the story
hey I had a heck of a friday (my off day from work) I installed the 12 tooth front sprocket on my bike after about an hour the quad started running rough I shut it off and the motor seemed seized. I hike back to my truck and trailor and start heading to get my quad theres a mud hole I have gone through before at the entrance to this riding area so I start powering through, and find a large hole. water went up to the lights and I was on my way out the other side, motor stops. I hydo locked the motor in my truck fortunatly no rods are bent. I had to call some friends with 35-40 inch mudders to go and get my four wheeler and pull my truck out, got it towed home and now I have it running.

the quad
So I began pulling my motor apart last night on the 400 I have it all the way removed jug and up. the underside of the stock piston skirting had cracked off. there were some metal pieces in the exhaust headpipe and in the crank case there were a couple large pieces down in the crank[img]i/expressions/face-icon-small-shocked.gif[/img] I was able to turn the flywheel and pick most of them out when the crank brough them to the top.

The weird thing or maybe a plus is that the stock jug has no signs of scoring at all. I have no idea how but the stock pistons sits correctly and I have cleaned and rubbed my hands all over the inside and there is no scratches or anything. Can I just drop a stock bore wisco in its place? I couldn't figure out how to remove the piston from the rod what tools are needed to do this?

How do I get the motor broken down to the crank? I want to make sure all the metal is out of there. I had it suggested to me I lay the quad upside down and turn the crank again until flushing the crank with oil to get it all out. Is there a drain plug for the crank case? I didn't see how I could get the case open.

noe the fun part I definatly will get a new piston, but while its apart what do you guys think if this?

decking the head, and having the flywheel race lightend since I have removed my starter anyway. How high of compression can I run on pump gas?

keep in mind im running the stock pipe so theres probable not much use in porting.

all info is appreciated.

 

conig, man that really sucks. glad the trucks not hurt, could have been alot more costly. as for the quad, seen a few stock pistons broke. main thing to check is the crankcase itself. the clearance between the case and crank is very close and pieces of the piston can cause a break in the case. i would go oversize with a wiseco, and trim the head. the other thing you can do while the jug is off is plug the decomp hole in the exhaust. just tap it and put in a setscrew with loctite. personally, i would pull the whole motor apart to make sure there are no pieces of debris in the bearings, etc. also, it wouldn't hurt to do a mild port, that way if you do change the pipe you'll be done. it'll also make a difference with the stocker on.

are you running a pump block off??

 

more than likely the skirt broke because of excessive clearance, you need to carefully measure the cylinder bore before you put a std. piston back in.I would NOT recommend just cleaning the aluminum out, take it apart!! ive seen aluminum get wedged in bearings and you will not get that out without disassembly. as for mods, a good cleaning of ports(remove flash) will help. as for the head I run 65 thousandths squish, but the jury is still out if it will live on 92 octane. it should in my experiance with snowmobile engines. get a spanner nut socket for the mag side nut, flywheel puller and a manual. you'll be set. good luck

 

same thing happened to me a few months back. It took out my case and the bearings were full of metal pieces. you should DEFFINATLY check yours CLOSELY before you reassemble, changing all seals, etc. while you go. Also, be sure to clean out your exaust pipe, the metal pieces get stuck in the oil, etc. thats in the pipe.

 

thanks for the replys guys.

I would have really been pissed if this had happened at orange crush this weekend. fortunatly the reality of the potential vehicle cost and the relief of not needing to rebuild a mopar motor makes it seemed to keep the whole incidents in prospective.

I may be dumb abnd am at my girl friends house now but can't seem to figure out how to get the case apart to get the crank out or how to remove the piston(wrist pin). I didn't really have the time to really look it over though. My brother worked at the local polaris dealership for 5 years,I worked there for one year, and he knew more about the mechanics of the bike he got the jug off in literly 5 minites and diagnosed the problem. To bad he doesn;t live closer.

Also my rod has surface rust on it is this normal?

Jefro yep I'm running a block off, the motor went lean for some reason as well, the plug electrode had white specks all over it. I'm really not sure why becuase the weather was the same and I didn;t touch the engine at all just changed the front sprocket. I did switch t a different oil in the last month but it checked out to be sufficient.

So I need to .
1. flush out the pipe.
2. measure cylinder wall clearance or ust get an over boar. (the stock piston fit real tight, I had good compression and everything)
3. clean out the crank and/or open it (if I can get it open)
4. get a flywheel puller remove fly wheel
5. get the head decked.
6. clean up the ports flashings .

now if I just figure out how to do all this stuff. [img]i/expressions/face-icon-small-wink.gif[/img][img]i/expressions/face-icon-small-blush.gif[/img]

 

conig, forgot all about orange crush this week. going to make ga if possible?
taking the motor apart's not real hard, but a service manual would be the best bet. you'll need to remove the recoil, flywheel, ign. sys, counterbalance gears, clutches, and what not to get to the case. the take out the bolts holding it together. using some heat to get the cases apart realy helps. just heat around the bearing area some and they'll come apart. another thing, the slotted nut behind the flwl is left hand thread.

as for the cause, the skirt breaking would lead to believe that there was a little too much clearance and caused piston slap. the stockers don't like that as you've found out. i just got done putting my motor back together for the season, too. just needed cleaned up inside and its ready to go hopefully by the weekend.

 

jeffro not looking to positive for washington ga isn;t that this weekend? fefinately don't think I could have everything ready if a complete tear down is in order by the weekend only getting acouple hours after work to do the job. is your fly wheel machined? it seems this could hurt for trail riding, etc.

an over size isn't a big deal I'll call a local engine builder tommorrow about the head and getting the jug bored out. may try rick since I will be off, I can never get ahold of him otherwise. atleast maybe for the fly wheel.

 

that would be cuttin' it pretty close by sat. wouldn't it. no my flywheel is stock. pretty much all of my bottom end is, except for no pump. they can lighten the wheel and still have electric start, which would be nice for xc dead engine starts. still would give a quicker rev and not have to pull on the start line. i may do this next. i run a pretty light primary weight set with the aaen green spring, so the quick rev hasn't been a problem, great for tight woods. on the last couple of heads we had about .020 taken off. makes good comp boost and still ran prem pump gas. another thing to do is to add a little additive in the fuel. maxima's HiTest for the last couple of yrs at 2oz per gal.