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Realistically when should I do my top end

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Posted by: ps2112---------------------

I have an 06 RMZ450 with 45 hours on it. I race +40 Junior and trail ride. When should I do the top end? I don't think I have ever hit the rev limiter, change oil every 3 hours and filter every 6. The bike still runs fine although I have noticed 2 or 3 slivers of metal, non metallic, when I cut the filter apart to examine it. I was thinking at 60 hours I would do the top end. What do you think?


Posted by: JohnRaven.exe---------------------

Meh, I'm no expert, but I think you still have a few more hours left in it.


Posted by: Octane250F---------------------

You should be able to get a lot more time than that out of a 450. A few months back Dirt Rider magazine did a long-term test of a CRF450X and I think it had something like over 200 hours on the motor and all the parts in the motor had partically no wear on them. They estimated they could have put the motor back together and easily got another 200 hours out of it.
I wouldnt worry about a few slivers of metal in the filter, for all you know they could have been from the clutch.


Posted by: ChopperDave---------------------

The 450X is an enduro motor, not so radical on the cam. The RMZ may not last quite as long?

Make sure to keep an eye on valve clearance and I would think you will know when it is time for a head job (lol).


Posted by: Rich Rohrich---------------------

At about the 12-15 hour mark your RMZ will lose something on the order of 5% of it's horsepower due to ring wear and blowby. At around the 20-25 hour mark it's pretty common for oil consumption to increase due to piston and ring wear. Whether or not these are big concerns is a fairly individual decision.

It's worth noting that the pistons in these engines (as well as the CRFs) have only a single compression ring, and almost no skirt to help support the piston as it rocks in the bore. Metal fatigue irregardless of measureable wear is a very real concern due to the design of the piston. Ignoring the recommended service intervals and playing fast and loose with the parts change schedule is what gets most people in trouble with modern four-strokes. It's pretty rare to see a failure on these engines when the service intervals are followed. The same can't be said for riders who "guess" that it will be OK when they double or triple the time frames.


Posted by: Octane250F---------------------

^so basically what you are saying is to follow the service intervals that are provided in the service manual.


Posted by: Rich Rohrich---------------------

Quote:
Originally Posted by Octane250F
^so basically what you are saying is to follow the service intervals that are provided in the service manual.


There is enough real world evidence to support using the OEM intervals if reliability is a priority.


Posted by: ps2112---------------------

So far it loses 50cc of oil between changes. I guess my only thing is that the OEM recommendations seem to be out of bed on some things and real tight on others. For example, I should change the piston every 12 hours and change the filter every 12 also. Maybe I'll do it now to get a baseline of wear.


Posted by: Rich Rohrich---------------------

Quote:
Originally Posted by ps2112
Maybe I'll do it now to get a baseline of wear.


A very wise way to proceed. Hard facts IN HAND based on your specific type of riding will speak volumes.


Posted by: Octane250F---------------------

Make sure you report back with what you find, ps2112. Id be very interested to hear what you find.
At 40 hours and considering that it doesnt sound like you run your bike hard all the time (you said yourself you dont think you have ever hit the rev limiter), I personally dont think you are due for a new topend, but its better to be safe than sorry.
Id heard some horror stories of people who were under the impression that 4-strokes run forever and never worried about their topend. Eventually they had a major failure and thats when things get REALLY expensive.


Posted by: Red Ryder---------------------

I know this is a dirt bike site but how long would you say a 200M three wheeler go before doing a top end? It's a normal four stroke engine.

Thanks
Jordan


Posted by: elcamino12sec---------------------

With proper maint the 200m should not need a rebuild unless its been beat on for years and years.


Posted by: cthowards---------------------

I have a 2005 CRF450R and did a top end at 80 hours, as well as the valves and springs. Once I got it apart, it became apparent that it did not need to be done yet. It ran fine, the valves were in spec, etc., but I just did not want to risk having it go on me so I did the rebuild. In any event, I now have a benchmark for future rebuilds based on my riding style. I ride motocross (35+ C class) and usually ride a gear high so that I am not winding it out all the time. You can check out some pictures in my members gallery.



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