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1990/1991 Cylinder Swap & KIPS Timing. w/ pics.

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I recently recieved a 1991 KX 125 from a good friend with little mechanical knowledge and disposable income. This summer it gradually lost compression until it wouldn't start. Later I told my friend I would take a look in the motor for him. He sheered part of the ring and it put a vertical gauge through the cylinder and the piston was shot. I'm financially well off so I agreed to pay for all the parts up front with the idea that I will be paid back or he will work for the money owed.

So I bought a 1990 KX 125 cylinder on ebay that is in good shape. I was thinking the cylinder was exactly the same as 91' but now that it's my hands there is one difference I'm worried about. Eric Gorr points out that the 91 has an additional roller pin on the opposite side as the exhaust. I was planning to use the 1991 head but with that extra roller pin, the 1991 head will sit flush on the 1990 cylinder. Do you think I could save some of his/my money by pulling out or cutting that extra pin? Or should I just buy a 1990 head for another $50?

Secondly, I don't have a manual for this bike and finding information on the net regarding the KIPS timing is proving to be difficult. Right now I'm at an educated guess as to how these line up and I believe it's correct, but let me know if I am wrong.

The first thing I did was put in both valves halfway and then slid the rod all the way through to the end. Then I dropped the valve down and lined up the left valve's dot onto what I believe is a hashmark on the governor rod. You can make it out on this pic if you have good eyes. (obviously the rod is outside the cylinder, I took the photo so you can see how I lined it up once it is installed within the cylinder)

2012-02-16120336.jpg

Next, I secured the rod in the cylinder by tightening the philips head at the end of the rod. Then I pulled the rod all the way out as far is it went. Later I lined up the dot on the right valve with the hash mark on the idle gear spur. If you have good eyes you can make out the dots on the valve as well as the gear.

2012-02-16121442.jpg

After looking through the exhaust port and checking to see if it works, I notice at no time is the rounded part of either valve visible. When the rod is pushed into the cylinder, a smaller port is opened. When I pull the rod out, a larger port is exposed through the valve. I'm not sure how else to describe this.

Thanks for taking the time to read and answer or confirm my questions. My friend and I really appreciate it. Thanks.

Edited by pCp 450

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I don't use the marks, I just put them together and make sure they are closed when pushed in and open when pulled out. In the passed I have found the marks to be off. Anyway when closed (rod pushed in) both side valves are blocking the port to the cylinder and you see the flat part of the side valves when you look in the exhaust port and the. When open (rod pulled out) the side valves rotate so the flat part is to the outside opening the port to the cylinder and when you look into the exhaust port you can see the whole side port is open. I hope that helps.

Ed

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Yes that helps. In my case, when the rod is pushed in it blocks the outside port but there is still a small port open. When pulled out the larger port is exposed. Man it's tough putting this in words when it's so simple to look at.

The rounded part of the valve should not be visible at any time, correct?

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Yes you don't really see the rounded part of the valve, and yes it is very hard to explain. When the rod is pushed in there should be no part of the port open. And also yes pull out the extra pin in the head.

Ed

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on my kx250 (2002), the marks did not line up either. i had to do it like Ed said, by sight. pay attention to what the valves do when you look in through the exhaust port, not the side resonator chambers. when looking in the exhaust, with the rod pushed all the way in, the valves should shut off the side ports. when the rod is pulled all the way out, the valves should be all the way open.

check out my thread for some visuals:http://www.thumpertalk.com/topic/940930-02-kx250-kips-powervalve-timing/page__p__9841550__hl__02%20kx250__fromsearch__1#entry9841550

its not the same powervalve, but the way it works is very similar. the difference is that mine has 3 stages, rod in, rod out, and spring all the way back, yours is 2 stages, just rod in and rod out.

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