top end advice

[Paul Holguin]

I just got back from Ocotillo, and I siezed my top end out there. Being as I have never done this before, I was curious as to the complexity of the rebuild. I am pretty mechanically inclined, and also have access to a machine shop if the cylinder needs to be bored. Does anyone have any pointers, or advice otherwise(bore over, stroker, ect) that they would like to share? When I bought the bike I was told that it was"built" but I dont know the extent except that it had a wiseco piston and the head was ported and polished. I would really like to use this oppertunity to get more power, but I dont want to spend a lot of loot. Any input is appeciated.

99 yz125
--Paul

[michael_loomis]

my cr250 is ported out quite a bit ... and when i went too big on the bore it overheated really easy . it was fine for the first 3 or 4 sizes over. i have re sleeved it back to stock and it cools just fine again. its easy to do.

[Vtr_Racing]

I am assuming you have a 2 stroke. If you are not familiar with this engine, here is a good website that has a lot of info for you. Some of it may not apply to your bike but the basic concepts on the 2 stroke are there. I found it very interesting...
Macdizzies 2 stroke page (http://www.macdizzy.com/)

[Ryno]

In my experience, I've based it on how the cylinder looks. If the walls are trashed, then it needs to be bored/ resleeved. If it's okay, and you can't feel any discrepancies by sliding your bare finger around, I've always honed the cylinder, and the bike ran fine. Be sure you get the right size piston and ring (.020 over, .030 over, etc). Get the piston checked with a set of calipers, or take it to the shop, and they can check it there. When putting everything back together, coat the cylinder walls in WD40, it works extremely well, and the last thing you want to do is scratch up that new pretty cylinder. Another trick I have found over the years is to turn the cylinder 90" so the rings seat on the piston where they should, then turn it back so it now faces forward again. It'll slide down easy, and be much easier to seat the rings when doing this by yourself.

[1992f150]

hopefully this helps

http://www.off-road.com/dirtbike/tech/topendrebuild/

[gosouth]

Changing the top end is pretty easy. If your lucky you won't have to have it sleeved or re-plated. Sometimes it is only a little bit more money for a new one and you won't have to wait for it. Sometimes plating takes a couple of weeks. When your checking the cylinder for nicks or scuff marks make sure that what you feel is not aluminum from the piston. if it is you can remove it with murratic acid and a cotton swab. If you find out the bore is still stock or has to be put back to stk. I would go back to a stk. Yamaha piston. I've seen to many freak problems with Wiseco pistons. I would also clean the power valves while you have it apart. I'm not familiar with Yam. ones. Some have a lot of pieces and involve being timed. Use a service manual and it will make it alot easier. Keep everything clean. And lube the cylinder like mentioned in an earlier post. But I would use 2-cycle oil or motor oil rather than WD-40. Oil is not flammable and will help coat the cylinder when you first start it until it coats itself. WD-40 will be gone at first spark. Don't use too much oil or you'll foul the plug. Also if the gasket surfaces are scratched or scarred much I would use 1211 silicone from the m/c shop. Good luck the first time is tough, but the second time will be cake.

GOSOUTH

[Paul Holguin]

Thanks to all of you guys for the advice!!!
--Paul

[Paul Holguin]

Anyone else had problems with wiseco pistons? Just curious, I thought they were good quality.

[michael_loomis]

while i have heard A LOT about "seizco" i have not had ANY problems that werent my own fault . (like not cleaning the carbon out of the stuck power valves! this happened my very first attempt at rebuilding the top end)

i have noticed that most machine shops dont pay much attention to wisecos instructions regarding an exhaust bridge. wiseco says that if you have an exhaust bridge (a small partition in the middle of the exhaust port) that you need to drill a couple SMALL lubrication holes in the piston DIRECTLY behind the port. my own pistons have never had the proper hole and i notice every time , that the ring groove gets REALLY WIDE right in this location because of it. i did the top end on my buddies vintage CZ 125 race bike ...i put the holes in according to wisecos directions and it worked excellent.... even better and longer than the guy who built the race engine just a few weeks prior ..... of course "break in" is criticle also !

[Ryno]

I used them twice. Now I prefer factory, or vertex. I know a race motor is different from a normal motor. But having to go through stuff with a 2 stroke is rediculous. If we were talking about a 500hp Chevy small block, it would be a different story.

[choppekx]

Just got the new dirt rider in the mail, they have a whole article dedicated to rebuilding a top end

[partybarge_pilot]

The old sezcos were crap. They had a nasty habit of growing oval on you. I don't know if they have fixed this problem as I haven't dared to trust one in about 10 yrs.

[empire231]

I used wisco on my old rm125 and it worked fine... never had a problem with them. used a vertex piston on my friends cr and to this day he still doesn't like the way it's running after the new top end?? maybe it has a bit to do with the bike?

