Incorrect Bore Job?

[400exrider707]

Ok my buddy has been having some bad luck with his foreman 450. He sucked some water a while back through a crank case vent. We tore it completely down, got new bottom end off of ebay for it and put it back together. Got it all back together and of course when he got it running again it was smoking and making all sorts of racket still as he reused almost all stock parts in the top end against my advice. He was on quite a tight budget at the time though. Well fast forward 6 months. He has a good job now but not a lot of time to work on toys. Well he brings this foreman in to get the top end looked at and get a new piston. He gets a wiseco piston and overbore. He also got new valve seals, but again I believe stock valves were re-used. Everything did look OK though considering the age. Well all is well for a little while then it starts burning oil. A lot of oil. He gets pretty concerned. It still runs OK, but just using a lot of oil. Finally does a leakdown test with terrible results. I tell him its possible the rings didn't seat well, pull the head off and check them out. Pulls the head and first thing he notices is the ring gaps are all lined up!

Here is his first letter to me this morning:

"Hey,

So I took the Foreman apart again on Saturday expecting to replace the rings, and the piston is shot… The skirt on one side of the piston is worn really badly. The metal from the side of the piston actually was pushed into one of the grooves for the lower oil scraper… It must have gotten pretty hot because you can see on the inside of the piston where there are brown spots from the heat. It was only on one side of the piston/cylinder though, the other side looked ok. Of course the cylinder wall is scored in that spot pretty bad too, so it will need to be re-bored regardless. I think it was bored incorrectly. Any thoughts?"

Then I ask for pics and get these, not the best but you can kind of see whats going on, I'll try and get better pics later, any ideas here?

http://i39.photobucket.com/albums/e166/400exrider707/piston.jpg

http://i39.photobucket.com/albums/e166/400exrider707/piston2.jpg

[yernkie]

We pulled a piston out of a Rancher last week that looked just liek that. The problem was that the crank/rod bearing went bad (I believe lack of oil) and the rod allowed the piston too much movement.

[Jason Hall]

If the connecting rod Is bent, It can cause the rings to line up. I have never had this happen to me personally, but have heard It from a old deisel mechanic. He told me that the bent rod will actually make the piston twist slightly In the bore, causing the rings to spin In the ring grooves. Once the compression finds the easy way through, the rings will line up & stay lined up. The skirt looks like the engine got hot, or the piston Is probly just shot from previously having water In the oil.

[400exrider707]

Originally posted by Jason Hall
If the connecting rod Is bent, It can cause the rings to line up. I have never had this happen to me personally, but have heard It from a old deisel mechanic. He told me that the bent rod will actually make the piston twist slightly In the bore, causing the rings to spin In the ring grooves. Once the compression finds the easy way through, the rings will line up & stay lined up. The skirt looks like the engine got hot, or the piston Is probly just shot from previously having water In the oil.

This is a brand new piston with less than 5 hours run time on it.

[chad502ex]

suspecting a bottom end bore centerline issues is possible and should be considered,..

there are some other possible reasons..

Being that this was a wiseco piston and wiseco doesn't produce pistons with forced wrist pin oilers,,, and,,,,, manually free fit their wrist pin,,,,, a binded wrist pin could prevent necessary piston wobble. A binded wrist pin could seize the side skirt to one side causing excessive heat through rubbing. How hard was the wrist pin to remove from the piston? was there wrist pin piston binding?

improper piston to cylinder clearances when bored could cause the piston to bind when the piston fully expands.

cross-hatching is 'said' to rotate the rings during operation to prevent hot-spotting while being filed into the fresh bore

[JasonP]

These all been said but I agree...
Lack of oil.
Improper bore, clearances to tight. Did he send the piston out with the cylinder to the machine shop when having it bored?
bent rod or tight wrist pin on con rod.
Reving the **** out of the engine or overheating.

