OMC Piston - vs - Wiseco Piston... and why?

[Jmorrell588]

I am trying to decide which Piston to go with for my 90hp Evinrude VRO Crossflow. <br />I have heard both good and bad about Wiseco. I talked to a person today who has told that I should go with Wiseco Piston. He had said that they are stronger pistons since they are forged. Unlike the OMC Piston which is cast. So, which one is the best for my Motor? Also was told that I have to warm up longer for Wiseco Pistons. <br /><br /> Jimmy

 

[Hooty]

Re: OMC Piston - vs - Wiseco Piston... and why?

You've got another piston option. They're Pro Power Pistons. They're cast, not forged but are a lot tougher than OEM pistons. It might not be so with the newer ones but Wiseco's used to require more piston to cylinder clearance due to expansion. <br />Dhadley will probably have the last word for ya though.<br /><br />c/6<br /><br />Hooty

 

[Walker]

Re: OMC Piston - vs - Wiseco Piston... and why?

I've been using Wiseco pistons for 10 years and have never had a problem with clearances. I'm fairly certain that my machinist cuts my cylinders to OMC specs. Wiseco's are a lot cheaper than OMC especially if you can fine your pistons on Ebay. If you want to try to find some on Ebay get your piston number and cross match it to all models that it fits because the seller might list it for another application. I just bought one for a V6 crossflow that was selling as an 88SPL.

 

[Dhadley]

Re: OMC Piston - vs - Wiseco Piston... and why?

The Wiseco will work as good as or better in your motor. It is a forged piston and very strong. Do not lug the motor. Make sure your motor is capeable of 5800 rpm with an average load. This is very important. <br /><br />The series part number you want is 3173. If you are boring to .020 then the piston number is 3173P2. .030 over is 3173P3, .044 is 3173P4, .064 over is 3173P6. 3173PS is standard. <br /><br />You must determine what caused your motor to be damaged and fix the cause in order to avoid a repeat. A damaged piston is the result, not a cause. <br /><br />Good luck!

 

[clanton]

Re: OMC Piston - vs - Wiseco Piston... and why?

I think Walker said the key word, CHEAPER. Nearly every machine shop around here gives the wiescos more clearance. If I did a standard engine I would use a OMC or pro piston. We used a wiesco piston in a 250 Kawasaki short tracker about 30 years ago that worked great,and a Kawasaki won the North/South Championship using a wiesco piston, 1969 or 70.

 

[Dhadley]

Re: OMC Piston - vs - Wiseco Piston... and why?

Any 307_ series and all the 31 series Wiseco use the standard OE finish bore size. And they are anodized.

 

[Hooty]

Re: OMC Piston - vs - Wiseco Piston... and why?

Yo,<br />Dhadley.<br />What's magic about 5800rpms and Wiseco pistons??<br /><br />c/6<br /><br />Hooty

 

[Jmorrell588]

Re: OMC Piston - vs - Wiseco Piston... and why?

Mr. Dhadley, Claytone, Walker and Hooty, I think that what caused the piston problem was the carbon build-up. However, I wonder if the carbon build-up was the reason (Which there was a lot of carbon in that whole) for the piston to break apart at the tip and chip off scouring the cylinder. Now I did notice that there was a slight color distortion. But I cannot be sure of this since all the tips of the cylinders are coated with carbon. Also, when I pulled the plug out of that port, ( the bad port) there was smoke coming out of it (like on a cold day when you can see your breath) but not out of the other ports when I pulled the plug out of them.<br /> Now you had said "Lug", would that mean to run the motor under stress ie., Towing a boat, running 1/4 trottle while viewing the ladies, lugging your woman around the lake or lugging all those waverunners that ran over cause they messed up the fishing and ruined the peace and quite?<br /> Do note, that some of the things mention above are not true. But on a more serious side, what would lugging fall under in your terms?<br /> I am leaning more towards Wiseco by the minute. Now the part about 5,800 rpms, is that to mean that the high end must reach that rpm?<br /><br /> Jimmy

 

[Dhadley]

Re: OMC Piston - vs - Wiseco Piston... and why?

There's no magic. I'll bet that Jimmys motor was only capeable of top rpm's in the low 5000 range. That contributes to the coking (carbon build up) that caused the damage. That's lugging the motor no matter if you run wide open or 1/4 throttle. If the motor (crossflow in this case) can turn in the 5800 range (average load) it runs freely throughout the entire rpm range. The combustion temps come down and the coking problem is greatly reduced or eliminated.<br /><br />Jimmy, you are very correct about towing other boats, skiers, heavy loads etc. Thats why folks change to a smaller pitch prop to do so. It reduces the (temporary) stress on the motor. Thats why we always stress to prop out your rig with an average load. <br /><br />If you decide to go with a cast piston I would highly recommend the Vertex piston. You still want the 5800 to avoid doing this again.<br /><br />Unless you need the pratice!

 

[Hooty]

Re: OMC Piston - vs - Wiseco Piston... and why?

Are 4 cylinder engines more susceptible to lugging and as a results coking than 6 cylinder engines??<br /><br />c/6<br /><br />Hooty

 

[Forktail]

Re: OMC Piston - vs - Wiseco Piston... and why?

Either cast or forged pistons will work fine. The bottom line is that cast pistons (Vertex) expand much less under extreme temperatures than forged pistons (Wiseco). Cold and hot siezures are less likely with a cast piston, but forged pistons are usually stronger.<br /><br />Wiseco usually includes the piston/cylinder clearance specifications in the box, along with the piston. Not every Wiseco has the same clearance. Cast pistons can be bought as balanced and matched sets, sometimes even from OEM. A good cast piston is very strong.<br /><br />I would go with the Vertex myself.

 

[Dhadley]

Re: OMC Piston - vs - Wiseco Piston... and why?

Any motor that is lugged is more likely to coke up or promote carbon than a motor that is not being lugged. No matter what pistons are in it.<br /><br />Forktail -- glad to hear you like the Vertex. How long have you been using them? In which motors?