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Mon Mar 17, 2014 6:58 am

Not directly VW related but I need some help.

I have a 1973 Haflinger 4wd - its engine is a twin cylinder 650cc horizontally opposed engine of a similar design to VW engines - conveniently VW pistons and barrels fits.

My Haflinger has a Mahle 87mm Hi Compression VW big bore kit fitted by a previous owner taking is capacity out to a whopping 762cc.

Unfortunately I have cracked a piston an need to get another and maybe a barrel.

I have searched and searched but cannot find anywhere I can acquire a new Mahle piston to match the one I require. All the 87mm Mahle pistons I have found on VW websites have all been flat top pistons where mine has a small raised section on top of the piston and recesses for the valves.

The following is a pic of my good piston.

My simple request is to ask if anyone has the same Mahle piston and where I might be able to find one.

Thanks for your time and any help you can give.

Garry

Canberra
Australia

Mon Mar 17, 2014 8:55 am

look on the under side of the piston; is that dome bolted on?

Mon Mar 17, 2014 10:28 am

have you checked pin hight to see if it has just been turned down so the center is raised? if not ,then you could have a set of forged pistons welded up and machined the same as what you have there and then ceramic coat them(tops).it should be fine. and dont forget to balance them too

Mon Mar 17, 2014 4:33 pm

Another option might be to send the broken one to one of the larger piston companies like Wiseco, or JE for a replacement. I'm sure they could 3D scan it, and make you a replacement. It won't be cheap, but might be a better option than trying to source a NOS version of what you have.

Mon Mar 17, 2014 5:53 pm

Thank you for your responses - much appreciated.

The raised area is not bolted onto the top of the piston.

The raised area has not been turned up post production by Mahle - the valve slots obviously have to be in the casting but there is also an engraving that is hard to see but is there indicating the piston is 86.5 SPO in the dot type engraving so this would have been put there in the production process.

I have my engine builder looking for an alternative from the various measurements and if he has no luck maybe I need to get one made.

I am currently going through 3500 piston entries in the Mahle catalogue.

Cheers

Garry

Mon Mar 17, 2014 7:27 pm

is the pin diameter the same? 22mm? and what is the compression height?

might just need to get two new flat tops, and lose some compression(if you can't take away deck-height)

I know some early Honda? pistons were almost shaped like that, raised flat dome, but 4 sets of valve cut outs

piston design has changed a lot over the years, so what was available back when, ain't available now

Mon Mar 17, 2014 8:47 pm

Ah, for the good old days - there's a company here that used to machine blanks to replace just about any piston. Having said that, check out your local bike shop, especially if they deal in antiques. It's still fairly common to need unique pistons in this field, so someone has to be doing it.

Tue Mar 18, 2014 3:21 am

Again - thanks for the responses - yes if all else fails I can just bung in the standard flat top 87mm pistons but I would loose some compression so was trying to track the piston first before looking at other options. One guy suggested going to 88mm to recover lost power but what I have read about 88mm barrels indicate the walls are too thin for a small engine that operates at hi revs all the time

I did ring one piston maker and he wants the equivalent of $1200US for two pistons :shock: . My engine builder has recommended another place and will try them tomorrow.

HOWEVER I did find out why I cannot find anything on this piston. I managed to track down the guy who built my engine and he told me where he got the pistons and barrels from. He got them from a VW specialist in Hobart Tasmania who also operated a helicopter that used these pistons (I assume the helo used the aviation version of the car engine). He imported 10 sets of pistons from the US for the aircraft and sold one set to the guy who previously owned my car. Apparently they are no longer available :( but I have asked the special engine department of Mahle US in the hope they may have some lying around.

As the kits came in sets of four barrels and pistons, and the engine in my car is only two cylinders I asked where the spare two pistons were - the guys house and all his parts got burnt down in the Tasmanian fires this time last year. :(

So it looks like a standard set of VW big bore 87mm pistons and barrels will be the way ahead - I have heard that AA are pretty good these days.

Thanks for all the suggestion that have been provided - I appreciate it.

cheers

Garry

Tue Mar 18, 2014 5:40 am

A Haffy... cool!

Tue Mar 18, 2014 5:49 am

WTF is a 'Haffy'? :lol:

Tue Mar 18, 2014 6:42 am

Can you run the flat tops, and then just flycut the head down to make up for the lost compression?

Tue Mar 18, 2014 9:39 am

if it uses a vw style rod by chance, use a longer rod,the forged or aa piston&then cut the top& add valve knotches.I would stay away fron the std cast mahle stuff. also look into the ford 4.6&5.4 modular pistons. or toyota, there are many that use the 866 pin(22mm) that you may be able to use. good luck

Tue Mar 18, 2014 3:37 pm

madmike wrote: WTF is a 'Haffy'? :lol:

It's a little, weird, Austrian-made forward control 4WD pickup

Tue Mar 18, 2014 3:41 pm

how tall is the dome?

Tue Mar 18, 2014 4:13 pm

I have a friend in town that has two of those vehicles and may have spares. His are original though not punched out to larger CCs.

Tue Mar 18, 2014 5:38 pm

If you go to 5.5 length rod you can cut a regular piston to the same shape.

taking .100" off the piston is a bit much but .070"or .080" should be ok, then adjust deck height with cylinder spacers.

Tue Mar 18, 2014 6:35 pm

I'd adjust the deck with a bigger crank.

:twisted:

Tue Mar 18, 2014 6:38 pm

I was thinking the same thing. Offset grind to 2" for a 72 stroke and that's about perfect.

Of course maybe they didn't use the 69mm VW stroke? Great minds think alike maybe it is already 70somthing stroke

Tue Mar 18, 2014 7:19 pm

I was thinking offset grind the crank, then turn down the piston top to a domed center, up against the head

Wed Mar 19, 2014 5:31 am

The Haffie has a 64mm stroke and standard has an 80mm bore.

Well I have spent some time with my engine builder and as some of you have surmised the piston has in fact been cut down. The main reason we initially thought the piston was not modified was the lathe marks were consistent across the top and the original dot matrix style engraving still existed - but was on the main flat across the top.

So this piston started life as a piston in a 87mm big bore kit for the aircraft version of the VW air cooled engine.

The builder has sourced a suitable kit with pistons that have enough meat in the crown and he will turn these down like the ones I have and mill the recess for the valves. I only need two pistons and barrels but of course you have to buy four so I will the spare two sets modified for further use.

Thanks for all the feedback and comments - has helped me work out what I have and how to proceed.

I appreciate your help.

Cheers

Garry