Piston Decentigrated

[blazer200]

Has anyone ever had a problem with propelled marine pistons?I just put my 2.4 back together and with less than 2 hours on it #6 piston self destructed for no reason,motor was not hot and I was only turning 4000 rpm.:(

[baja200merk]

injected motor?

[blazer200]

Yep,laser motor

[RSM]

Where exactly did it break? Can you post any pic's, also isn't Propelled just a dealer? Is it a PRO piston, and why was it replaced to begin with?

[blazer200]

Correct,pro marine piston purchased from propelled marine,I bought the motor blown and put new pistons,rings,bearings ect.As far as where it broke i've only pulled the heads off and it is broken from the ring grooves up.I'm not sure abou the skirt yet.
I'll post pics if i can,my camera is acting stupid.

[RSM]

Do you know why it blew the first time and was it the same hole? Usually for a piston to break under those conditions would seem like a clearance problem in the rotating assembly or a week spot in the casting of the piston. PRO pistons seem to have a good reputation as far as a Hyperutectic cast piston goes. Hard to tell without pic's but I am curious to see more because I to have a PRO-MAX that has PRO pistons. Is your motor stock?

[blazer200]

It's pretty much stock except for boyesen reeds and drystacked exhaust.I'll try to get some pictures up after i get the motor apart AGAIN so you can see the entire piston.I'm not sure why it blew the first time,it was blown when i got it.

The block is not the original block,it needed to much work (sleeves) and I got this block from Mercthunder.The #6 did have a sleeve in it clearance was .003 when i put the motor together the first time and it had the correct rings.

[us1]

.003..........it probably seized.

[baja200merk]

.003..........it probably seized.
i dono bout mercs but my johnny wit wisecos is set at .075 thats a huge difference :eek:

kevin :confused:

[150aintenuff]

.075???????????????????????????maybe .0075..... and yes .003 thousandths is way to tight... 6-9 thousanths is more like it for clearences

[Rickracer]

There's one of your problems. Correct me if I'm wrong, but clearance on a cast piston should be at least .001 for every inch of bore, a little more for a motor that's going to be run hard, and considerably more for a forged piston motor. On top of that, you may have an injector problem that caused the demise of the first piston. If you did not determine what caused the original problem, you only duplicated it. I'd definitely have the injectors flow tested, especially after burning down 2 pistons in the same hole. :cool:

[ChrisXS2003]

The rule of thumb is 0.001 per inch of bore...that's per side right? Measured on the diameter, it’s roughly 0.007 diametral clearance on a 3.500 inch bore?

0.003 on the diameter is only 0.0015 actual piston clearance

C

[Rickracer]

Now that's for a cast piston in a steel bore. Wiseco recommends .005 to .0065 for their forged pistons, most knowledgeable builders will either go .0075 or more, or do a very extensive break-in. I like .008 on my X-Flow OMC motors with Wisecos, but since I am not turning over 7500 with a V-4 anymore, I like the Pro Powers much better now anyway. :cool:

[baja200merk]

Wiseco recommends .005 to .0065 for their forged pistons, most knowledgeable builders will either go .0075 or more

i think it was racer who said weiseco recomends .005 so they get more buissiness :eek: :p

NPARTIN- I THOUGHT MY PISTONS SEEMED A BIT LOOSE :eek:

kevin