HPJunkie

I am rebuildiing my 502 and have new JE forged blower pistons. The instructions say 004-005 piston to wall and plus up to 002 -003 extra for marine use. I dont think a too loose is good either is it? Any experience here? Thanks Greg

kennyo

Do exactly what JE says. My machinist had it set up and bored for regular use and I called JE and told them what I was running( cold block no t-stat for a procharger) We had to go back and open it up. People want to build these tight like car engines and that's why they blow 'em up.

Reed Jensen

Marine engines need more clearance between the piston and cylinder wall because of two things.
1. The pistons are under a greater heat load and run hotter, hence, they are expanded more. Remember, aluminum expands a lot with heat.
2. Marine blocks run cold and therefore don't expand as much as automotive blocks. So you need .002 more clearance so the the piston doesn't scuff in the bores.

88Fountain

iTrader: (1)

I run Mahle pistons in my NA 540's. The piston to wall clearance is .0065. I run a crossover with no thermostat.

stevesxm

with all due respect Reed, i think you are wrong on both counts. in an apples to apples comparison, the internal thermodynamics of a marine engine and an automotive engine are precisely the same. and if you are running your block cold you wouldn't need larger clearences... you would need tighter clearences... not to mention that overcooling the block is a dumb thing to do from a metallurgical stand point anyway. piston to wall clearences are simply a function of the material the piston is made out of , its total mass and how much cam grind the manufacturer puts in it. running big clearences is no magic speed secret... its just a way to guarantee that you get bad ring life and average sealing. if you want the motor to make power and live, you run it at normal operating temeratures with as tight a piston to wall that the specific piston you are using will tolerate.

Pismo10

It has nothing to do with speed, it is survival of the engine. Pistons are hotter and will expand more so you need more space when building at room temp.

KNOT-RIGHT

Solid Advice given here!

Make sure your machinist also follows the ring manufactures
honning procedure as well. Torque plates, ring gap, and
RA finish.

LMAC

Tighter cylinder wall clearances in a marine application is a one way ticket to "lock up".
Different manufacturers require differnt clearances for their alloys and shape of piston. Depending on application, the rule of thumb is to add .001+ for differances in expansion.

gg10

Piston to wall is a function of bore size, stevesxm is on another planet, h2o temp in high hp is low because of the volume of h2o required in block and difficulty of regulating temp.Piston to wall should also consider use, big diff if your are going to run wot for extended periods or cruise at part throttle.

GoCiggie31

HP,
I am running the srp (JE) 4032. (Std 4.466 wtih .064 =4.530)
The SRP chart calls for .0030/.0035 @ .500 up from btm skirt.
(cold water pickup marine app may require an additional .002-.004)

We went with from skirt up .003.5, then .004 then .005 close to bottom ring; kinda a taper in towards rings to minimize piston slap cold.
I'll let ya know how it works on my very heavy deep v twins.

p.s.did above on last 502 and still running after 200+ hrs on single deep v.