Stan.Shaw@Excell.Net

Do you know the weight of the rods, as well as the rot. and recip. weights?

I am guesssing tolerance group 1 due to the markings in this photo.

John Veninger

Any update? Second opinion yet?

Stan.Shaw@Excell.Net

No second opinion yet. I am waiting to see how Adam B. does with his first.

Vilhuer

That is group 1.

That number also points which side of the piston should be facing forward in 968 engine in case markings on top of piston are impossible to see. Clearly larger intake valve cuts on piston tops will tell same thing. But since exhaust cuts need to be modified so that pistons can be installed on drivers side and thus is not possible to see which side needs to be on front looking at cuts, its nice that factory have provided easy way to decide. If all else fails its obviously possible to measure actual wrist pin offset and use that as guide.

atb

Sorry about the delay guys, I needed to make sure that I could still run my new pistons with their incorrect piston height. Got that situation squared away and can now take my components to the machinest for balancing. He's reduced his office hours to four days a week. I can't remember if he's closed mondays or fridays, so I'll either get the stuff to him today or monday.

Stan.Shaw@Excell.Net

Thanks Adam, no rush, just curious is all.

atb

Just got back from dropping off the parts at the machinest's shop. I told him we we're going for a world record, and he got a very serious look on his face (like crap, this is friday, there goes my weekend) but he had a good laugh when I said it would be for the world record for the amount of Mallory ever put in a crank. I'll post as soon as I hear from him, hopefully by the end of next week.

Stan.Shaw@Excell.Net

I was reviewing my notes, and realized they (the machine shop) must be confused. While they say the 2870.2 has nothing to do with my crank balancing, you can see (in the original post) that they subtracted my bob weight from it.

Does anyone know "what" a bob weight would be subtracted from in a dynamc balance?

The suggestions of getting a second opinion seem right on, but I may pay another visit, after all I paid $100 for their efforts....

atb

I'll get the calc from my machinest so we can compare if no one has the info before then Stan.

Vilhuer

Any updates on builds mentioned in this thread? Haven't noticed much stroker talk lately.

Today I measured individual part weights. Results below if anyone cares.

Modified 968 pistons (exhaust valve cuts are same 39mm as intakes) 489.9 - 495.9g
S3 wrist pins 142.0 - 142.4g
968 wrist pins 158.1 - 163.8g
Clevite 77 upper rod bearing 22.6 - 22.7g
Clevite 77 lower rod bearing 22.5 - 22.6g
ARP rod bolt 34.4 - 34.7g
Eagle 5.85" rod upper part (pin hole modified for Porsche pins) 422.4 - 423.5g
Eagle 5.85" rod lower part 155.0 - 156.2g
Pin lock ring 0.9 - 1.0g
Oil ring 12.8 - 13.1g
Secong compression ring 16.9 - 17.3g
First compression ring 14.9 - 15.0g

Total counted from smallest number is 1369.9g for S3 pin and 1386.0g for 968 pin. Scale goes to 1/100 of g. Many small parts are actually closer to each other than rounded numbers indicate. For example lock rings are between 0.94 and 0.98g. Piston rings will also need to be measured for end gap and modified to fit which could change their weight ever so slightly.

Rod numbers are not same as what is used in bob weight calculations. If I have understood correctly rods large end needs to be measured on special scale and same result can not be achieved on ordinary scale I have on loan. Thus I can't calculate what actual bob weight is going to be. But using rod weights posted in #1 message as baseline and taking into account that mine are probably heavier, resulting bob weight looks to be large.

Using same 175.5g and 466.0g as in other calculations gives 1881.7g which would not be too bad I quess if Moldex crank is ok for this kind of weight as I suspect. Crank has lost some weight since crank arrived as counterweights are now modified to allow little over 1mm clearance between weight and piston on BTC. Taking out metal took few days with grinder. Shiny parts on weights is where material was removed.

http://www.youtube.com/watch?v=hTrl2Acrlnc
http://www.youtube.com/watch?v=E5uCM4CWYSs

Now big question is, how much larger reciprocating and rotating rod weights are with these rods? Eagles including bolts are 646g after wrist pin mod. I tried to find rod weight for rods 175.5g and 466.0g numbers are for but couldn't.

Stan.Shaw@Excell.Net

I haven't moved forward since my initial problematic attempt. I need to do a test assembly first, but at this point I am inclined to talk with Adam's machinist and see if he thinks he can balance my components as he did Adam's. I would rather ship across country for a sure thing, then take another foray into unknown territory.

atb

I got a call from my machinest last friday that the balancing was done, but that the new wrist pins from ROSS weren't to his standards. He thought the fit was too tight, and wanted to polish them down to the proper clearance. He said it would be done at the end of this week. I'll get all the specs then.

Vilhuer

175.5g + 466.0g = 641.5g. Thinking about rod weight little more that must be weight of those rods. Othervise formulas would not make sense. I hope thats correct as it would mean mine are only 4.5g heavier then. In bob weight this would mean 1890.7g in worst case where all extra weight is on one end. Balancing starts to look possible or perhaps even easy if you guys can make 1800g+ work with six counterweight crank.

Stan.Shaw@Excell.Net

Please ask him if he will balance mine too, my numbers are at the beginning of this post. Or ask if I can call him to discuss sending my parts to him as well.

Thank you kindly sir

Fastest928

"polish" them down.....if you want them done right, they can only be centerless ground.

might wan to check on this