Engine Balancing
08-06-2015, 03:22 PM
#1
Pro
Thread Starter
Engine Balancing
I am rebuilding a 944 Turbo engine as a street car. I almost have all the parts, just waiting on main bearings which weren't in stock in most places. Since my pistons were shot, I got some wossners and kept the same rods.
Since I am lightening the weight of the rotating assembly, will I also have to get the crankshaft rebalanced for the new bobweight?
Since I am lightening the weight of the rotating assembly, will I also have to get the crankshaft rebalanced for the new bobweight?
08-06-2015, 04:01 PM
#2
Rainman
Rennlist Member
Rennlist Member
http://www.laskeyracing.com/shop/balanceengine.htm
4 Cylinder Engine Balancing
Do not confuse balancing V-8's as compared to 4 cylinder engines. It is a completely different process. Since two cylinders are directly opposed to the other two cylinders, putting bob weights on the crank does not make any difference in the balancing measurements. The added weights just cancel each other out when spinning the crank. Aftermarket pistons and rods come balanced to within a gram. (That is very close when you consider there is 453.6 grams in a pound.) Clutches and flywheels also come spun balanced from the manufacturer. This is necessary in order to have their SFI certification. Same with aftermarket balancers.
The crank is balanced by itself with no weights attached to it. It does not make sense to add a clutch and flywheel to the crank when balancing because then you are stuck with the same flywheel and clutch forever unless you want to throw your engine out of balance or rebalance your crank after each clutch change.
As to adding the balancer to the crank when balancing, this is not done because you would rather read the out of balance condition on the crank itself and correct it rather than having the balancer mask that condition.
Do not confuse balancing V-8's as compared to 4 cylinder engines. It is a completely different process. Since two cylinders are directly opposed to the other two cylinders, putting bob weights on the crank does not make any difference in the balancing measurements. The added weights just cancel each other out when spinning the crank. Aftermarket pistons and rods come balanced to within a gram. (That is very close when you consider there is 453.6 grams in a pound.) Clutches and flywheels also come spun balanced from the manufacturer. This is necessary in order to have their SFI certification. Same with aftermarket balancers.
The crank is balanced by itself with no weights attached to it. It does not make sense to add a clutch and flywheel to the crank when balancing because then you are stuck with the same flywheel and clutch forever unless you want to throw your engine out of balance or rebalance your crank after each clutch change.
As to adding the balancer to the crank when balancing, this is not done because you would rather read the out of balance condition on the crank itself and correct it rather than having the balancer mask that condition.
08-07-2015, 06:55 PM
#5
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Save the money by the time your done with reconditioning the stock rods both big and small ends .You'll have spent around 450.0 to 500.00 add another 170.00 if you put in better rod bolts and still have the stock heavy rods for 250.00 to 400.00 more you can get a set of Woosners or Cerullo's .There lighter and better all around .
08-11-2015, 07:11 PM
#6
Pro
Thread Starter
Save the money by the time your done with reconditioning the stock rods both big and small ends .You'll have spent around 450.0 to 500.00 add another 170.00 if you put in better rod bolts and still have the stock heavy rods for 250.00 to 400.00 more you can get a set of Woosners or Cerullo's .There lighter and better all around .
I got into a complete rebuild while I was searching for an exhaust leak. Digging further and further led to discovering bad head ceramics, that led to seeing how poor the pistons were, that led to seeing a groove in a rod bearing, then at that point i figured why not just replace the main bearings too.
In the time between my posts, I ordered new bushings. Going to the shop once I get them. Then I can finally start building!
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08-12-2015, 03:27 AM
#9
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08-12-2015, 07:18 PM
#10
08-19-2015, 01:44 PM
#12
Rennlist Member
If it turns out that you need to resize the big end of the rod, and you want to go for a bit more $$, now would be the time to put in ARP rod bolts...The stock ones are probably sufficient, unless there is one that is cracked or chipped. This would be an upgrade and probably will incur more costs. Talk with your engine builder/machinist. If you are a fanatic, you might want to get the rods magnafluxed...LOL!
08-19-2015, 03:33 PM
#13
Pro
Thread Starter
If it turns out that you need to resize the big end of the rod, and you want to go for a bit more $$, now would be the time to put in ARP rod bolts...The stock ones are probably sufficient, unless there is one that is cracked or chipped. This would be an upgrade and probably will incur more costs. Talk with your engine builder/machinist. If you are a fanatic, you might want to get the rods magnafluxed...LOL!
08-19-2015, 06:18 PM
#14
