Wiseco Piston Break In Process

G DANE

Commander
Joined
Nov 24, 2001
Messages
2,476
Re: Wiseco Piston Break In Process

If the tolerances you mention is correct, the forged pistons will be a lot quieter than the casted. All motors should iddle at least 5 mins before running wot, thats what owner manual says too. Congratulations with your rebuild, well done !!!
 

Mark_VTfisherman

Lieutenant
Joined
Nov 29, 2008
Messages
1,486
Re: Wiseco Piston Break In Process

Huh? An interference fit would mean they would be pressed together? :eek: And thirty five thousandth's clearance is spark plug gap territory....

Hi- just read your response, and looked at mine again. I apparently missed zeros after the decimal; however, I don't know why I even responded. I posted that at 11:20pm and I can't even explain my answer: .0005 is not as tight as .00035 :redface:

It's 10:30 pm, and I am going to bed now before I say something dumb tonight, too
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: Wiseco Piston Break In Process

WELL, My 2 cents: I have rebuilt a number of different brands of 2 cycle outboards and if possible, I always use Wiseco. They are amazingly well made and worth every buck you pay for them.

NOW: from necessity, when the owner picks-up his rig, I take it out on the water with him. With only about 5 minutes running time, It is necessary for me to use full throttle to set timing. HOWEVER: Once timing is checked and confirmed as correct, the engine no longer sees full throttle. I caution the owner to not exceed 3/4 throttle or 3500 RPM until at least two 6 gal tanks of double oil mix has been run through the engine. On the larger engines, this works out to somewhere around 4 hours. Say, 1,000,000 cycles

I have never had a return or complaint, and all my personal engines run "like a top."

ALL outboard engine pistons are cam ground because the cooling water cools the cylinder unevenly. This also causes the piston skirt to heat and expand unevenly. Thus, when the engine warms up, the piston becomes more nearly circular and it and the cylinder now match in shape. Engine tolerances vary from manufacturer to manufacturer. For example, while OMC uses .005 clearance, Force uses .002. AND total wear allowed in the cylinder for taper, out of round, or oversize is .005 on OMC and .002 on Force. THUS if your Force engine has only .002 wear, it is necessary to bore .010 over. AND- the listed clearance is hot clearance--wiggle a cold piston in a cold cylinder--amazing how much slop there is, especially at the crown which gets way more heat than the skirt.

Since racing applications or higher power modifications usually result in more cylinder pressure and higher temperatures, and since the aluminum piston expands to a greater degree than the steel cylinder liner, these applications require a bit more clearance. Engine runs like crap until it warms up but racing engines are not meant to run cool or slow.

NOW: My personal opinion--- 3000 RPM works out to 180,000 cycles per hour. If rings aint seated and it aint broke in by then, it aint never gunna be.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Wiseco Piston Break In Process

Well, just had a good long conversation with a tech at Wiseco followed by a good long conversation with the Machinist that bored my block and sold me the pistons.

The conclusion: forged OEM replacement pistons should be broken in following the standard OEM break in process. (With a few bits of advice from both the Wiseco tech and the Machinist)

Both advised to follow the standard break in process with the following additional comments.


Advice from Wiseco Tech:

1. Use standard 2-stroke oil, not synthetic, at the double rate (25:1) during the break in process. Synthetic oil can lead to glazing of the cylinder walls before the rings have set.

2. Avoid extended idle periods after the initial 10 - 20 minute startup of the motor.

3. Throughout the life of the pistons, always provide a 5 minute warm up period at or near idle before running WOT.


So you never got to the Marine Manager? What sort of Marine background does the tech have?
 
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