[Paul Holguin]

OK so I pulled the head off and I think the piston might be out of spec(see picture.) The bottom end seems to be somewhat seized as well, buit I am sure that this is due to a chunk of piston down there. On the positive side, the cylinder walls looked and felt alright, no eching/pitting. My next question is, what do I need to do in the bottom end? It looks like a real pain to remove the whole motor, as the swing arm is connected to it. What else should I check for in the bottom end? Thanks to all of you guys for your help!!

-Paul

[empire231]

WOW! your cylinder is still ok after that? well if you think your bottom end is gone then you should take it to a shop. they're most likely gonna have to split the cases, and that can be very difficult. you might have thrown a rod, and it just needs to be rebuilt...

[JeffS]

That pic is called 'detonation'. The bike leaned way out and that destroyed the piston. There may not be a missing chunk, usually that hole is caused by melting the piston away, but if the bottom end has metal in it, then it needs to be torn down by a shop. yuck.
When my 250R had the same problem, I was able to get away with just changing the piston and rings. My cylinder wall wasn't damaged either.

[Paul Holguin]

Yeah it definatly ran lean. I thought you might get a kick out of this too, note the ground strap and electrode(or lack thereof).

There definately are some chunks though, I was able to pull out some large pieces. The rod does not seem to be bent, and the crank seems to move freely until it hits a certain point, which is why I believe there is a chunk of metal stuck in it.

Also, what lubricates the bottom end? Is it the gear oil for the tranny?? I dont think so, but with my knowledge of car/truck motors, it seens inconcievable that nothing lubricates the rod, crank, and crank bearings.

A little moto tech 101.

[Paul Holguin]

Next question, who is cheap and good for bottom ends, and what should I expect to pay? By me, there is only Mission Yamaha, and they have a tendancy to bend people over, no lube. I do not mind taking the bike somewhere else in the area(OC, 909, ect.) to get the work done.

[empire231]

when my 125 went out, I took it malcolm smith and I think I payed $475 for the bottom end rebuild (rod&bearings). that was almost 5 years ago

[stuckthrottle]

the bottom end (pin and connecting rod bearings) is also lubed by the premix oil.

[Ryno]

2 strokes share the crankcase/ transmission oil. That is SEVERE detonation. That plug should be a nice brown color. White is a severe lean condition. I would drain the oil, and see what comes out before you go ripping into a bottom end. Try to refill it and flush it out even. I would go to Precision Concepts in Temecula. They do my suspension, and will advise on a good shop. That's a super bummer man.

[michael_loomis]

my CR has the tranny gear oil seperate from the crankcase http://www.race-dezert.com/vb3/attachments/old/images/graemlins/smile.gif

the crankcase is lubed by the premix but the crank has seals on the ends to keep the gearcase seperated or else it wont suck in any air. (sorta like a vacuum leak)

ive been too intimidated to tackle any bottom end issues ... and shops are pretty pricey when it comes to splitting the cases.

[Paul Holguin]

Anyone want to buy a bike?

Just kidding. Thanks again for the words of wisdom guys, I guess this thread sould be called bottom end advice now http://www.race-dezert.com/vb3/attachments/old/images/graemlins/ooo.gif

Ryno, are you saying that I should see if I can just " flush" out the bottom end? Thats kind of what I was thinking, but I am uncertain how severe the damage is down there. I was able to dislodge several large chunks, and it freed it up a bit, but there is still that one spot that wont move.

For what its worth, should I try to see if I can make this bottom end work, and put it back together? This route would only cost about $100. I can see the cycle trader ad now...............fresh top end, runs great............................. http://www.race-dezert.com/vb3/attachments/old/images/graemlins/grin.gif

I guess there is little to lose ($100) if I try that out right?

[Ryno]

Mike-

Your right, I don't know what the hell I was thinking. Maybe a CRF?? a dozen or so beers will do that I guess.

[michael_loomis]

Ryno .... no problem bro .... i know what you meant ! lol

ya i cant remember which of the new 4 strokes shares and which are separated.

lol bottom end advice ! jog regularly , do squats , leg presses .... oh wait .....

that one tight spot is bad news ....

[Project1500]

Talk to three bros in costa mesa. Also what premix/gas ratio were you running again?

[Paul Holguin]

Thread Revival!!!

I had to bring this one back, as I got the bike back and took it to Ocotillo again.

It ended up needing new bearings in the bottom end, and obviously everything else from there on up. After calling around, I ended up taking it to Mission Yamaha, and they were surprisingly gentle. It cost just under a "G" for everything. Per the techs advice, I am now running 32:1and VP fuel as opposed to the 50:1 mixture the manual recomends. This one should last a bit longer......

I just wanted to bring closure to this as I am sure you all lost sleep over it.... http://www.race-dezert.com/vb3/attachments/old/images/graemlins/smirk.gif