How to R&R pistons and Balance Rods
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How to R&R pistons and Balance Rods
How to R&R pistons and Balance Rods
The used rods and pistons, the pistons are being replaced due to cracked and broken ring lands.
I start off by marking the front of the rod with a center punch
Next is to find the proper sized press pieces to press out the wrist pins.
Due to the pressures used to press out the wrist pin, care must be used, the piston itself can bust sending pieces of it flying that can and will cause injury.
After the pistons have been pressed off, and the small end inspected for scoring, the rods need to be numbered on both the rod and end cap.
Now the rod and caps can be split and cleaned, I use a glass beader to remove all the grime
Once that is done I spray them down with a good brake cleaner and blow them dry
Chase the rod bolt threads with a nut to remove any dust left from the glass beading.
Now to match the rods back with the caps
Install the rod nuts.
Now the rods are clean and assembled, they can be balanced. Start off by weighing all the small ends
The weight will be matched to the lightest one.
Once the small ends are matched, weigh the overall weight of each rod, and match the overall weight by removing material from the bottom of the rod.
Now that is done, it is time to match the weights of the pistons WITH OUT the wrist pin installed.
Then weight match the wrist pins.
Now that all the weights are with in 1/10 a gram the pistons can be hung back on the connecting rods. The small ends must be heated so the wrist pin can slip through it.
This must be done very quickly so the wrist pin is fully in place before the small end of the rod contracts around the wrist pin holding it in place.
The used rods and pistons, the pistons are being replaced due to cracked and broken ring lands.
I start off by marking the front of the rod with a center punch
Next is to find the proper sized press pieces to press out the wrist pins.
Due to the pressures used to press out the wrist pin, care must be used, the piston itself can bust sending pieces of it flying that can and will cause injury.
After the pistons have been pressed off, and the small end inspected for scoring, the rods need to be numbered on both the rod and end cap.
Now the rod and caps can be split and cleaned, I use a glass beader to remove all the grime
Once that is done I spray them down with a good brake cleaner and blow them dry
Chase the rod bolt threads with a nut to remove any dust left from the glass beading.
Now to match the rods back with the caps
Install the rod nuts.
Now the rods are clean and assembled, they can be balanced. Start off by weighing all the small ends
The weight will be matched to the lightest one.
Once the small ends are matched, weigh the overall weight of each rod, and match the overall weight by removing material from the bottom of the rod.
Now that is done, it is time to match the weights of the pistons WITH OUT the wrist pin installed.
Then weight match the wrist pins.
Now that all the weights are with in 1/10 a gram the pistons can be hung back on the connecting rods. The small ends must be heated so the wrist pin can slip through it.
This must be done very quickly so the wrist pin is fully in place before the small end of the rod contracts around the wrist pin holding it in place.
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So can you explain for somebody who has never seen an engine apart in person: What moves relative to what with the piston/rod/wrist pin? I guess I always assumed the wrist pin stayed stationary relative to the piston, and the rod kind of rotated around on the pin, but based on your heating description, that doesn't seem right. Also, on some other engine you were working on, the wrist pins were held in with clips, suggesting that they just kind of floated and everything was free to rotate. This seems like the method with the least friction...
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Skidude... You are on the rigt track.
There are 2 basic types of pistons, Press fit and full floating.
With press fit pistons, the wrist pin is gripped by the small end of the con rod.
Most engines were assembled this way years back. Floating pistons was for hind end racers.
But over the past 15 years or so, the OEs have been going to the full floating style.
The 1.8l has a full floating set up from the factory
With this set up style, the wrist pis is free to rotate in the rod and piston. The wrist pin is held in place some style of wire lock or sprio lock.
There are 2 basic types of pistons, Press fit and full floating.
With press fit pistons, the wrist pin is gripped by the small end of the con rod.
Most engines were assembled this way years back. Floating pistons was for hind end racers.
But over the past 15 years or so, the OEs have been going to the full floating style.
