Need some advice with my piston swap.

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Dragonbat13

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OK, I did some searching but I need a little specifics.

I have a 2-6" Starret outside mic. All I can get access to at this point is some cheap telescopic gauges from harbor freight to get the inside measurments of the bores. Will these two tools be reliable enough to make an hone or overbore decision?

What I have is a .040 magnum engine with smogger pistons. I bought some Scat I beam rods since those with be used with any engine I build. I want to replace the smogger pistons with KB 107's, use moly coated rings, and have the machine shop hone for the rings and deck the block to zero.

My worry is the difference in the smogger pistons and the KB 107 pistons, which I dont have yet. I dont want to order .040 pistons if I either need to rebore or find another block.

Does anybody know the average diameter of the KB 107 pistons? What is the maximum out of round taper and bore diameter for a KB 107 when using moly rings.

Engine is gonna be a street engine on 92 octane.
 
Better off having the block checked by your machine shop for taper, etc. Bore gauge is going to be much more reliable in this case. Then choose your pistons. Do not buy until they check the block.

Most pistons now have the clearance built in. This means that if they're .040 pistons and they need .003 clearance, they're machined to .037 & with them being cnc now, they're all within 1/2 thou at most.
 
So, you're wanting to do a hone job and slap in a set of new pistons, correct? That won't work with KB hypereutectics. They have very specific clearances that if not met will cause the skirts to separate from the piston tops. Read about it here www.uempistons.com/installation_instructions/kb_installation.pdf Do yourself a favor and save some bucks on tools you really won't need more than once or twice. Verify the current bore size. Order a set of pistons .020" larger than that. When the new pistons arrive take them, the block, and the installation instructions to a GOOD machine shop. The only way to get the clearances you need for happy KBs is with a new hole...
 
grumpuscreature said:
So, you're wanting to do a hone job and slap in a set of new pistons, correct? That won't work with KB hypereutectics. They have very specific clearances that if not met will cause the skirts to separate from the piston tops. Read about it here www.uempistons.com/installation_instructions/kb_installation.pdf Do yourself a favor and save some bucks on tools you really won't need more than once or twice. Verify the current bore size. Order a set of pistons .020" larger than that. When the new pistons arrive take them, the block, and the installation instructions to a GOOD machine shop. The only way to get the clearances you need for happy KBs is with a new hole...
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Thats my thinking also, which unless I can find a KB 107 in .050 over, ill have to go .060 over.

Whats the thoughts on .060 over magnum engines?
 
Actually, the clearances with the KB pistons that are critical are the top ring gaps. You can run more than the allotted piston to wall clearance just fine. You may have some piston slap when cold, but a little ***** slap never hurt anybody. If you want to run a hyper piston and not have to worry about custom file fitting rings, run the Speed Pros.
 
As the others said, talk to a good machine shop. Magnums have pretty thin castings and you may be in trouble with a .060 overbore. It is best to have them check it first then buy your pistons. You should have it balanced also. With different rods and pistons you really don't know where you're at for weight. tmm
 
Im reading where it costs under a hundred dollars on average to sonic check a block. Im bringing it to the machine shop and see whats up.
 
I'm running KB 107s in my 360, good pistons, engine runs really nicely. But I had to ring it twice! the first time I didn't quite follow KB's instructions closely enough and gapped the top ring too tight. After the short block was together I realized my mistake and had to take it apart again. Min for me was 26 thou, I gapped to 28 just to be safe. They are good pistons but you have to really follow the instructions!
 
Using telescoping gauges is a real PITA, but it can be done. Personally, I'd spend a few bucks and have the machine shop measure the bores and compare to the specs for the pistons you want to run. You'll know real quick where you stand.

If you plan to do this more than occasionally, consider investing in a dial bore gauge. This one should be just fine for automotive inspection... http://www.shars.com/products/view/2196/26quot_Dial_Bore_Gauge
 
X2 on letting the machine shop do it. That's not an area to mess up on.

