to get around the clearance issue yet?
Or are you just knocking down the edges...?

[glutamodo]

"Gerg" above has a dead link for a photo, it used to show how he was going to reshape his skirts. The important thing is to be uniform - all the pistons need to weigh the same when you're done, so just cutting the one or two pistons that hit the case isn't probably the best thing to do.
-Andy

[House]

I was thinking of just machining the "New Mahle" to look like the "90's Cofap",
balancing them, and calling it a day...
Just wondering if anybody else has been doing that or are they hand
fitting / clearancing the troublesome one and then balancing the others to match.
I know this must come up quite often, I am surprised there isn't more talk about it.

[TomSimon]

while working on a project with my friend Greg Urrutia, we started talking about the big bore 40hp conversions we'd experienced

"When I worked at this independant shop back in the day" he said "our happiest customer was the one who brought in a tired 40horse and left with a big bore kit.... they usually called back later and said it was never that powerful when new, a completely different car!"

That was about the same as my one and only experience with a big bore 40 kit, my 63 ragtop (that I drove in college) was fun to drive again!

[JHvolks]

[64vdub]

Has anyone used the "AA" brand of 83mm big-bore pistons? Not sure if they would need to be clearanced too. Thanks.
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[Chuey]

Wolfsberg West sells 1385 kits. They should know if they need modification.

Chuey

[glutamodo]

Well, if they are the Mahle kits, they are probably going to need it, depending on your engine case.

I've not seen these AA big bore kits myself. I was just looking at the AA website and I'm not seeing where they sell kits they made themselves. There's a listing on AA, for the MAHLE sets that I found, which look like this:

but when you click on it, it says "Sorry, the product was not found."

[OvalWindowBucket]

I bought a set of AA 83mm Big Bore p&c from Mr. Motorhead (samba user). I can post pictures of the pistons/skirts soon, but I have not mocked up my motor to see if there are clearance issues.
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[JHvolks]

The 83mm mahle pistons that I mentioned in the above post ( that I had to grind down) were purchased from WW.

After I ground the buggers down, they were amazingly within 5 grams
of each other, so I balanced to one gram. they've been in the car and have about 4000 miles on them......runs great....very peppy & 31mpg.


Jeff
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[glutamodo]

[Mr. Motorhead]

Okay, I changed the picture. The AA pistons are an almost carbon copy of the Mahle 83mm. I said almost. The big difference is the length of the skirt. The AA piston measures at 2 3/4" while the Mahle stands an 1/8" taller. It really does not matter what brand 83mm big bore pistons you buy........I've had clearance issues on some 40hp cases with all brands over the years starting with the Japanese NPRs that I started using in the mid-70s. The advice I always give on these and many other non-stock parts is make sure it all fits and spins clean with at least .040 clearance between parts that could collide.

Piston on the right is AA, on the left is Mahle. Both use the 2mm compression rings.
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[64vdub]

Are Mahle's are still made in Germany? I wonder if the AA are of similiar quality...I'm inquiring cause I'll be tackling my first re-build on a spare 40hp I picked up.
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[glutamodo]

Nope, not German. I don't know how long it's been since Mahle moved production ot Brazil but I think every new Mahle kit I've ever bought (83, 85.5, 87) in the last 20 years has been from there.

[hsosa1]

Where do u buy rings for a big bore? To use a 1600 cc crank do u need to clearence the case?
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[64vdub]

Not sure about the crank, but you'll probably have to shim the cylinders for the increased stroke.
_________________
64' Pearl White beetle, type 113 sedan. Purchased in Hamburg Germany, driven for a year via vw tourist program, shipped to CA in 1965.

Founding member of Derkaferklub, Southern Cal. since 2008

Q: Would you consider a trade? What do you collect?
A: I collect money


GO SF GIANTS!