Undersize Piston

[Tuneup 1,433]

I long for the teenage days when micrometers were costly and B&S and Tecumseh engines always went together and ran perfectly fine with Dad's old tools. Today, I can afford micrometers, and they're even cheap and accurate. Measured the piston from the kit on eBay and measured my old carbon cut piston and the new is .010 smaller! The bore and original piston meet original specs, by golly! Letter off to the supplier to convince them my engine is not already 010. Oh, for the days of ignorance. She'd be back together, smoking and perhaps slapping nicely...

[Phatboy 565]

Hahaha 

[tractorhogg 611]

12 minutes ago, Tuneup said:

I long for the teenage days when micrometers were costly and B&S and Tecumseh engines always went together and ran perfectly fine with Dad's old tools. Today, I can afford micrometers, and they're even cheap and accurate. Measured the piston from the kit on eBay and measured my old carbon cut piston and the new is .010 smaller! The bore and original piston meet original specs, by golly! Letter off to the supplier to convince them my engine is not already 010. Oh, for the days of ignorance. She'd be back together, smoking and perhaps slapping nicely...

I must be confused or reading it wrong, (happens to me), If your piston and bore are standard, how could a new piston be .010 smaller than standard, wouldn't it be bigger, if it was smaller that doesn't even make sense, that means you would need a .020 over to fit standard by their measurements? Have things gone this bad?

[Tuneup 1,433]

Nah - original piston with the usual carbon streaking meets manual's specs at 3.363. Bore measures a stock 3.374. The new is 3.348. Almost tempted to use the original but the top ring is so exposed. We'll see what the supplier says. Yeah, I dropped it all and laughed. I'm at the age where these kind of things are simply funny. If his quality is this bad, an .010 over would almost make it stock. No eBay complaints so I guess no one's measuring or I'm just, as usual, the lucky one.

[tractorhogg 611]

20 minutes ago, Tuneup said:

Nah - original piston with the usual carbon streaking meets manual's specs at 3.363. Bore measures a stock 3.374. The new is 3.348. Almost tempted to use the original but the top ring is so exposed. We'll see what the supplier says. Yeah, I dropped it all and laughed. I'm at the age where these kind of things are simply funny. If his quality is this bad, an .010 over would almost make it stock. No eBay complaints so I guess no one's measuring or I'm just, as usual, the lucky one.

This guy you bought it from is probably only a middle man for chinese products, could be shrinkage cause in transit, lol or conversion from metric to SAE sizes, like our shoes, pants, and coats.

[Tuneup 1,433]

That leaves the engine still in pieces on the bench and nothing but a frame and a transaxle attached to two tires remaining of what was once a C-125. It will all come together one of these days, hopefully before the grass starts to grow.

[tractorhogg 611]

I hear ya, Maybe the guy will start checking what he buys and resells, he should have been doing that in the first place

[JAinVA 4,619]

Tuneup,

        I know you can't tell us who sold you the parts but my question is if that person is the one that we all seem to get parts from?I don't expect to get Kohler OEM parts

from him but wow.The last crank bearings I got from him were made in Japan.Sure that for the price they would have come from China.JAinVA

[Tuneup 1,433]

Let's see how he responds. The box with piston contains a sheet on the ring positioning that states Taiwan. No other indication of source. All but the compression top ring gap to spec. Top ring needs some filing.

[Howie 885]

Could be someone in the manufacturing facility mis-read mic or dropped it and calibration was off. I worked in a cold heading screw manufacturing plant

for 45 1/2 years and they eventually provide digital mic's to try to do away with errors in reading the tool. Were checked for accuracy quite frequently

and logged. Some people tend to squeeze the mic more and some use a lighter touch which can effect the reading by a few tenths.Now .010 is more

than a little. A supplier probably not going to check a lot of these unless they start to get a lot of returns. I know the supplier I buy a lot of parts off of

would replace it but have dealt with them for 20 years or so. Will see how good his customer service is with how he responds.

 

David  

[Tuneup 1,433]

Hi Howie,

 

Yes, training today is even more crucial than in the past. We seem to be hiring less skilled today - all that are available. I am in the electronic calibration business and the standards have been reduced significantly. They may know what tool is needed bu not how to use it and in this business, overtightening is $1000s in damage.

Well, the supplier responded back very quickly so, good on him!

 

According to them, it's my bad. I was measuring the piston just above the pin according to the manual but this late piston is designed to be measured at the base of the skirt and it is right on the button for spec at that point. Figures. So, it's all good. His reply:

 

I think you are measuring piston at the wrist pin area. That is correct for a car piston but not an air cooled engine. The piston you removed is an older style Kohler and has straighter sides where as the very late style have a steep taper and are measured at the bottom of the skirt. If you measure there 90 degrees from the wrist pin holes it should measure 3.3675 to 3.3695. These are made by the same manufacturer Kohler is currently using to supply parts so I doubt it is incorrect. We have never seen a piston made wrong and we've sold or used about 20,000. All the latest style pistons from Kohler have large taper in fact the magnum 18 and 20 pistons are .100 smaller at top so must be measured at bottom of skirt. If you don't like kit just return and we will refund money but I know all the current suppliers of these have the steep taper so you'll get the same from anyone else. If you find the bottom of skirt off let me know as anyone can make a mistake but since these are cnc'd there would be lots of them not just one and we haven't had any issues. Thank you

 

[WHX?? 48,077]

Seems like an honest reply anyhow?

[Tuneup 1,433]

Yes, better than IT support! I recall he is located in Ohio so that's a good thing.