Author Topic: ra/sb pistons (Read 3121 times)

gigaz2 · « **on:** July 23, 2008, 07:19:47 am »

I was taking my SB block apart when I got this:

piston:

injectors:

the head is original vw and is cracked everywhere, even behind the precups :O

these are Mahle 76.54mm pistons, I believe they were only used on these 80hp engines.
my question is: can I reuse them? I have better use for the 300€ I would spend on new Nural or Kolbenshmitt pistons...

the injectors also suffered from severe heat, as can be seen, I'm going to put new nozzles and calibrate them. they have the stock dnosd274 nozzles in.

Vincent Waldon · « **Reply #1 on:** July 23, 2008, 07:59:08 am »

My opinion: I don't worry much about the face of a piston... looks like that one has some erosion and has kissed the valves in the past... but gently.

What I can't see in your pictures is the parts I personally pay attention to... the ring grooves (with the rings removed) and the skirts.

The sides of the ring grooves are a sealing surface (against the sides of the rings) and need to be crisp crisp crisp. This is why I personally cringe when I see people removing crud from the grooves with an old nail or screwdriver... proper carbide-tipped tool makes much more sense to me.

The skirt is the axial load-bearing surface. A little scuffing is ok... lots of scuffing usually quickly leads to even more scuffing and eventually scoring of the cylinder walls.. at which point you will be into it for new Nurals, and an overbore.

One final thought: miking them might be a good idea as well... if they're substantially out-of-round or tapered you might be wise to pitch them before they damage the bore. In fact, miking the bore is probably also a good idea.

subsonic · « **Reply #2 on:** July 23, 2008, 08:05:39 am »

300 euro's is like 5-600US!!! Myke has them 300 US shipped, although to you might be a bit more.

gigaz2 · « **Reply #3 on:** July 23, 2008, 02:32:26 pm »

my main concern was that erosion right below the precups (which were cracked), every piston looks exactly like this one.

to me it seems that this is the outcome of some serious detonation and overheating.
I'll take a few shots of the grooves and skirts, and the bore as well.

Vincent Waldon · « **Reply #4 on:** July 23, 2008, 03:14:21 pm »

Because I'm in a picture mood today... I bet this puppy looks just fine from the top:

:shock: :shock: :shock:

gigaz2 · « **Reply #5 on:** July 23, 2008, 03:18:16 pm »

compared to that mine are brand new out of the box

I'm uploading the pictures of the skirts, post then in a minute.

EDIT: damn ISP, ftp is down, will post tomorrow.

gigaz2 · « **Reply #6 on:** July 24, 2008, 04:36:36 am »

here it is:

its the same piston as above (I only took one out), removed the rings carefully, cut myself in the process(nasty sharp buggers).
the ring seats look brand new and the skirt only has those minor scratches, I say they are minor because i can see the machining marks and can't feel the scratches with my finger.

so I guess I can get away with a set of new rings if all the other pistons are as good as this