[400exrider707]

Piston was ordered and in the hands of the same place that did the boring. Here is what my buddy said after I told him some possible explanations:

The wrist pin was somewhat difficult to remove come to think of it. I had to tap it out with a small deep socket and hammer. I don’t know if the actual pivoting of the piston was restricted, but it definitely didn’t slide right out by hand.

So sounds like perhaps a lack of oil to the wrist pin. I dont get this... if all wiseco's did this, they would be out of business wouldn't you think? I ran a wiseco for 2 seasons in my 400ex and never had a problem like this....

also if this is the case, why would the rings be lined up perfectly? This work was done at a pretty reputable shop and they gave him typical BS answers as to why this happened and also made sure to tell him it was definitely not a problem caused by the boring of the cylinder...:rolleyes:

the guy at the shop said that the damage done to that piston could not have been done by incorrect bore, and that it looked like a lack of oil. He gave me a bunch of reasons why it may have happened, all speculation of course. One of which is that I ran regular automotive motor oil in it, rather than 4-cycle atv/motorcycle oil. To be honest I never knew there was a difference until yesterday. Apparently the automotive oil doesn’t have the necessary properties for both engine and transmission lubrication in a wheeler. He said he has seen several atv engines destroyed that way.

[jeremy_283]

is there metal to metal transfer? or melting? if not then no lack of oil

[chad502ex]

Originally posted by 400exrider707
Apparently the automotive oil doesn’t have the necessary properties for both engine and transmission lubrication in a wheeler. He said he has seen several atv engines destroyed that way. [/B]

oh my... too much advertisement bottle reading imo.

[400exrider707]

Originally posted by chad502ex
oh my... too much advertisement bottle reading imo.

My thoughts exactly. The guy at the shop that did the bore job told my buddy this and I laughed. Sure an ATV specific oil may have some better additives in it, but c'mon an automotive oil destroying a motor in less than 5 minutes.... please.

I appreciate everyones info so far, gives us some ideas to kick around. Anyone else have any thoughts?

[bwamos]

Originally posted by 400exrider707
My thoughts exactly. The guy at the shop that did the bore job told my buddy this and I laughed. Sure an ATV specific oil may have some better additives in it, but c'mon an automotive oil destroying a motor in less than 5 minutes.... please.

I appreciate everyones info so far, gives us some ideas to kick around. Anyone else have any thoughts?

Yea that guy has no clue.. lol.
Auto motive oil has TOO MUCH lubrication for ATV's because the moly's cause the wet clutch to slip. ATV/Motorcycle oils do not have those moly's. Motorcycle oils will sometimes have a higher mineral content, but mot often there's very little difference between the two other than the lack of specific moly's.

Bore may have been correct, but the rings were definatly installed incorrectly if they were lined up. You were most definatly getting blow-by.

[400exrider707]

Originally posted by bwamos
Yea that guy has no clue.. lol.
Auto motive oil has TOO MUCH lubrication for ATV's because the moly's cause the wet clutch to slip. ATV/Motorcycle oils do not have those moly's. Motorcycle oils will sometimes have a higher mineral content, but mot often there's very little difference between the two other than the lack of specific moly's.

Bore may have been correct, but the rings were definatly installed incorrectly if they were lined up. You were most definatly getting blow-by.

Well synthetic auto oil would be too lubricative, but he was running regular dino oil. It was break in time for the motor still...

Its hard to say if the rings were installed correctly or not. Originally the motor didn't smoke, so this is something that evolved as it got ridden. I know the rings will rotate a bit in the cylinder before they wear in. But for them to all get lined up... I dont know. Perhaps if the wrist pin wasn't getting enough oil, and was "sticking" the piston, and the piston skirt was riding on one side of the motor... perhaps it is possible that continuous pressure on one side forced the rings to line up like Jason Hall suggested.

