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installed an engine with a kickstart I bought off ebay years back and it seems to have low or no compression. what am I looking at in terms of what's wrong and what needs to be done. the engine has sat unused for at least five years indoors

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installed an engine with a kickstart I bought off ebay years back and it seems to have low or no compression. what am I looking at in terms of what's wrong and what needs to be done. the engine has sat unused for at least five years indoors

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I think you have a valve that's stuck open.

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yup, i would check that the valves are moving first. pull the valve covers is the easiest place to start
 

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so if the valves arent moving how would I proceed? is there some way to unstuck them or do I need to start eeplacing things? this is new territory for me.

I should note this is à pre 2000 engine and I have a parts engine from a 2007 bike that I can use as à donor
yup, i would check that the valves are moving first. pull the valve covers is the easiest place to start
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The usual cause of a stuck valve (in your case) is corrosion of the valve stem. A simple spray of penetrating oil may well cure this, from the top. If you can get the valve to release like this, follow up with something a bit heavier, like 3 in 1 — do not attempt to start the engine, just keep applying oil until you can crank it by hand (or foot) to prove that the valve action is free

All you’re trying to do is dislodge the rust on the stem. At this point, assuming some success, you can go on to starting the engine — the moment it fires up, shut it down — more oil onto the stem — rinse and repeat

The downside to trying this without taking it apart, is that once you have the stem moving, it might let too much oil past. We call this “overhead sump syndrome” — but you might get lucky. A simple compression test will reveal all you need to know

As long as you don’t run the engine for longer than a few seconds, it can’t hurt to find out …..
 

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so if the valves arent moving how would I proceed? is there some way to unstuck them or do I need to start eeplacing things? this is new territory for me.

I should note this is à pre 2000 engine and I have a parts engine from a 2007 bike that I can use as à donor

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If you have a complete 2007 head just swap it over.
 

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Discussion Starter #8
OK so bumping this up. The valves are moving fine so it seems like it might just need rings or a new piston? How many hours would you estimate to do this and do i need to remove the engine to do this?
 

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A valve still may not seat completely or even the valve seat could be bad too. A friend of mine bought a Honda XR a few yrs back with no compression. The valves moved, but nothing. We found a bent valve from someone over revving it. Replaced the valve and everything was A-ok.

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Before getting too excited, put some ATF down the spark plug hole, like two tablespoons. Crank over and let set a little. You can take off the little adjustment covers and check valves. I’d adjust whilst there. See how much compression comes up. Maybe sufficient to start. Rings can stick from sitting too much. Might fire up an clear up. Unlikely however. I find it’s easier for major work to pull the unit. But I’m old an can’t see that good plus my back won’t let bend over too much. At least put the bike up high like on a drum or low table. Highly advise download manual, directions really help.
Go man go
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Seems as good a place as any to invoke Dan and his wisdom: Motorcycle Repair Course. This is a great resource for those just beginning motorcycle repair.

For the TW, you don't have to pull the engine to deal with the cylinder and piston, though as mentioned, having it elevated can make things easier. Depending upon the condition of the bore, piston and rings, you may need a rebore, new piston and rings, or as little as rings and a hone. Just depends on wear.

If you're willing to spend some on diagnostic tools, you can piece together a compression and leak down tester to determine whether it's the piston or the valves losing your compression. This way you can diagnose without having to take things apart and inspect. If it's routine wear (or age in the case of stem seals) it will be harder to visually diagnose anyhow, and so the tools can save you some time and trouble. That said, I would not be surprised if there's obvious damage, and if you're already ready to disassemble, I suppose you can just go for it and have a look. It all just depends on previous use, whether the bike was assembled on a Wednesday, your karma, Santa Claus, etc.
 

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Put in a Wiseco high compression piston and in the immortal words of J. C. Whitney "get more power, speed, and economy!"

Or go for a cheap Chineese 70mm piston for approx. 1/4 to 1/3 the cost of the Wiseco. I know of 2 people that have used one and both report back excellent results.

https://www.aliexpress.com/item/AHL-Bore-Standard-70mm-Motorcycle-Piston-Piston-ring-Kit-For-Yamaha-TW225-TW-225-Year-2002/32674699552.html?spm=2114.search0104.8.9.1925354fUhcaty&transAbTest=ae803_4

P1080031.JPG

Or a Wiseco 4292M06750 compared to a stock Yamaha piston -- not the cheap Chineese one. (Oversize 67.5mm. 68mm is the max for 4292.)
P4290003.JPG
 
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