Help with decking or not?

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Just know that if the cylinders are all within a .005-.006"" deck height range, the total static CR variation cylinder-to-cylinder will be around 0.1 point based on that factor alone. If the head chambers are equalized to get rid of that variation, then that is a pretty good CR variation to live with for a street build; IMHO, you don't have to go crazy with this parameter for most uses, you just need to know it is not way out. There's going to be some other cylinder-to-cylinder variations that you can't do much about, like intake and exhaust port variations and such.
 
Mountain, mole hill. The block needs squared up period. Otherwise you will have a different compression on each cylinder. And do mock it up while at the machine shop. We did mine with a brand new 408 Scat assembly and had three rods that needed the big end sized and had to purchase a new set of OVER SIZE main bearings because the set in the kit had ZERO clearance. Fix all now or pay latter.
 
Donnie514 said:
Mountain, mole hill. The block needs squared up period. Otherwise you will have a different compression on each cylinder. And do mock it up while at the machine shop. We did mine with a brand new 408 Scat assembly and had three rods that needed the big end sized and had to purchase a new set of OVER SIZE main bearings because the set in the kit had ZERO clearance. Fix all now or pay latter.
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Did u purchase your kit balanced? And yes i am having it squared up and most likey will go to mock up once he calls me
 
I really do not know how far off it was on balance, must of been minor cause they only charged me a hundred bucks, but the main bearing clearance freaked me out. you would most likely be OK. I am a perfectionist. Cleanliness and clearances are right at the top and yes blue printing a motor is checking and correcting ALL.
 
Donnie514 said:
I really do not know how far off it was on balance, must of been minor cause they only charged me a hundred bucks, but the main bearing clearance freaked me out. you would most likely be OK. I am a perfectionist. Cleanliness and clearances are right at the top and yes blue printing a motor is checking and correcting ALL.
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Yeah of course i feel the same i was going to have my machinist double check it. As for the clearances when i mock it up ill see but this is my first performance build so i want it done right and close to perfect qs possible as i am building it
 
Be aware that there is tolerance in the weighing of parts, especially so in separating the big end small end weights for computing bobweight; that particular part of the weighing process is very sensitive, and is prone to errors in equipment AND technique. So, a local machinist may achieve a better or worse tolerance, and it may be just as much in the opposite direction as what comes from SCAT or another mfr. If the local equipment is inaccurate or the techniques poor, one may think one is improving balance, but may very well just be moving it around.
 
nm9stheham said:
Be aware that there is tolerance in the weighing of parts, especially so in separating the big end small end weights for computing bobweight; that particular part of the weighing process is very sensitive, and is prone to errors in equipment AND technique. So, a local machinist may achieve a better or worse tolerance, and it may be just as much in the opposite direction as what comes from SCAT or another mfr. If the local equipment is inaccurate or the techniques poor, one may think one is improving balance, but may very well just be moving it around.
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What you say is pretty much correct. That's why you take your stuff to a EXCELLANT machine shop. Every one is different, and every machine is different. Your feel is different than mine. That's why using a feelers gauge is tricky. To adjust a valve lash at .020 you should use a .19 and a .21 gauge. And don't forget I stressed cleanliness. Dawn dish soap, bottle brushes, WD40, garden hose, white paper towels, and white rags. Also keep a spray7 bottle of water with a shot of ammonia in it and a can of brake kleen with spout for little touch up cleaning.
 
005=006 is close enough
you have crank grinders trying to a .010 grind and getting the indexes a little off and/or the big ends getting a different amount of short when rebuilt
to get them right you almost have to bush the rods then finish to correct length and or set up all the big ends the same which is more of a PITA
even if you equalize the end chambers on stock heads when milling it takes hand work to make them all the same-- a lot more work and you have to equalize on the biggest chamber
this is not a "blueprint" or heads up type superstock build where that extra effort is more critical
 
Most guys who want things "perfect" would cringe if they actually knew how far off a "balance" job can be without any real world consequences.

While we tend to expect to see or hear a difference most engines will happily run hundreds of thousands of miles without any issues with an inbalance that would drive some folks crazy if they only knew.

balancing holes ? - Speed Talk
 
I've seen many 440's torn done for the first time to be bored and other basic machine work. They find out the replacement piston are a lot lighter than what they had originally and needs to be rebalance. Only to find out that the stock piston were 20-30 grams different on most of them and the crank wasn't balanced that closely either. But other than that, the engine ran great with no noticeable vibrations or issues you would expect with that much of a mismatch from the factory.
 
Krooser said:
Most guys who want things "perfect" would cringe if they actually knew how far off a "balance" job can be without any real world consequences.

While we tend to expect to see or hear a difference most engines will happily run hundreds of thousands of miles without any issues with an inbalance that would drive some folks crazy if they only knew.

balancing holes ? - Speed Talk
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Thank you for that article link, Krooser. Just reading the 1st page helped me on one thing.... looks like very few in the industry, if any, know the stock factory bobweights on various cranks. I've been looking for that info for a while, with no luck so far.