The 1.8l has a full floating set up from the factory
With this set up style, the wrist pis is free to rotate in the rod and piston. The wrist pin is held in place some style of wire lock or sprio lock.
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When a person keeps the same crank but gets new pistons and rods same as the above procedure is showing, would this be advertised at a shop as "balance rotating assembly" ?
I'm assuming the crank doesnt need to be touched and that once I follow your procedures here I have DIY balanced my rotating assembly myself ??
I'm assuming the crank doesnt need to be touched and that once I follow your procedures here I have DIY balanced my rotating assembly myself ??
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If I'm paying a shop to balance the rotating assembly are they basically assembling the bottom end of my motor for me as well? Can you explain the process? Also I hear conflicting views on whether to include the clutch / flywheel as part that assembly?
Thanks
Thanks
#9
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Balancing the rotating assembly, has nothing to do with building the bottom end/short block.
First all the pistons will be brought to the same weight, commonly within .5g high to low
Then the small end of the rods will be weight matched, then the big end or overall weight will be done.
Next the crank will be put on a spin blancer, and brought into balance. By removing weight from the counter balance weights of the crank, or in some ultra lightweight rod/piston combos weight will be added to the crank.
This would be a "Basic" balance
Now, some go a bit further, I normally do, and add the H-balancer, the flywheel and pressure plate.
Now the flywheel and H-bal is installed on the crank, and spun up.
Any weight removed will come off the flywheel.
Now the Pressure plate will be added, and spun up again.
Now the machinist running the balancer machine, will rotate the pressure plate on the flywheel untill the balance gets close, then index the PP to the flywheel.
once that is done, any weight that needs removed will come off the pressure plate, normally 2g or less.
Now with done, it can all be cleaned again, and short block assembly can start.
First all the pistons will be brought to the same weight, commonly within .5g high to low
Then the small end of the rods will be weight matched, then the big end or overall weight will be done.
Next the crank will be put on a spin blancer, and brought into balance. By removing weight from the counter balance weights of the crank, or in some ultra lightweight rod/piston combos weight will be added to the crank.
This would be a "Basic" balance
Now, some go a bit further, I normally do, and add the H-balancer, the flywheel and pressure plate.
Now the flywheel and H-bal is installed on the crank, and spun up.
Any weight removed will come off the flywheel.
Now the Pressure plate will be added, and spun up again.
Now the machinist running the balancer machine, will rotate the pressure plate on the flywheel untill the balance gets close, then index the PP to the flywheel.
once that is done, any weight that needs removed will come off the pressure plate, normally 2g or less.
Now with done, it can all be cleaned again, and short block assembly can start.
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Thank you for the explanation. I was under the impression that they assembled the block then balanced some how.
How necessary is this step if one is replacing pistons and rods and balancing them as described above? I'll be keeping to the stock rev limit if that matters .
How necessary is this step if one is replacing pistons and rods and balancing them as described above? I'll be keeping to the stock rev limit if that matters .
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I personally recommend on any rebuild to atleast weight match the rods and pistons.
Most 4 cyl cranks are normmaly close from the factory.
The closer you get to a "perfect balance" the better and the smoother the engine will run.
Now most aftermarket, forged, pistons and rods are generally fairly close.
OE replacement cast pistons I have seen as far off as 6g
If you havent read these threads, you will see what I found with new parts right out the box.
https://www.miataturbo.net/engine-performance-56/first-look-supertech-pistons-1-8l-dohc-65235/
https://www.miataturbo.net/engine-performance-56/first-look-manley-h-beam-connecting-rods-65527/
Most 4 cyl cranks are normmaly close from the factory.
The closer you get to a "perfect balance" the better and the smoother the engine will run.
Now most aftermarket, forged, pistons and rods are generally fairly close.
OE replacement cast pistons I have seen as far off as 6g
If you havent read these threads, you will see what I found with new parts right out the box.
https://www.miataturbo.net/engine-performance-56/first-look-supertech-pistons-1-8l-dohc-65235/
https://www.miataturbo.net/engine-performance-56/first-look-manley-h-beam-connecting-rods-65527/
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