I am Lost...

hobieboy · 04-11-2006, 05:51 PM

ok - its not really me but what to do????

I measured the weights of my pistons. 4 of them are within 2g, but there are 2 lighter ones - they are 8g lighter than the heaviest but they are also opposing each other (from cylinder 3 & 6).

The Porsche spec says 8g is maximum service tolerance for turbo pistons. So, I'm right on edge.

Yes, the easy answer would be to get new ones. But, being cheap, what is the downside of being "slightly" outside tolerance? Will it break the bottom end? What are the consequences / side effects?

Walko · Walko's Garage

I would put five of them on a diet to match the lowest one in weight?

Michael

hobieboy · 04-11-2006, 05:56 PM

The machine shop I took it to looked at them and say there's no way they can take even 4-5g out (let alone 8g). These are also short skirt pistons so not much room to take material off.

camgrinder · 04-11-2006, 06:19 PM

Are you measuring them with the piston pin? Sometimes the pins vary in weight and the heavy pin can be used with the lightest piston?

hobieboy · 04-11-2006, 06:29 PM

Yes, it was measured with pins & rings (which are new).
Silly me to decide to weigh them after I install / matched the pins to the rod (with new bushing)

shbop · 04-11-2006, 06:56 PM

Just curious about your scale. What are you using? Where did you get it? I need to weigh some parts as well. Sorry to jump-in on the thread.

Aloha, Jon

camgrinder · 04-11-2006, 07:07 PM

Someone I know just bought a digital scale on ebay like this one listed in # 7550440095 repeatable and cheap.
There a lots of them to choose from.

Henry Schmidt · Henry Schmidt's Garage

Funning you guys are talking about wrist pin weights. When we balance pistons we remove material from the inside of the wrist pin. Most stock pins are very thick and you can remove a very large amount. We use a small engine lathe for this work. If you have two light pistons, you might be able to find heavy pins. weigh them and call. We might have heavier pins to suit your needs.
The fact that the light pins were opposite in the engine suggests that the last builder knew they were lighter than the others. On a horizontal engine when opposite pistons weigh the same the engine will generally run smoothly.

shbop · 04-11-2006, 09:34 PM

Thanks John!

Jeff Alton · 04-11-2006, 10:54 PM

That is just like the scale I use, very repeatable and seems to work very well.

Cheers

hobieboy · 04-12-2006, 03:35 AM

Henry,
Would it be possible to take material off the inside of the pin?
In my case, I have already sized the rod bushing to the pins, would I need to take the bottom end apart if I replaced some pins with heavier ones?

thanks...

philippeF · 04-12-2006, 04:16 AM

here's what i did :

8g material inside the "too light" pin, heavily inserted (pressed ?is the word ?)

lindemans · 04-12-2006, 10:45 AM

Quote:

Originally posted by philippeF
here's what i did :

8g material inside the "too light" pin, heavily inserted (pressed ?is the word ?)

Oh my, if that one ever gets loose.....

I would definitely look for heavier and lighter pins within the set you have and have matrial removed from the inside of pin of the heaviest set.

philippeF · 04-13-2006, 03:06 AM

well this is a question i asked myself.....
But is there any reason it comes loose ? I don't think so..
What are you thinking about that, you, old experienced men ...

Philippe

Mike Juzenas · 04-13-2006, 07:30 AM

Quote:

Originally posted by philippeF
well this is a question i asked myself.....
But is there any reason it comes loose ? I don't think so..
What are you thinking about that, you, old experienced men ...

Philippe

I am thinking about all the vibrational harmonics etc. that happen while this mass is being moved back and forth rapidly. I guess it depends on how tight the press fit is, does the press fit change depending on he temperature gradiants that could happen, is there any sideways motion, etc.

If this were my car I would rather machine down the heavier piston's wrist pins to all match or order heavier pins from Porsche to offset the lighter pistons with the intention of having the pins be one piece with no inserted sleeves. This solution would bother me especially winding the car out on the track. But to each to own!

No science involved just gut instinct! ;-)

Cheers,

Mike

lindemans · 04-13-2006, 07:49 AM

You never exactly know how the pressed components will behave under temperature loads, vibrations and other dynamics.
It may very well last forever; yet I'd be concerned that the inserted part is not restricted in its movement if it would come loose. The circlips won't keep it in.

Nevertheless the idea is very creative and I am sure that keeping far tighter tolerances in weight of parts will increase the smoothness of the engine

afterburn 549 · 04-15-2006, 01:58 PM

Tell ya a secret of my stupidity so shhhhhh. In the middle of the night was weighing stufff made a mistake and took lot of material out of the lightest piston.........euggg ugh....what to do now ??? Made the rest match !! now I have pistons lighter then any Porsche category listed and about 10000 hard beat em miles on them.......there still still there going suck boom bang. ( so I think you can get away with it )