Also x2 on the kb instructions. Much more so then other piston brands. That's why I went with the speed pro.
 
Let me throw this out,

THey got some badger B290 used 40 over pistons on ebay right now for 100 dollars. They look OK. This mag block is really something I dont feel comfortable putting serious money into. I am thinking about buying the pistons (they are the same as the dished ones in it right now, but flat tops. Throwing that junk onto the stock unsized rods, putting a cheap rebuild kit in it. Not balancing it, and seeing how long it takes to blow up. I mean, I got the scat rods, and those could wait for a better block and maybe some stroker peices.

This would be a cheap, OMG I cant believe he did that engine. But the compression would be around 8.9 to one. And it would get my car on the road.

Sound like a crazy plan?

I hate the fact that some moron bored a perfectly good mag block over to .040.
 
Dragonbat13 said:
Let me throw this out,

THey got some badger B290 used 40 over pistons on ebay right now for 100 dollars. They look OK. This mag block is really something I dont feel comfortable putting serious money into. I am thinking about buying the pistons (they are the same as the dished ones in it right now, but flat tops. Throwing that junk onto the stock unsized rods, putting a cheap rebuild kit in it. Not balancing it, and seeing how long it takes to blow up. I mean, I got the scat rods, and those could wait for a better block and maybe some stroker peices.

This would be a cheap, OMG I cant believe he did that engine. But the compression would be around 8.9 to one. And it would get my car on the road.

Sound like a crazy plan?

I hate the fact that some moron bored a perfectly good mag block over to .040.
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Yes it does,no offense to you. A screw up of major proportions, delivered on your purchase.Your proposed idea,a waste of cash. You will be unhappy, with the slam together results. J.M.O..
If you are this far invested,check out a set of forged Icon pistons,hone it.. J.M.O.
 
Make sure you look at the compression distance on those badger pistons versus the dished pistons. Most of the time, the compression distance on the flat tops is shorter, resulting in the same compression as the dish. You don't buy pistons based on looks.
 
I checked that compression deck out. It is the same. I am simply loosing the dish.

I would spend the extra coin on forged pistons. My future plans were to go to eddy RPM heads. IIRC forged pistons require a higher skirt to wall clearance. I was considering getting forged pistons that would give me a flat top, work with the current .040 with a rehone and give me excellent quench with the RPM heads.

Can I get pistons that would allow this?

ANd the bores on the engine right now look really good, no thrust side wear.

I a very sorry for all these questions, I got stuck with a motor that was not something of choice, and finding mag 5.9 engines down in south louisian are hard.

I really, REALLY appreciate all the help. I already got a chart with all the piston compression heights I have so far, and plan on handing that out as a refrence.

Thank you very much for all the help.
 
I am sure LKQ has an outlet close to you. They sell 5.9 magnum engines with a 6 month warranty in the 300 dollar range all day long here.
 
RustyRatRod said:
Make sure you look at the compression distance on those badger pistons versus the dished pistons. Most of the time, the compression distance on the flat tops is shorter, resulting in the same compression as the dish. You don't buy pistons based on looks.
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Really ? Crap I bought the Mahle pistons cause they looked so cute with the coating and all , the colour combo just looked so good had to have them . So far it's worked out well , 12,000 miles and I don't burn a drop of oil between changes , just checked the oil level and with 2500 miles level is still 1/16th of an inch from full mark and relatively clean .
Pulling the heads today , will take some pics , see how much wear or damage pistons /block have .
 
Good decision on getting a dial bore gauge. I spent around $70.00 on one from ebag last year. It's great for checking blocks before you buy them for bore size, taper, etc.
 
Im gonna spend a little more and get the .0001 Shars listed above. I already got a 2-6" outside, Graduated burrett, 1" outside, Dial indicator and a bunch of Telescoping gauges. A 2-6" dial bore gauge would be a good next purchase.
 
Dragonbat13 said:
My ole lady posted that. I didnt know about it.
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She probably got a kick out of you runnin everybody around in circles like you always do. That's why I really don't reply much anymore.
 
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