Wiseco piston failure!

[bryanwess2000]

Well I determined the cause of my engine failure. My newly acquired
starcraft had a recently rebuilt 90hp merc 3cyl. that blew the #2 piston
the second time I took it out. It caught the top piston ring in the exhaust
port. All I did initially was pull the powerhead off and pull the crankshaft
assembly to inspect the bores. Today after I got back from my first splash
of the starcraft with the merc V135 I decided to investigate the 90hp.
My first thought was the bores were too tight for the pistons as they
mic 3.375-3.376 and the wisecos' need extra clearance. I ruled that out
when the piston skirts mic'ed at 3.365, plenty of clearance. Also there
was no scuffing on the piston. It turns out the locator pins' hole was
machined in the wrong spot, about .009-.010 off compared to the other
2 pistons. Between that and the piston ring groove being a few thousandths
wider than the other two pistons it allowed the ring to move around to
the point the ring gap was in the exhaust port and bam engine failure.

I wonder if wiseco will at least send me a new piston kit, I kind of doubt
it considering I'm not the original purchaser. I know mistakes happen in
production machining but the locator pin is a very critical part of a 2 stroke
piston and should have strict quality control. I know if I do any rebuilds
in the future, which I plan to, I'll be thoroughly inspecting the pistons as
well as any other critical components.

 

[trendsetter240]

Re: Wiseco piston failure!

Just curious who did the rebuild; was it the PO that did it himself or was it done at an authorized dealer?

Also what series were the pistons? There should be a number stamped on the head of the piston.

 

[sschefer]

Re: Wiseco piston failure!

That's not something Wiesco is known for. Just out of curiosity, check the part number against the others. Sounds to me like it's the wrong piston all together. I could understand if there was one small defect but machining it all wrong doesn't sound like a defect to me it sounds like the wrong part. It could be that it was a overstock set bought on eBay and the seller (and buyer) didn't know any better.

What can and does happen is if there is a problem with a complete set of matched pistons, Wiesco just sends you a new matched set and doesn't ask for the bad set back. Sometimes those bad sets get back out in circulation via eBay or other online stores.

 

[bryanwess2000]

Re: Wiseco piston failure!

The original owner had the motor rebuilt then gave the boat to his son
who got stationed in pensacola, who in turn sold it to the reserve officer
I bought it from. The trailer had a IL tag with a 2007 registration so my
guess is it was rebuilt 2007 or earlier.

All the pistons part #'s are the same 3020ps with KD under the part #.
All other dimensions are the same except locator pin position, and the
locator pin is still in its hole. I could tell by looking at the locator pin that
it was off compared to the other two pistons.

I can see how it would be easy to miss in a production machining setting
by a $10/hr machine operator. Thats what I started out as before I got
into a real job shop and learned a whole lot about what I didn't know.
I learned more in three mos. in the job shop than I did in 4 years at the
production shop. After 3 yrs and 3 work related surgeries I changed careers.
I digress, anyway unless each piston is checked at the factory by the
operator, doubtful considering how fast the cycle time wound be on a small
aluminum part, it would have a slim chance of being caught by the QC
inspector unless it was a large batch. They basically just pull parts randomly
to check and unless one of the ones they pull is out of spec. the bad parts
aren't found until assembly or later. This includes ISO 9000 certified companys
I know most of the machine operators at the shop I worked at didn't take
pride in their work and produced costly bad parts that weren't found until
assembly. This led to signing a slip that followed the parts through out
the various stages of machining.When that didn't work I and other supervisors
started having to check each 10th part in addition to our other responsibilities
so you can guess what happened. Alot of those 10th parts didn't get checked
. This was at a large modern shop that's iso 9000 certified and guarantees
1 million cycles on their actuators. They also happen to be part of a large
conglomerate. Sorry for the long winded response I just wanted to illustrate
how bad parts from a company can make it to you. I'm not bashing wiseco
I'm sure they would have exchanged the piston had it been caught by the
builder. I don't blame the machine operator I know how hard it is to keep
up with a CNC running small aluminum parts.

 

[Dukedog]

Re: Wiseco piston failure!

My experience with tha Wiseco's is its all in tha machine work and break in. Got ta leave a minumum of .008 tolerance contrary ta what a lot of folks say. They are a forged piston instead of cast. Break-in is slow with a lot of up n down rpm and motor temps (temps are VERY important) with a little extra oil ('bout 32 ta 1) for about tha first 20 ta 30 gallons of fuel. Machine work and break-in not right, they WILL stick.................If all is done right they will run and run and run and run and run etc. etc. etc. unless like ya say, tha machining of tha part is supect......JMO

 

[Faztbullet]

Re: Wiseco piston failure!

3020 is old stock Wiseco's, must have been setting on rebuilders shelf for a while, the new numbers are 3120's. As for stock engines I use only cast pistons unless I dont have a option, and if I use a Wiseco I add about .002 extra to bore for expansion. Funny thing is ring gap should not be that close to a port,usually ring gaps are 1/4-1/2 inch away from ports. I had a customer years ago bring me a late 80's 80 hp 3 cylinder that popped 3 times in a 2 week period, found out fellow that he was getting pistons from was giving him 2.4 V-6 pistons and they when hanging in the ports.

 

[sschefer]

Re: Wiseco piston failure!

Bryanwess - I agree completely with your analogies even in a iso 9000 shop. Stuff happens. One of the hardest things for small or hobby engine builders like myself is knowing if your parts are bad or not. Rarely do we have anything else to compare. I think this is a valuable lesson to be put into the notebook for future reference... Mine will read something like... Check the pistons!!!! Thanks for sharing this with us.