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Just got the pistons and rods back!!

 
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af2
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Joined: 01 Sep 2003
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Mon Apr 24, 2006 7:58 pm    Post subject: Just got the pistons and rods back!! Reply with quote

The Crank is still at the machine shop getting balanced. The Mahle pistons measured at less than 1/2 gram. The rods were at 1.5 grams. That is totally cool but the bob weight is more than 200 grams below! The reason that sucks is because The crank is set for a 1870 Gram bob weight and I have about 1620. So here we go again.
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Big Dave
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PostPosted: Mon Apr 24, 2006 8:31 pm    Post subject: Reply with quote

Boring holes in a crank is a much better problem to have than adding heavy metal. Any chance your machinist could pendulum cut the weights to lighten crank while reducing it's rotational inertia? (Gun drilling throws helps also). Cool

Big Dave
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af2
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Mon Apr 24, 2006 8:49 pm    Post subject: Reply with quote

Big Dave wrote:
Boring holes in a crank is a much better problem to have than adding heavy metal. Any chance your machinist could pendulum cut the weights to lighten crank while reducing it's rotational inertia? (Gun drilling throws helps also). Cool

Big Dave


Gun drilling was done when I bought it. That is the problem. He has to grind the top of the counter weight to get it to come in. He will knife edge and re check then do it again until right. This guy is the best at taking his time and making the crank right. He has already removed the crank 2 times and reset the balancer just to make sure. I couldn't ask for any better service period. Adam
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af2
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Tue Apr 25, 2006 4:37 pm    Post subject: Reply with quote

Big Dave wrote:
Boring holes in a crank is a much better problem to have than adding heavy metal. Any chance your machinist could pendulum cut the weights to lighten crank while reducing it's rotational inertia? (Gun drilling throws helps also). Cool

Big Dave


Dave thanks for the insight, I went to the machine shop today and they had the crank balanced perfectly. He even spun it to show me. The weights are now pendulum cut which is the only way to get it correct. He will polish the crank today and I can pick it up tomorrow. By the way the hole on the rear counter was already to deep to even think about going more. It was in the exact area to have more weight taken away so now I have a few smaller ones instead.
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af2
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Joined: 01 Sep 2003
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Tue Apr 25, 2006 9:20 pm    Post subject: Reply with quote

Just so everyone knows it took 63 turns to get the top ring at .018 clearance and 14 turns to get the second ring at .016 The oil rings were at .020 so I don't have to worry about them touching. You got to love good rings Smile That was with a good ring grinder. Laughing Adam

Last edited by af2 on Tue Apr 25, 2006 10:21 pm; edited 1 time in total
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Tue Apr 25, 2006 9:33 pm    Post subject: Reply with quote

af2,
What was the % over balance you put in it to keep High rpm vibrations
down? I know it is common practice to overbalance a certain %. I was just curious if you knew the answer in your particular buildup?

This article sort of states what I am talking about.

http://circletrack.com/techarticles/ctrp_0504_engine_balance/
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af2
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Joined: 01 Sep 2003
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Tue Apr 25, 2006 10:35 pm    Post subject: Reply with quote

Paul P wrote:
af2,
What was the % over balance you put in it to keep High rpm vibrations
down? I know it is common practice to overbalance a certain %. I was just curious if you knew the answer in your particular buildup?

This article sort of states what I am talking about.

http://circletrack.com/techarticles/ctrp_0504_engine_balance/


From what I saw it is 51/49. It might not be the best but the motor will see 8500 only a few times within seconds. With the modern balancing equipment these days there is no more guessing on were to drill the first hole. The computer tells you that.
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af2
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Joined: 01 Sep 2003
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Wed Apr 26, 2006 9:28 am    Post subject: Reply with quote

If I had looked at the calcs he wrote, last night I would have been able to tell you 52% over Embarassed Adam
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Thu Apr 27, 2006 9:25 am    Post subject: Reply with quote

Af2,
Cool hope it see 8500 many times Cool. Interesting though about over balance keeping certain harmonics from causing havoc.
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Big Dave
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PostPosted: Thu Apr 27, 2006 3:37 pm    Post subject: Reply with quote

A lot of what you consider over or under balance is subjective because no one really knows how much of the rods weight is actually contributed to the bob weight. It is at best an educated guess do to the dynamics of the engine. Some balance on CG others on a friction scale, but they are still an approximation. I would like the rod manufactures to do some Spintron testing to determine for a given rod profile and piston package a quantitative point for determining the rods contribution. That is one of those philosophical questions that has bothered me for a while (not as vexing as the number of angels that can dance on the head of a pin but it's up there).


Big Dave
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af2
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Joined: 01 Sep 2003
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Fri Apr 28, 2006 7:35 pm    Post subject: Reply with quote

I do know one thing! After racing 2 strokes For many years an over balance is the way to go when spinning 10,000 rpm. It has been proven first hand. I was not sure where Paul was going. Now I understand. Confused
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