[400exrider707]

Ok so Ive still been tossing around ideas with my buddy and he emailed me this morning and this is what it read:

talked to one of my friends about my wheeler and he was saying one of the reasons people have a problem with Wiseco pistons is that they are forged, and forged pistons have a tendency to expand more than a cast one would. They apparently need a pretty big tolerance and commonly make a noise similar to piston slap until they heat up, expand, and close the tolerance. I researched it and this seems to be the case from what everyone is saying. This link describes it well: http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=183. I wonder if the Foreman’s motor, being only air-cooled, runs too hot for the wiseco to handle it. My boss said that in his dirt bikes he races he has had certain machines that just wouldn’t accept wisecos, but had some that they worked fine in. He said the ones that wouldn’t were shot within a couple hours. Weird… I think I am going to order a new OEM Honda piston, pin, and clips ($70 through Service Honda) and try that.


Now the link he provided was interesting and now Im wondering exactly how a stock Honda piston is made? Any other thoughts on his decision process or any thoughts on a wiseco piston, or how about forged vs. cast?

[GPracer2500]

I believe most OEM pistons these days are hypereutectic cast rather than a standard low silicon cast. I don't know that for sure though. But stock pistons tend to be quiet, tolerant of poor warm-up practices, and call for pretty tight clearance--all features associated with hypereutectic cast pistons. I'm 99.9% sure a Foreman OEM piston would be cast (most likely hypereutectic), not forged.

A few high performance engines come stock with forged pistons (the 06+ TRX450R/ER for example has a forged piston but lower compression 04/05 has a cast OEM piston).


I've always been a believer in the virtues of forged pistons. Cast pistons aren't bad, they're just not as strong and more prone to catastrophic failure by way of cracking/shattering. The long skirts on two stroke cast pistons are particularly prone to cracking when used beyond their intended service life. Change them as often as your suppose to and they're fine (unless maybe you've got lots of HP generating mods). In a Foreman, I'd imagine the piston is stressed low enough that a cast piston is just fine--no matter how hard you rode it.

The trick with forged compared with hypereutectic cast is the correct piston-to-cylinder clearance must be used and somewhat greater care must be taken to assure the piston is brought up to temperature at the same rate as the cylinder (in other words, slowly). A hypereutectic piston is more tolerant to ripping it up right off the bat since they expand less.

I don't really here people complain about Wiseco's or other forged pistons in four strokes (either iron sleeved bores or coated aluminum bores). Two strokes seem more sensitive to setting up their cylinders correctly for forged pistons. I DO here about some folks swearing off of forged pistons in their two strokes--especially big bores like CR500R's. I never really understood why people felt that way until I had a new forged piston seize in my own CR500R. All of a sudden, I understood! I still think forged pistons are "superior". They're just more sensitive to having the cylinder correctly clearanced. The question for me with my 500 has become: is the superior strength of a forged piston worth the risk of the machinest not getting the cylinder exactly right? I'm still on the fence. Seizing a brand new piston is not fun and makes me wonder if an "inferior" cast piston is a simpler and safer choice. I think most ANY engine can successfully run a forged piston--it just needs to be clearanced appropriately for the expansion characteristics of forged.

But that train of thought really only applies to big bore two strokes. In a Foreman, 400EX, 450r, or even a CR250R or TRX250r, I'd still be likely to choose a forged piston. I haven't seen those types of engines show any unusual sensitivity to having the cylinder set up just right in order to run a forged piston. And if your running higher than stock compression, more HP than stock, etc....the extra strength of a forged piston makes more an more sense.

On the other hand, there's nothing wrong with OEM pistons, especially in a low HP application like a foreman. If your buddy had a bad experience with a forged wiseco, I think it's reasonable for him to want to try a cast piston next. I highly doubt his piston failure was directly caused by some inherent flaw in running a forged piston. But if the failure was a piston-to-cylinder clearance issue or a warm-up issue, a cast piston might have handled the situation better.

$0.02

[chad502ex]

would this be die casting and drop forging?

isn't the cast piston more porous and better and retaining oil on its surface than a blacksmith beaten forged piston?

[400exrider707]

Thanks for your input guys. I never even really knew about the differences amongst cast pistons...

[sc400ex_rider]

i would be weary of that ebay crank. people will sell junk on there