Wossner piston question

[hotrodaj_2]

I have a 240 bbk with a LA Sleeve. LA Sleeve sells Wossner brand pistons so that is what I have rebuilt with. My problem is that I keep getting major scratches on cylinder and piston. Im now on my last bore and pulled head today to check it and I got scratches again. One day riding is all it takes. I thought maybe I caused the previous problems with jetting being wrong and a air leak or two but I got everything perfect this time. Engine is as fat as it can be and still run clean and I leaked it down many times, she is sealed up tight. My machinist knows what he's doing so bore is correct, I double check now. Sleeve is deburred and cleaned well. He has opened up the bore another .001 to fix problem but he should'nt have to. Has anyone had problems with Wossner pistons growing more than the tolerance they suggest? Any other ideas would be great.

 

[slickerthanyou]

First I heard of that! Are the rod bearings within spec?

 

[slickerthanyou]

I remember that wossner gives you actual piston size, as where wiesco -prox tell you what size to make the bore, However they all say what clearances should be! A builder should always measure the piston and go from there IMO.

 

[hotrodaj_2]

Rod bearing might be causing it, idk. Thats a good suggestion. I'm out of ideas myself. I did alot of research because this has started costing me alot of money in rebuilds. The scratches and their placement suggest its running hot or tolerance is to tight. That is hard for me to accept because im anal when it comes to building engines. The first and second problem could have been assembler error, but not the third and forth. Do you gotta split case to check rod bearing or can it be done assembled?

 

[slickerthanyou]

assembled no problem!

Found this on google-
Wossner Piston Official | Piston Installation

 

[hotrodaj_2]

I always heat cycle. Uni filter with alum. air box, cleaned every ride. I talked about tolerances with machinest alot. were left scratching our heads so he opened her up another .001 because were out of ideas.

 

[Blaaster]

After rebuilds do you heat cycle before you break in?

What air cleaner is your choice, is it cleaned often?

Are you warming up the motor before you fang it?

What oil and ratio do you use and do you add extra oil for break in?

 

[slickerthanyou]

 

[hotrodaj_2]

Thanks slick. That post does have a little info I did'nt know. The piston is measured before coating is applyed. Must factor in the .00047 coating thickness. I'm not sure if that was done but I dont really think a coating .00047 thick, then its gone shortly after riding would cause major scratches like it has.

 

[hotrodaj_2]

Ya, I warm her up before riding. I do coat everthing inside engine during assembly, I do not ad more oil to fuel for break-in. I use 32:1 yamalube

 

[Blaaster]

Are the scratches random or are they confined to the same area?

 

[hotrodaj_2]

Minor scratches on 30 percent of piston but the major ones look like there on the four corners. Research tells me the big scratches on four spots are from to much heat or to tight of a tolerance, I forget which one right now. I gotta refresh my memory. Either way, it's hard to beleive with all my preporation and adjustments that the problem dos'nt change.

 

[Blaaster]

Four point sieze indications of piston expanding too quickly in the bore.

Uneven warm up, not enough warm up, tolerences a tad too tight, the list goes on.

 

[Blaaster]

I tend to think that the scoring is happening early in the heat cycling process.

Progressive heat cycles could help avoid the problem.

First cycle to half heat, secong to 3/4 and third to 7/8 and final 2 two full heat.

Then on rides make sure that the motor is fully warmed up before riding.

 

[Blaaster]

The piston expands unevenly in the bore because of the extra meat surrounding the wrist pin area.

On a fresh rebuild it is extremly important that the motor be warmed up fully before hard work.

 

[hotrodaj_2]

I hear you loud and clear Blaaster. Maybe I mad a mistake early on, lean, airleak, not warm it up enough. I cant beleive its warm up now. I have covered that. I cant warm it up any slower or more. I know thats a cause but something strange is going on, it could be a little tight on tolerance but we have checked that. This is why my original question was if anyone has had problems with Wossner pistons growing to much or to fast, if not than I'm still lost as to why this is happening over and over.

 

[joeak47]

I have a 240 bbk with a LA Sleeve. LA Sleeve sells Wossner brand pistons so that is what I have rebuilt with. My problem is that I keep getting major scratches on cylinder and piston. Im now on my last bore and pulled head today to check it and I got scratches again. One day riding is all it takes. I thought maybe I caused the previous problems with jetting being wrong and a air leak or two but I got everything perfect this time. Engine is as fat as it can be and still run clean and I leaked it down many times, she is sealed up tight. My machinist knows what he's doing so bore is correct, I double check now. Sleeve is deburred and cleaned well. He has opened up the bore another .001 to fix problem but he should'nt have to. Has anyone had problems with Wossner pistons growing more than the tolerance they suggest? Any other ideas would be great.

Can you post a picture of the piston and cylinder for us to see?
What is the piston to cylinder clearance are you running? These are forged pistons (I know you know that),so they require a RELIGIOUS warm up before riding. Not a quick 3 minutes while you put your helmet on. Do you check to see that your bore is round and strait with no taper? I'm not trying to sound redundant.

I was running a wiseco forged piston earlier this summer that was properly clearanced (.0025),and in the 105 degree ambient temperature outside, It swelled up a bit more from the heat and got scuffed. Still ran good though.
Engine tempuratures (cylinder and head) went as high as 375 degrees after a very hard,and long run. This was verified with my infrared thermometer.

I have since went back to a cast piston because they retain they're shape when hot and don't expand as much as a forged piston. This was verified a few days later when it was 106 degrees ambient tempurature and I did the same long ,and hard run,and noticed about a 10-15 degree drop in cylinder and head tempurature (also checked with ifrared),then did a tear-down that evening to confirm the cylinder and piston condition. The cast piston still looked like new. I'm not saying to go with a cast piston,even though that is what I prefer,I am saying to warm up that cylinder RELIGIOUSLY before riding.

 

[hotrodaj_2]

I have tryed to break-in engine properly. That might be the problem but when I research it I get a dozen different breakin procedures. I just watched Ken Oconnor's video on breakin and I guess I'll use that one. Ken has always done me right and I trust he really knows what he's doing. I will keep ur break-in procedure in mind Blaaster. Thanks for help. I might have used a wrong break-in from the dozen choices but I'm still not 100% convinced. Maybe Wiseco pistons are not as sensitive. Idk

 

[Blaaster]

I apologise for rabbiting on, it is my way of prying info to help fix a problem.

You could try jetting on the rich side the keep the piston crown temperature lower.

Sometimes a borderline AFR can cause the upper piston to expand more quickly than the bore can, which can make the area around the wrist pin grab the bore.

 

[joeak47]

Remember that the forging process compresses the aluminum into a smaller area,leaving the molecules smashed closer together. When they get excited (heated up) they want to expand a much larger amount compared to a comparable cast component.

When I say warm up before riding I don't mean to let it just sit there and idle, I mean to start your bike,get your gear on,get on your bike and blip the throttle quite a few times to bring up the cylinder tempurature.
Now put your un-gloved hand on the cylinder and FEEL. Make sure it gets "too hot to touch",put your glove back on,then go ride. A luke warm cylinder with a forged piston is asking for trouble.