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Fri Aug 19, 2005 5:23 pm

Has anyone successfully used the new Mahle 83mm big bore 40hp pistons and cylinders?

After assembling the case and fitting the pistons to the connecting rods, number 3 piston locks up against the internal stuff just the other side of where the cylinders sets, flywheel side of the case.

I don't have another 40hp case lying around to compare to see if mine is freaky. However comparing the old big bore 40hp pistons to the new ones, there are obvious differences. The old set wears short skirts while the new set wears a longer skirt. Remember the time before digital cameras, when ASCII ruled? Well, that's where I live and I'm no artist. Imagine o, wrist pin hole, as hanging over the center of each picture.

o
_| |_ (Old set, side view)

o
_ -- _ (New set, side view)

So, blah, blah, blah, anyone using the new Mahle big bore 40hp P&Cs?

Fri Aug 19, 2005 5:24 pm

sure its for 40 horse and not something else?

Fri Aug 19, 2005 11:05 pm

I'm guessing they're cylinders for a 1500 -- were they specifically sold as big-bore 40 HP?

PM glutamodo and see what he says.

Sat Aug 20, 2005 7:10 am

Yes, I built an engine using the 83mm big bore kits. I didn't have that problem, but it might happen. You might have to shave the piston so it won't interfere. Of course, you will then have to weigh that one and take the same amount of material off the other pistons. As for the speculation that they could be 1500 pistons, the bore size in the case is different for 40hp and 1500. So if the barrels fit in the case with the kit she has, they are correct.

Sun Aug 21, 2005 2:20 am

Or, 1966 1300cc, as the bore was 40hp size and the stroke was 1500 size. This could be found by checking the "big bore" cylinder height compared to the 40hp cylinder.

Sun Aug 21, 2005 6:44 am

Ah, Ha! 1500 and 1300 cases have the same cylinder bore, so Roy's answer is the best, so far. Even though Clymer states, no machining necessary with your size kit.

Sun Aug 21, 2005 10:26 am

All new cylinders fit well into the 40hp case and all pistons revolve fine except for number 3. What I've started to do to "machine" the case. Considering the chain of events if the weight of one piston is changed and having done something similar with heads (ug!), it just felt better removing some material from the flywheel end of the case.

Anyway, very glad to read that someone used the new 83mm big bore 40hp pistons and cylinders without problem. I guess that might mean that the case is freaky, I'll probably find out much too late that it's a "bastard 40hp" though the gallery between number 3 and 4 looks just fine.

Sun Aug 21, 2005 11:03 am

I might suggest you check with your supplier of the kit. Possibly, the person who packaged your kit included the wrong pistons. The area you are macihning for clearance is an area the usually cracks in stressed blocks. Also, remember what clears by you turning by hand may not clear at 3,000 rpm. Are your old pistons useable at all? Good luck!

Mon Aug 22, 2005 11:02 am

Rachel- are you the lady who drove the '50's single cab pickup on the 50th Anniversary Ghia trip this summer?

Mon Aug 22, 2005 4:36 pm

volksman4u wrote: Or, 1966 1300cc, as the bore was 40hp size and the stroke was 1500 size. This could be found by checking the "big bore" cylinder height compared to the 40hp cylinder.

You are correct in stating the bore on a 1300 was 77mm and the stroke was 69mm, but the spigot size in the case of the 1300 was larger than the 40hp. Therefore, 1300 jugs will not fit a 40 hp case without machining. Also the big bore 40hp kit is 83 mm instead of 77mm.

There seems to be a lot of confusion centering around the 1966 1300 type 1 engine. The crankcase of that engine has the same cylinder spigot dimensions as a late model 1600 DP motor has and it has the same stroke crank. You could turn a 1300 into a 1600 without machining to the case by simply swapping pistons and cylinders. You would however have to open up the 1300 heads or swap to later 15-1600 heads.

Thu Aug 25, 2005 12:49 pm

I'm just wonderin where you guys did find those new P/C kits 83mm bore to fit in my 40hp. I'v been looking around a bit but to no avail. But it could be just me. Some pointers please?

Thu Aug 25, 2005 1:39 pm

DVF'er Tim wrote: I'm just wonderin where you guys did find those new P/C kits 83mm bore to fit in my 40hp. I'v been looking around a bit but to no avail. But it could be just me. Some pointers please?

I bought mine at BFY Obsolete Parts earlier this summer. Recently I have seen them here in the classifieds.

