Jump to content
Sign in to follow this  

How do I know if I need a new top end?

Recommended Posts

I just bought an 02 crf 450R off of a guy and its very well maintained and clean. He was the original owner and he only rode it maybe once a week for a couple of hours in the summers. And we only trail ride.. nothing too hard. The only time he put a new top end in it was a year or two ago.(so the first one lasted him probably almost 4 yrs.) So my question is, how do I know when it needs replaced??? Im used to riding 2 strokes, and I just have no idea about these 4's. When its warmed up, it will start the 1st or 2nd kick. But it could take 10 or so kicks when its cold outside.(Like 20 or 30 F) I would LOVE to get some advice!! Thanks!

Share this post


Link to post
Share on other sites

Seeing as you live in the Northeast perhaps you should take it apart and inspect it in the off season. It's a few years old. Might be time for a new accelerator pump diapragm and a valve check is a must. It would be interesting to see how the top end looks. While it's cold out take some time to go through it.

Share this post


Link to post
Share on other sites

Modern 4 stroke motocross bike the pistons wear out faster than the rings so leak down test will limit the ability to gauge the condition of a competition engineered motor like this.

Just take it apart, and put in a new piston and rings. If you are asking yourself if its due, your probably far past needing it.

Share this post


Link to post
Share on other sites

Well, I just bought the bike and I dont have an UNLIMITED budget, so I can't just "put new rings and piston in." How do you check the valves and do a leak-down test?

Share this post


Link to post
Share on other sites
Well, I just bought the bike and I dont have an UNLIMITED budget, so I can't just "put new rings and piston in." How do you check the valves and do a leak-down test?

Get one of these (center/top):

http://shop.thumpertalk.com/catalogs/Tucker_Rocky_Offroad_2006/default.asp?p=929

They're ~ $160.00, but you'll spend at least that at a shop for the same service - just a fig'n test, forget the cost of any other labor/materials. Buy the purpose-built tool and you'll be able to do them for you and buddies and never spend another dime @ a shop.

Share this post


Link to post
Share on other sites

another thing to think about is new crank bearings.....if one happens to go out.....BIG MESS!!!!

Share this post


Link to post
Share on other sites
Well, I just bought the bike and I dont have an UNLIMITED budget, so I can't just "put new rings and piston in." How do you check the valves and do a leak-down test?

You're obviously a candidate for wrenching on your own bike. Take a tip... buy the tools and do the work yourself. If your budget is limited, you need/want to do the work yourself. The goofs @ most shops will charge you for just looking at your bike to determine if they want to work on it today or next week!

A leak-down test is done buy removing your spark plug, threading in a hose that you then connect to compressed air. You run in ~ 70 psi and watch the guage. As a general rule, anyting below 5% is good. Any reading greater than 5% may require further investigation. It's a dead simple tool and now that I own one, I could duplicate it with parts from home depot for a fraction of what I paid MP for it, but I have a policy of not looking back, so I'm good w/ what I have.

Share this post


Link to post
Share on other sites

179$ for a leakdown tester seems really high. I bought one off of a snap-on truck for 120$. It is not a snap-on tester though, it is a thexton tester. and it has two guages insead of the one that is in the picture. If you look aroung you could prob find one for like 100$

Share this post


Link to post
Share on other sites
How often do you guys usually preform the leak down test on your bike? Do you do it on a regular basis or just when you feel it's time for a new top end?

Leak-down testing is real easy. Anytime the tank is off is a perfect opp.

Share this post


Link to post
Share on other sites

Single guage leak down testers....eh......I think Snap-On makes the best one money can buy and i am by no means a brand slut when it comes to tools. I use what works best versus how often i use it and the quality and usability.

May not be the best choice for working on just your own bike, i do this for a living so its a bit different of a situation :applause:

Share this post


Link to post
Share on other sites

Well, this evening I decided to tear into my bike and I checked the valve lask and decomp arm. I was please to find out that they were all within spec! Thats a good sign, right?!?! The spark plug was black, so Ill have to get a new one of those tomorrow.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×