Piston slap? Reliability..?

[Jankenshank]

so i have a 6bolt block which has been bored .020" over bringing the bore to 85.5mm by the previous owner
ross 8.5-1 pistons, stock 1g rods and a eagle crank,

so my blocks at the machine shop atm, the shop called me up today to inform me that my block is done and ready to go and that my actual bore is 85.7mm (shop didn't bore it, just a hone)

so i'm in a dilemma,

should i say screw it plonk the pistons i have in again and deal with the slap.... but i believe this will cause issues with reliability... any insight?

should i bore it to 86mm and get another set of pistons and plonk it in there....

there's a budget (500 a month towards it)
and a time limit, needs to be ready and broken in for spring IA (April 11th)


for the engine est HP400 and it will be running 9krpm

any and all responses welcome!

cheers
janken!

 

[DSM_PWR]

Do things right the 1st time ...

Have them check the PTW ratio, piston slap is not fun

 

[Jankenshank]

i will be doing the assembling, the machine shop is just used for the hone and deck,

PTW will be about .3mm since it .2mm over on the bore than what it should be.

 

[the_elite]

What kind of hone are they using? And Do you have a set of gauges and give me he exact P2W clearence. It all depands on how bad that is. Piston slap can be fine, it all depands on how much P2W.

 

[BogusSVO]

heres a trick... call to some machineshops in your area... find one that can Knurl your pistons.. then uoi can file the knurl down till you get the P2W clearance that you want

 

[Jankenshank]

ok... just got back from the machine shop.... my bore is 3.368" so its .002" out

my piston measured 3.360" but it was cold so we stuck it next to a fire then measured 30 mins later... measured 3.364 which leaves a P2W of .004"

not too much at all and its the exact clearance that ross pistons call for.

thanks for the replys!

this can be locked!

 

[#40Fan]

Your engine will be cold, pistons will be cold.... .008" is going to be way too much.

 

[bastarddsm]

heres a trick... call to some machineshops in your area... find one that can Knurl your pistons.. then uoi can file the knurl down till you get the P2W clearance that you want

Ewww Aids infected band-aide.

 

[Jankenshank]

Your engine will be cold, pistons will be cold.... .008" is going to be way too much.

yep, i'm just going to let it idle until at operating temp... shouldn't hurt it... i hope

Ewww Aids infected band-aide.

^wtf? please explain.

 

[BogusSVO]

well it has worked in engines for years.. but if you have the cash to lay out for a new set of forged pistons fine....

or if you can get your hands on a block thats std bore.. great... but the OP is wanting to use what he has.

OP.. if you knurl them, then fit them , you may be able to send them off if you want and get the skirts slick coated that will add about .0005 to .001 to the piston dia.

 

[quiksilver20004]

What is the end gap measurement if you put your rings down in the cylinders? And you also have to remember that pistons are not round when they are cold, they are actually more of an oval.

 

[Jankenshank]

ill get the end gap measurements when i can, wont have time over the next few days..... working 8-10 through Wednesday...

 

[bastarddsm]

well it has worked in engines for years.. but if you have the cash to lay out for a new set of forged pistons fine....

or if you can get your hands on a block thats std bore.. great... but the OP is wanting to use what he has.

OP.. if you knurl them, then fit them , you may be able to send them off if you want and get the skirts slick coated that will add about .0005 to .001 to the piston dia.

Knurling pistons died in the 50's. Thats an old timers trick to get more life out of junk parts. Pulling shit like that on a dsm is the exact reason dsm's are labled as temperamental piles of elephant dung.

What actually happens when you knurl a piston is the metal is displaced so that there all small islands of material taller than the basemetal, but they are surrounded by holes lower than the base metal. Its kinda like if you took a flat piece of clay and pinched a peak in it. It's just like that, but all over your pistons.

In the end you can take up your clearance with it, but your surface area is now about 30% of what it used to, that means it will wear quickly and be loose in no time.

 

[Rob10_99]

What's ring gap have to do with PTW?
Sounds like you will be ok with those clearances yeah, sounded WAY off at the first post =)

 

[Jankenshank]

What's ring gap have to do with PTW?
Sounds like you will be ok with those clearances yeah, sounded WAY off at the first post =)

i wondered the same thing about Ring gap correlating with P2W clearance....
figured he knew something i didn't.

.002" is nothing really.

 

[#40Fan]

I am sure that he/she wasn't suggesting the ring gap had anything to do with P2W clearance, but more along the lines if the rings will seal enough with the big cylinder.

You talked about the pistons having a .004" P2W clearance after the pistons were warmed up. What I would do, and I am sure what Ross would recommend, is to put both pistons and block in a warm room for (who knows) amount of time and then measure the P2W. Let both the block and pistons reach an equal internal temp and then do the measuring. If you have the .004" afterwards, then I would call it good.

 

[Rob10_99]

I assume all the mfg's use standard measurements at 68*F, ANSI standards right?

 

[400hp93talon]

I would assume so!