Compression low?

[Wellsy]

I have a couple of issues that I need to find answers to. First off, I have a 2005 ec250, according to the shop I took it to, they said the compression measured 110 and that was low. I was wondering what it should be.
Second, if the compression is low I would need rings. Should I replace other parts while I’m in there? I’ve been shopping on ebay and gofasters and found two kits. One is a complete vertex kit that includes pistons etc. Described below from ebay:
COMPLETE TOP END OVERHAUL KIT FOR GASGAS EC,XC,DE,SM 250 .INCLUDES VERTEX "A" PISTON WITH RINGS ,PIN & CIRCLIPS .HEAD O-RINGS ,BASE GASKET ,BOTH POWER VALVE GASKETS ,WATER OUTLET GASKET AND WRIST PIN BEARING
The other one is from the Gofasters and it is a Wiseco.

The last question I have is – If I’m doing the rings, do I need to have the cylinder honed or sleeved or what? Obviously – I haven’t done this before but it will be my winter project. Thanks in advance.

[barkeater]

We lost compression on an 01 XC250, when we pulled the top end, the piston looked like it just came out of the box. We snapped in new rings, new pins, honed the cylinder, cleaned everything up and buttoned it back up. Just like new. It's been raced hard in D23 by 3 owners on the original Wiseco piston.

I'd go with GoFasters for the parts. But unless your piston is in poor condition, I'd keep it.

[JoshP]

You need to take it apart and do a good once over to really determine what you need. Inspect your piston and cylinder to make sure you do not have any abnormal wear to either. BUY THE REPAIR MANUAL!!!!! especially if you have never done this before! I just got finsihed read a nightmare on the Woodsracer board about a CR 250 rebuild where the piston was installed backwards and the answer given was that he could not afford the manual. Well if you can't afford the manual you can't afford to buy or service the bike. This is not a hard thing to do but can have a bad affect to your bank account if you do it wrong and mess things up. You most likely will not need to service your cylinder since it's an 05 unless it has been beaten senseless.
Good Luck with it!

[Wellsy]

It hasn't been beaten senseless, just trail ridden. Where can I find this manual? Is it different than the one that came with the bike?

[barkeater]

I think this is the workshop manual JoshP is talking about. It's a pdf, so you just need to find a good printer that will kick out 71 pages.

http://www.gasgasmotos.es/rcs/manual...r_ec06_eng.zip

[Wellsy]

Thanks a lot, that should work! I'm sure I'll be posting again once I'm deep into it.

[JoshP]

Nice one there Barkeater. I totally forgot they put that into a pdf.
Just take your time while doing the top end and you will be fine.

[GMP]

With both .5mm and .3mm base gaskets, stock head, my '07 250 measures 185 PSI. With a single .3mm gasket my '03 was 195 PSI. This is at approx. 1000', 70 deg F.

How many hours on your bike? There is more to piston life than wear. The skirts fatigue and can crack if run for too many hours. I do a top end every year and rest easy I can ride the bike hard without worry the entire next season. The Vertex is a good piston, now OEM on '07 bikes. You need to find the size of your cylinder ("A" to "D", stamped on rear), and get the corresponding size piston or one size larger if you have a solid season on the cylinder. This has worked well for me for years now on three bikes. Of course this assumes that the Nikasil plating is in good shape.

[barkeater]

Originally Posted by JoshP

Nice one there Barkeater. I totally forgot they put that into a pdf.
Just take your time while doing the top end and you will be fine.

What I lack in mechanical know-how, I make up for with mad google skillz.

[Wellsy]

GMP,
I ride in higher elevations – from about 6000 ft to around 12000 I would guess. The temperature can vary anywhere from 85 down to 25 or so. I don’t ride if it’s colder than that. The stamp on the back of my cylinder is an “A”. I don’t know how many hours are on my bike – I’m the second owner but the computer shows 1800 miles on it. What piston would you recommend?
Thanks for all of you guys helping me out – this is a fantastic site!

Barkeater – they say the smartest man doesn’t have all of the answers; he just knows where to look!