Top end rebuilt?

[Z71_Willy]

Hey guys,

I'm trying to tell if I need a top end rebuild for my xr400. It seems to be burning off oil. I believe something like 3/4 a quart of oil to 500-700 miles. An the compression is to a point where I can turn the motor over with my hand but not start it with my hand. I don't even need the conpression release to start the bike.

Thanks

[GU520]

You have automatic compression release in your XR400, so turning the motor over with your hand is quite normal.

 

Burning this much oil is not.  Are you sure you are measuring the oil level correctly?  It is kind of tricky on the XR4… Do a search..

[Oil Baron]

What oil?

 

Does it smoke?

 

What oiI change interval?

 

How old is the oil in the bike now?

[trooper8]

If it turns over easily by hand in my experience it's probably due. What does sparkplug look like; verify the oil consumption; loosen valves and do a compression test.

[Wallander]

Sorry to hijack your thread,  trail_runner, but while talking about valves and easy turning...

 

 

My 11.0:1 high-compression 426 does not have auto decomp, and I can't turn the engine over with my leg without using the manual decomp. But, starting it today, it run fine for 2-3 mins, warming up idling, then it shut off on its own, which is strange. I looked for TDC to fire it up again, but now without touching the manual decomp lever, I could turn over the engine easily! The manual decomp cable, lever, etc. were all fine and working, but there was no real compression.

 

I kicked it a few times (I could not find TDC), then it started and run fine all day like a champ, with numerous intentional restarts.

 

What happened? One of the valves could not close? Air filter is clean (was cleaned 2 rides ago) and seals fine.

 

Thanks.

[GU520]

Ok, in case the OP is a new XR4 owner and getting increasingly confused, let’s explain a few things.

 

The XR4 has both a manual decompression system (lever on handlebar) and also an automatic decompression mechanism that is located on the camshaft.

 

So a healthy, stock  XR4 can easily be turned over by hand (even a brand new bike) the resistance of the kick start lever tells you absolutely nothing about the  engine compression.  If the engine is not stock (for example has an aftermarket camshaft)  there can be no automatic compression release, and you will feel the full compression of the engine when you push the kick start lever.  In that case you can not turn over the engine by hand unless there is a compression problem.

 

Regarding the oil, it is very common for new XR4 owners to get false readings when they measure the oil level, it is kind of tricky to do correctly.

 

So please,  before you rip the engine apart, confirm that you have a problem in the first place.

[Z71_Willy]

Baja rambler

The bike is an 2001, I change the oil every 1000 miles, last time I rode it had a little smoke from the exhaust after riding for about an hour hit that was when I turned it off.

[Oil Baron]

Baja rambler

The bike is an 2001, I change the oil every 1000 miles, last time I rode it had a little smoke from the exhaust after riding for about an hour hit that was when I turned it off.

 

Change the oil and see if things improve.   20W50 is the recommended oil above freezing temps.  

[Z71_Willy]

Ok I'll do that. Xr4s take just about 2 quarts correct?