Fri Aug 26, 2005 10:19 am

The best price I've seen on the big bore kits is from Serrano.

So does anyone have any advice for rachel that is related to her question or are we gonna splinter off and talk about something else? what is this the VB list? LOL

Rachel, I checked and I have COFAP's ...

Fri Aug 26, 2005 4:36 pm

big bore 40hp pistons have 20mm wrist pins. 1300-and up have 22mm wrist pins. the pistons in question are 40hp big bore, and there is a definite visual & physical difference between the old pistons and the new ones, and a definite clearance problem. i'll let rachel fill in the details. this set did come from serrano.

Fri Aug 26, 2005 9:52 pm

I paid someone who lives in the current decade to take the pictures posted here:

http://www.thesamba.com/vw/forum/album_search.php?..._terms=all

Mon Aug 29, 2005 9:35 am

I missed this thread, (worked the last 4 nites and I don't read the performance/engines board usually) but I found it now and dug into my parts pile to do some comparisons. I have a set of new old stock CIMA brazillian P+C's (a similar set is which is what I'm running in my 62 right now), some used P+C's from a previous engine of mine, which had I believe had COFAP brand from sometime in the 1990's, and a set of the new Mahle ones I bought to throw on my parts shelf while they were available. I hadn't compared them though.

I cleaned up one of the used COFAP ones. I think that arrow logo is the COFAP one, although inside the piston there's the K-over-S logo that I think is Kolbenschmidt, but I suspect COFAP was usuing old kolbenschmidt tooling to produce these. I didn't get all the gunk off of it, but most of it. I also weighed the three, (weights include the wrist pins.)

1984 CIMA - long piston skirts, and the heaviest weight at 494grams

1990's COFAP - shorter piston skirt, and was the lightest of the three at 462 grams

2004 MAHLE - total piston height was the same but the amount of skirting was much less. With the more metal it was heavier at 478 grams.

Looking at these, I can see how the skirts are "fatter" on the MAHLE one, and that must be the clearance problem. I think I'd reshape the piston skirts myself, instead of the block, making sure I did the same to each piston of course and verifying they stay at equal weights on a scale.

Here's some pictures: (I usually shrink my pics down to 640pixels wide but in this case I'll leave them larger)
The pistons are, from left to right in all pics: CIMA COFAP MAHLE
(as always, click on the picture for the full size image.)

-Andy

Wed Jan 03, 2007 3:42 pm

2 of my mahle barrels got damaged in transit, anyone got or know someone who wants to sell? or odd ones? :(

Fri Jan 05, 2007 4:09 pm

Given the option to go back in time, I would get another manufacture of big bore pistons and cylinders - not the Mahle manufacture.

Cost of complete but knocking big bore 40hp engine = $40
Cost of Rimco machine work (align bore, grind crank, recon rods, bore for cam bearings, 10mm case savers) = $218.75
Cost of new Mahle big bore pistons & cylinders = ~$150.00
Cost of rebuilding a big bore 40hp in anticipation of vintage speed and bus camping... and, a couple of hours later, discovering that #3 piston inexplicably locks up against the case = priceless

However if time is money, the cost of this venture shoots up exponentially. Normally my time is cheap but the fiasco cost me four camping trips, a backroads adventure and a great deal of frustration.

I believe that much of the situation could have been improved by communication. I like to resolve issues in a collegial manner despite what I might feel or have to say about the situation precisely because there are factors at work beyond my petty situation.

While #3 completely locked up against the '61 case beginning the adventure, it turned out that all of the other pistons contacted the case as well and all needed clearancing, even #3... and even after the case had been clearanced by Serrano on the #3 and 4 side.

There were other issues as well and after the frustrations and missed VW events, I pretty much handed the project over to another engine builder. According to him there is no way to clearance just the case or just the pistons and in fact, both case and pistons needed clearancing to be used. We suspect that the pistons and cylinders are for another type of engine and not actually for air-cooled VWs.

Fri Jan 05, 2007 4:29 pm

I agree that those look like non-VW pistons too.

Fri Jan 05, 2007 4:37 pm

I had the same problem but all of my pistons hit.

I just worked the case because I was uncomfortable cutting and weighing my new pistons equally.

I did make a cool template though.

Here is how I intended to cut the pistons:

I marked the areas to be removed in black.

All said, if I was consistent with my marking and cutting, the pistons would have probably been close to 'as balanced' as they were at first.

I say this because I was surprised at how out of balance my new Mahle 94mm B pistons were.