Top End Help?

[rickyk22]

I have a 01' KX-125 and I just rebuilt the top end this weekend. I bought a weisco piston for my bike. however, after I got done I noticed that there are two small holes on the back side of the old piston (exhaust holes?) and there werent any on the new weisco piston that I put in. I was just wondering what the holes were for and if I have to take the new piston out and drill them or if it is fine without the small holes.

Thanks alot,
Rick

 

[nickyd]

lubrication holes for the exhaust bridge - check the pink paper instructions that came with the piston

 

[rickyk22]

what would be the consequences of not having lubrication holes for the exhaust bridge?

 

[nickyd]

i have seen holes burned in the pistons at the bridge. if they were there on the piston you took out, you should drill them in the new one

 

[dante]

I did'nt drill holes in mine and it is fine so far... It's been over 5 months, and it still runs fine... And I pretty much flog the thing constantly whenever I ride...

 

[SpeedyManiac]

I wouldn't drill holes in it. Wiseco didn't put holes in the piston for a reason.

 

[nickyd]

I wouldn't drill holes in it. Wiseco didn't put holes in the piston for a reason.

why do their instructions say to do it then?

and for the record, i'm not being a dik.....i called wiseco about this - 800-321-1364, option 1, if you think i'm wrong....I personally learned this lesson the hard way once and would hate to see someone else learn it too.

anyway, IF you have an exhaust bridge in the cylinder, its recommended that you drill lubrication holes in the piston. As noted above, Wiseco didn't drill them b/c that piston fits more than one year's bike/model and one of cylinders it fits does NOT have a bridge.

 

[SpeedyManiac]

Sorry, I didn't realize the instructions say holes must be drilled in the piston. If the instructions that came with the piston say the holes must be drilled, then definitely do it. I misunderstood the previous replies as there was no holes in the wiseco piston and they're instructions did not say to drill any. Sorry.

 

[Fultoncm]

I just put a wiseco piston in my bike and it also came with instructions about drilling holes. It's legit.

 

[Rcannon]

Put the holes in. Many of the bikes will form a nice groove on the exhaust bridge if holes are not there.

Weisco says they dont put them in because the exact location of each exhaust bridge is different. Makes sence, I suppose.

 

[rickyk22]

Thanks. i am going to pull it out and drill the holes this weekend. I will be an expert at taking my top end apart by the time I am done.

Also, how should I break the new piston in?

 

[nickyd]

cool - you good with the way to do it? if not let us know.

 

[rickyk22]

I know how to change the piston, it wasnt too hard. I just have two questions. since I rebuilt the top end and only rode my bike for a 1/2 hour, When I take out the piston to drill the exhaust bridge holes, I won't have to change the seals again, will I?

Also, how do I break the new piston in? I am assuming that I should take it easy and put a few hours on it before I really open it up, but I was wondering if there is a formal way to break it in.

thanks for all the help.
Rick

 

[Joshtee]

just to get this right. I just put a new piston in my 2000 kx125/144 and the instructions did not say to drill any holes in it. Would that mean that that particular piston should not be drilled?

Also, about break-in. I got this off of Eric Gorr's web site:

11. When you initially start the engine after a rebuild, manipulate the choke to keep the engine rpm relatively low. Once the engine is warm enough to take it off choke, drive the vehicle around on flat hard ground. Keep it under 2/3 throttle for the first 30 minutes. Two common myths for proper engine break-in are:

myths
1. Set the engine at a fast idle, stationary on a stand.
2. Add extra pre-mix oil to the fuel. When the engine is on a stand it doesn't have any air passing through the radiator and it is in danger of running too hot. When you add extra oil to the fuel you are effectively leaning the carb jetting. This can make the engine run hotter and seize.

 

[nickyd]

just to get this right. I just put a new piston in my 2000 kx125/144 and the instructions did not say to drill any holes in it. Would that mean that that particular piston should not be drilled?


depends - is there an exhaust bridge on that bike?

 

[89yz250]

Signs and Symptoms of a Top end!!!!\

What are the signs and symptoms of a weak top end?

 

[nickyd]

What are the signs and symptoms of a weak top end?

a bunch....to name a few....

low compression, hard starting, loss of power, rattles, dead spots in the accerlation, etc...there are exceptions to all of this - i've seen bikes with low compression fire right up....bikes that rattle and clank have a ton of power....

 

[rickyk22]

I will probably sound like a complete retard asking this question, but:

What exactly is an exhaust bridge, what does it look like and where is it?

I think it bridges the exhaust ports, but what exactly does this do?

Thanks,
Rick

 

[nickyd]

you've got it - look into the exhaust port - you'll see a thin metal bridge in the middle. it keeps the ring(s) from popping into the port.