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question about '86 piston
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Posted by: kiesta00

I was wondering why the 86 piston does not have an intake "window"...the piston only had 2 little holes. why is that? thx

Keith

Posted by: Eddiesanders250

i was wondering the same thing

Posted by: GPracer2500

I'm pretty sure those little holes are lubrication holes for the exhaust bridge.

Posted by: C-LEIGH RACING

If you have a Wiseco piston, you can cut a intake window in it if you like, just cut it in up high & champher the edege real well on the inside & outside.
The edeges of the cut in window will have little hair like cracks you cant see with you eyes & need sanding down to remove them or else cracks will open up like a crack spot on a windshield.
Neil

Posted by: kiesta00

Would this help performance any? or is it really worth the work...lol

Posted by: C-LEIGH RACING

I would say to some extent yes, far as a hp # I have no idea.

What you get from the hole, as the piston travels & uncovers the transfer ports you will get a gas/oil charge flow from the crankcase up through the hole into the reed chamber & up through the rear boost port.
This flow helps cool the inside roof of the piston as well as lubes the upper rod, wrist pin & bearing.
This piston mod is just one of the many little things that add up when building a high performance engine.
Just like baking a piston, you cant see what it does but it adds up in the end.
Neil

Posted by: kiesta00

cool thanks for the info...how the hell do you know so much about engines? lol

Posted by: C-LEIGH RACING

I'm 55 years old & had something to do with some type of racing sence I was 14, old dirt track cars, 2 cycle karts, flat track motorcycles, & sence 1986 4 wheelers most of them being TRX250Rs.
Everything I do at my shop is like someone working in a lab. Spent more time measuring, looking up part numbers, matching up parts, & trying different things out & testing than Dale Earnhart probably spent driving that #3 race car, probably not though, reason, dont know how many hour he set in the seat.

Was born & living in the North Carolina mountains untill 14 when my dad was killed & moved east.
If I has stayed in the mountains I more than likely would be on a Nascar team right now & that didnt happen, so all I have left is to leave my mark on the ATV world.
Neil

Posted by: jon370r

I've never herd of baking a piston. What does that accomplish?

Posted by: C-LEIGH RACING

quote:
Originally posted by jon370r
I've never herd of baking a piston. What does that accomplish?

Do you know whats happening on a fresh engine & your breaking it in ?? what is happening on the inside ??
Neil

Posted by: jon370r

The new piston and rings expand and any high spots are being worn down to fit the bore by the proper crosshatching of the cylinder walls. What else? I'm interested now.

Posted by: Rich250RRacer

quote:
Originally posted by kiesta00
I was wondering why the 86 piston does not have an intake "window"...the piston only had 2 little holes. why is that? thx

Keith

To answer your original question, the 86 piston does not have the intake window, it has an arch cut-away on the skirt. The 87 and newer motors use a bridged intake which allows a full-skirted piston, but requires an intake window. Because the 85-86 cylinders do not have a bridged intake, they should have the 85-86 piston. One reason being there is a VERY slim chance that the full-skirted piston could "cock" or snag on the large intake port of the 85-86 cylinder on the downward stroke. And this is MORE likely if a larger piston-to-wall clearance is run. With the arch cut-away, there is no chance of the skirt catching the port, since there is no skirt TO catch.

Posted by: kiesta00

thanks rich for that explanation...that helped me understand things better

Posted by: C-LEIGH RACING

quote:
Originally posted by jon370r
The new piston and rings expand and any high spots are being worn down to fit the bore by the proper crosshatching of the cylinder walls. What else? I'm interested now.

For the most part that is right.

Each time you start the fresh engine for a break in cycle it needs to be gotten real hot. That heat, is heat setting those new parts to the shape it will run in, more so on the piston itself.
Baking the piston before hand in a sence is removing some of the stress put into the piston from machining. Gives the piston a little break while doing the breaking in process.

Some builders say baking the piston before putting the engine together takes away the break in process.
I'm still going do the break in steps though.
Neil

Posted by: jon370r

I never thought of a forged piston needing to be stress relieved but like you said earlier every little trick can add up in the end. I will have to try it. At what temp. and for how long?

Posted by: C-LEIGH RACING

Some builders will bake them 5 - 10 - 15 times at different temps working up to around 400* at the last & about an hour each time. I only do 4 times at 2 hours each.
Neil