For the OP: The point I wanted to bring out in the balance tolerances is that if a shop says that the SCAT job was found to be '5 grams off' or something like that, then is still is a question of who is closest to 'perfect'. So when I read that kind of report, I always mentally question it. It is good to have it checked in case of a slip up, and in particular, if it is an internal balance crank set, to see if your TC/flextplate or flywheel, and damper are themselves in balance. I have to wonder how many well done, internally balanced crank sets are thrown off by not checking those external parts... I am raising my hand, as in 'guilty as charged' LOL!

Donnie514 said:
Mountain, mole hill. The block needs squared up period. Otherwise you will have a different compression on each cylinder. And do mock it up while at the machine shop. We did mine with a brand new 408 Scat assembly and had three rods that needed the big end sized and had to purchase a new set of OVER SIZE main bearings because the set in the kit had ZERO clearance. Fix all now or pay latter.
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Hey Donnie, this info of big ends out of size brings up memory of a thread here about a year back, where one of the professional shop operators here had found that some of the aftermarket rods would go out of round after a certain number of installations of the rod cap and torquing of the rod bolts to spec. Not sure what brand it was, or how often it occurred or maybe was one-off situation, but that was a eye-catching outcome.
 
Krooser said:
Most guys who want things "perfect" would cringe if they actually knew how far off a "balance" job can be without any real world consequences.

While we tend to expect to see or hear a difference most engines will happily run hundreds of thousands of miles without any issues with an inbalance that would drive some folks crazy if they only knew.

balancing holes ? - Speed Talk
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Yes and if those same guys wanting perfection knew how far off everything was from the factory and how many millions of miles engines racked up in all makes and models, they would fall out.

That said, there's nothing wrong with blueprinting everything to where it "should be". Makes the engine more accurate all the way up.
 
Also RRR, it' not uncommon for many race assemblies to be overbalanced by 2% or more. So for and engine like a big block with a possible bobweigh if 1800-1900 grams, that's almost 50 grams over the actual bobweigh. As I mentioned previously and you also said, many would fall out if they knew how "far" the balance is out from the factory and they still run hundreds of thousands of miles on the street and strip just fine. So the Scat stuff is probably as good as most factory balance jobs.
 
RustyRatRod said:
Yes and if those same guys wanting perfection knew how far off everything was from the factory and how many millions of miles engines racked up in all makes and models, they would fall out.

That said, there's nothing wrong with blueprinting everything to where it "should be". Makes the engine more accurate all the way up.
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LOL so true. If you've ever had an untouched Chrysler crank on the balancer and looked at how far off it was and didn't shake...most guys would be stunned.
 
CNC-Dude said:
Also RRR, it' not uncommon for many race assemblies to be overbalanced by 2% or more. So for and engine like a big block with a possible bobweigh if 1800-1900 grams, that's almost 50 grams over the actual bobweigh. As I mentioned previously and you also said, many would fall out if they knew how "far" the balance is out from the factory and they still run hundreds of thousands of miles on the street and strip just fine. So the Scat stuff is probably as good as most factory balance jobs.
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I only did that much over balance when the RPM was 8500 or more. Even a 1% over balance is a bunch.

You also have to remember when you over balance like that you can end up with a low speed out of balance issue that may be in an RPM range that the engine can shake itself to death if you stay in that RPM.

An example is a 500CC two stroke. They are as much as 50% over balance IIRC (been awhile since I've done one) and they SHOULD shake a bit at idle. If they don't...it's a short life for them.
 
yellow rose said:
I only did that much over balance when the RPM was 8500 or more. Even a 1% over balance is a bunch.

You also have to remember when you over balance like that you can end up with a low speed out of balance issue that may be in an RPM range that the engine can shake itself to death if you stay in that RPM.

An example is a 500CC two stroke. They are as much as 50% over balance IIRC (been awhile since I've done one) and they SHOULD shake a bit at idle. If they don't...it's a short life for them.
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That's true, we only did a full 2% on Comp Eliminator stuff and circle track engines that operated in those RPM ranges.
 
Wow I got a lot of remarks on the balance job on a Scat rotating assembly that was a minor deal. The BIG surprise was the zero clearance on the mains. There crank and the in closed with the kit main bearings. do not just "assume" anything is correct.
Donnie
 
Donnie514 said:
Wow I got a lot of remarks on the balance job on a Scat rotating assembly that was a minor deal. The BIG surprise was the zero clearance on the mains. There crank and the in closed with the kit main bearings. do not just "assume" anything is correct.
Donnie
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That's correct, I've seen really good stuff from Scat and other offshore companies, but I also have seen what you are experiencing now as well. More consistently from Scat more than anything is the balance not being as close as it could/should be for our standards. The journal sizes being out of round and tapered is not uncommon, but In my experiences with them is probably around 15%-20% of the time. One other issue I had with one of their cranks was in a Chevy 400 where they drilled a lightening hole through one of the rod journal's too close to the bearing surface and made the journal collapse almost immediately on startup. But I would check all aspects of the crank and not just the obvious things.
 
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