Wiseco Piston and Hybrid Ceramic Bearings from Dominant Saws for 372XP

[blsnelling]

I big thank you goes out to Dominant Saws. They have sent me one of their Wiseco 372 pistons and a set of hybrid ceramic bearings. I plan to put the piston in my "new" 372. I don't remember if I put ceramic bearings in this saw or not. If not, the bearings will be going in this saw as well. I haven't yet made any measurements, but here are pics of the items.

 

[Jacob J.]

Interesting Brad- did they send you the parts to demo? I've been eyeballing those pistons for a while now.

 

[Jacob J.]

BTW- it says "50cc" on the box, so don't build your engine too big.

 

[Locust Cutter]

Interesting...

 

[RedneckChainsawRepair]

BTW- it says "50cc" on the box, so don't build your engine too big.

noticed that too. cc instead of mm

 

[blsnelling]

Interesting Brad- did they send you the parts to demo? I've been eyeballing those pistons for a while now.

Yes. Do you know what P to C clearance should be? I'm hoping to avoid the scuffing I encountered with the 066 Wiseco piston I tested from Baileys.

 

[MustangMike]

I ran ceramic bearings in my bike crank, but I think you will be encountering a few more RPMs!!!

 

[Rx7man]

Nice looking stuff!.. cost?

 

[blsnelling]

I ran ceramic bearings in my bike crank, but I think you will be encountering a few more RPMs!!!

I have run ceramic bearings in a couple other saws with good results. It's critical to use those with black Si3n4 balls, not the white ZrO2 balls. The ZrO2 balls will fail within a tank or two. I have run hybrid ceramic bearings with Si3n4 balls for several years in a high RPM 346XP with no issues at all. I also have them in my piped 390XP.

 

[Locust Cutter]

Soooo..... If you found a basket case 390xp and were going to rebuild it, would you spend the extra$$$ to split the cases and use these bearings, even if the original bearings were still good (under the mantra of do it right the first time)?

 

[blsnelling]

Ceramic bearings are not needed for 99.9% of saws. I've been told by a race saw builder that their only real advantage over a standard bearing is that they don't require break-in. For most saws, your just as well off to go with an inexpensive set of quality bearings with C3 clearance ratings. With that said, I can tell you that these bearings are SMOOOOOOOOOTH!!! I didn't know the bearing were coming with the piston, and couldn't readily see what the balls were made of. Once I spun them, I figured they had to be ceramic. I then found the note in the package stating that they were. A set of bearings like this will run you about $100.

 

[gunnusmc03]

Nice looking stuff!.. cost?

Piston is $150

 

[Rx7man]

I figured it would be expensive.. but I will say it looks very nicely finished.. you get what you pay for.

Back in my Rx7 days, I put about $10,000 into an engine, best of everything went into it, additional dowel pins, apex seals that cost $200 each (x6), and lots and lots of porting... I didn't own it long enough to push it to it's limits by far.. but it made 375 RWHP at just 11 PSI of boost... and a buddy of mine with a very similar engine did push his to the limits.. he got 875 RWHP at 48 PSI on race gas from 1.3L.. he also daily drove it (at about 500 rwhp pump gas) and it lived for about 50,000 miles.. The castings gave out and cracked at that point.

Power, Reliablility, Cost. Pick 2!

 

[blsnelling]

The box states clearance should be only .0010". That just doesn't seem like enough to me, especially when we're dealing with a forged piston that will expand significantly more than a stock cast piston. @Jacob J. or @leeha , what kind of clearance have you guys seen work well with Wiseco pistons?

 

[mdavlee]

.003" would be better. Probably have to let it warm up good before burying it in wood if it's truly .001"

 

[blsnelling]

I've got a nasty old 372 jug setting out in the garage with most of it's fins broken off. It has a great bore though. I think I'll go throw it in there and see what it is.

 

[strtspdlx]

Less then .003 from my dirt bike days is what I was always told. Anymore and wiseco pistons had an annoying piston slap.


Regards-Carlo

 

[blsnelling]

Using a snap gauge and micrometer, the bore measures 1.969" and the piston measures 1.967" at the bottom, center of the skirt. Using a feeler gauge, it has a tight .002" clearance at the bottom of the skirt, exactly the same as a new Meteor 50mm piston for a 044. The big difference is in the diameter at the crown. The Meteor piston measures 1.961" and the Wiseco measures 1.955", leaving a lot more room for expansion where the piston gets the hottest. I also noticed that the Wiseco is .002" smaller, 1.965", across the diagonal of the skirt corners. The Meteor is consistent at 1.967" at all points around the skirts.

According to what I found online, the minimum ring gap should be .008"-.010". I've got .011".

Hopefully my 372 cylinder is no smaller, and hopefully just a hair bigger.

 

[Jacob J.]

Yes. Do you know what P to C clearance should be? I'm hoping to avoid the scuffing I encountered with the 066 Wiseco piston I tested from Baileys.

I'm running a Bailey's Wiseco piston in one of my 372s...the gap I had averaged around 0.0020-0.0025" or so with my old Snap-on feeler gauges. I'm running it in a later "B" cylinder, which usually have a little more clearance than an A cylinder. Even with as small a bore as 50mm- I don't think I would run it as tight as 0.0010".

 

[blsnelling]

Another interesting measurement was that the crown is 0.150" thick at the edge. Most pistons are only 0.135" or less. The popup is an additional .038" tall. Lots of room there for additional popup making.