Lighter Pistons, should I rebalance the crank?
04-27-2003, 11:02 AM
#16
Three Wheelin'
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">By dr Bob:
Do NOT try to adjust the counterweight mass to make up for a difference in piston weight. My recommendation.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica"> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">by steve cattenero:
I agree with Dr Bob
Balancing and blue printing or rotating and reciprocal parts are done individually.
The crank is balanced by itself; </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I guess neither of you bothered to read this page by an expert in the field:
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">by Z:
<a href="http://www.442.com/tech/balancing.html" target="_blank">http://www.442.com/tech/balancing.html</a> </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Have you guys had any hands-on experience on this topic that you would like to share?
Do NOT try to adjust the counterweight mass to make up for a difference in piston weight. My recommendation.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica"> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">by steve cattenero:
I agree with Dr Bob
Balancing and blue printing or rotating and reciprocal parts are done individually.
The crank is balanced by itself; </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I guess neither of you bothered to read this page by an expert in the field:
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">by Z:
<a href="http://www.442.com/tech/balancing.html" target="_blank">http://www.442.com/tech/balancing.html</a> </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Have you guys had any hands-on experience on this topic that you would like to share?
04-27-2003, 11:20 AM
#17
Burning Brakes
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by John:
<strong>........The big what if in my mind is leaving the crank counterweights as is. The post z put on here is a good one and confirms what I have been asking for the last few days.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">John,
I do not understand your conclusion - You said Z's post is good, and then you decide to do opposite
quote.
He said among other: "............The other problem is your new lighter pistons and rods. When we talk about crankshaft balancing, we're not referring to just that squiggly hunk of steel that resides in the bottom of your engine. We mean the whole crankshaft assembly, which includes pistons, pins, rods and rings. .................."
<strong>........The big what if in my mind is leaving the crank counterweights as is. The post z put on here is a good one and confirms what I have been asking for the last few days.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">John,
I do not understand your conclusion - You said Z's post is good, and then you decide to do opposite
quote.
He said among other: "............The other problem is your new lighter pistons and rods. When we talk about crankshaft balancing, we're not referring to just that squiggly hunk of steel that resides in the bottom of your engine. We mean the whole crankshaft assembly, which includes pistons, pins, rods and rings. .................."
04-27-2003, 01:50 PM
#18
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Quote; by Steve cattaneo
I Agree with Dr Bob,
Balancing and blue printing or rotating and reciprocal parts are done individually.
The crank is balanced by itself; the connecting rods should be within 0.1grams or each other in weight and balanced end to end.
The most critical parts are the pistons. The weight should match. Weight all the pistons the lightest one is the bench mark remove small portions of metal from the other 7 to match the lightest one. It is done by drilling the pistons. The rods are done the same way. Any engine machine shop can do the job.
I am sorry for posting a technically vague answer.
An addendum to my last post.
The pistons should be weight with the rings and wrist pins installed. Once you established the combined weight of the rods and pistons the shop assembles bob weights which are added to crank for proper balancing.
LAGAVULIN
The techniques for balancing and blue printing an engine in this country are not a secret.
BTW I have rebuilt exactly 50 engines mostly muscle cars.
How many have you done?
I Agree with Dr Bob,
Balancing and blue printing or rotating and reciprocal parts are done individually.
The crank is balanced by itself; the connecting rods should be within 0.1grams or each other in weight and balanced end to end.
The most critical parts are the pistons. The weight should match. Weight all the pistons the lightest one is the bench mark remove small portions of metal from the other 7 to match the lightest one. It is done by drilling the pistons. The rods are done the same way. Any engine machine shop can do the job.
I am sorry for posting a technically vague answer.
An addendum to my last post.
The pistons should be weight with the rings and wrist pins installed. Once you established the combined weight of the rods and pistons the shop assembles bob weights which are added to crank for proper balancing.
LAGAVULIN
The techniques for balancing and blue printing an engine in this country are not a secret.
BTW I have rebuilt exactly 50 engines mostly muscle cars.
How many have you done?
04-27-2003, 02:49 PM
#19
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A 928 owner I know of just assembled an engine, with short block components that were part of an engine project someone else never completed. JE pistons, and Pauter rods were used and came with the rest of the short block. Since this was basically all from an engine that was supposed to be ready to be assembled, it was implied that everything had been balanced when he bought it. It hadn't been. Even at idle, the completed engine very noticeably vibrated the entire car and trailer it was on. It's apart again and being balanced now.
04-27-2003, 06:23 PM
#20
Nordschleife Master
Somebody, please clarafy this for me.
Why is the convetion according to the web site 100% of the rotating mass, and 50% of the recepocating mass? Is the recopcating mass the top half of the rod, and the pistion, or just the top half of the rod?
Thanks.
Why is the convetion according to the web site 100% of the rotating mass, and 50% of the recepocating mass? Is the recopcating mass the top half of the rod, and the pistion, or just the top half of the rod?
Thanks.
04-27-2003, 11:26 PM
#21
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No, I think I am going to opt for the balance job on the crank. It just makes good sense and is real cheap insurance at $170.00
To say the crank is balanced by itself makes no sense at all...if you spun just a crank to 6000 rpm, what would happen?
My suspicions on this seem to be correct...that is it is bad practice to change piston and or rod weight without looking at the crank.
Perhaps the 928 with the Pauter rods is a worst case scenario, because the rods and JE pistons were much lighter? Anyway, I'll know more once the pistons arrive home here and I can actually weigh them.
With all that mass removed, the engine should rev more quickly than before. If it doesn't I'll just crank up on the boost ****...
To say the crank is balanced by itself makes no sense at all...if you spun just a crank to 6000 rpm, what would happen?
My suspicions on this seem to be correct...that is it is bad practice to change piston and or rod weight without looking at the crank.
Perhaps the 928 with the Pauter rods is a worst case scenario, because the rods and JE pistons were much lighter? Anyway, I'll know more once the pistons arrive home here and I can actually weigh them.
With all that mass removed, the engine should rev more quickly than before. If it doesn't I'll just crank up on the boost ****...
