Upgrade to 300 cc?

[Francisco Zapata]

Hey guys! I've having trouble with the compression on my '09; I've already read the manual, looked for info here on the blog; and it looks like I have to either bore the cylinder, or buy a new one, which I think this last option would be cheaper, paradoxically. Looking on both amazon and E-bay I found that they have a new big bore cylinder kit; but this one instead of having just 250cc, has 300cc, advertising that as an upgrade. The link is in the end of this post.

Do you think installing that 300cc cylinder would be a good idea? Any thought on it?


Thank you in advance.


https://www.ebay.com/itm/For-SUZUKI-GN250-GZ250-DF250-LT250-DR250-BIG-BORE-Cylinder-Kit-Upgrade-to-300-cc/183897987868?_trkparms=aid%3D111001%26algo%3DREC.S EED%26ao%3D1%26asc%3D20160908105057%26meid%3D53ea1 4314c4e44d3887cff4478bed93d%26pid%3D100675%26rk%3D 1%26rkt%3D15%26mehot%3Dlo%26sd%3D183897987868%26it m%3D183897987868%26pmt%3D0%26noa%3D1%26pg%3D238005 7&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Af819f2d8-f44d-11e9-99ec-74dbd180bdbb%7Cparentrq%3Af0547e9d16d0a9cc84d3418e ffe45bf9%7Ciid%3A1

[wacio]

We had user here that would be able to comment on the quality of Chinese replacement parts. I remember him doing cylinder piston replacement. Before you jump on this I would recommend to do full diagnostics. Bad compression could be caused by many things:
- bad head gasket
- incorrect valve lash adjustment
- burned valve
- loose spark plug
- worn piston rings
- worn piston (rind grooves)
- worn cylinder
- crack in the head or cylinder
also less common:
- broken starter clutch - just starter spinning
- broken or leaking compression tester

So check few things before firing parts cannon.

My $.02 on the 300cc mod: Would not do it. Even if you'll end up with well running bike, with acceptable level of vibrations - you'll be putting additional stain on the crank, clutch and trans.

[Francisco Zapata]

Thanks for your answer and your suggestions, Wacio.
I checked both the head gasket to see if there was any air escaping between the cylinder cover and the cylinder head: nothing. I checked on my valves and they're in good shape. I tight the input of my compression tester as I should've (according to it's owners manual) when I tested the compression; both my cylinder and cylinder head has no cracks. The only thing I can think about is either a worn piston and cylinder; because I changed my piston rings for a brand new ones about a month ago, and I still had the compression issue.
About the broken starter clutch, I had no idea that it'd be a possible cause of low compression. Do you have any idea about how to check if I have something to resolve there?
I think you're right on the possible consequences on upgrading the cylinder to a 300cc one. So, I think I'm not gonna do it; But i already ordered a big bore kit of 250cc. So, I hope that installing it and checking my valves clearances would be enough to resolve my compression thing :)

[wacio]

Francisco - I'm listing it as unusual because broken starter clutch may cause engine to rotate slower, or not rotating at all. You'd hear starter run but engine would be still or rotating slower than intended during test. Than of course you'd have low/no compression. You could connect external tachometer or multi meter counting 12V signal to ignition coil (most multi meters can display frequency).