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Valves and preventive maintence

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I found this in the "technical" section on thumpertalk.. Its a good read.. They talk about the crf but I think it is good to read.. Also there are a list of recommendations and this is what we should read.. Some of you may already know all this but for those that dont read on :) I purchased the 110 vp leaded and mix it 60/40 with pump 92 octane from 76. Ive talked to VP rep, varner..and a couple other engine gooroos and they recommend it..

The Valve and what it does:

The 4-stroke valve is no more than a door. This door opens and closes a port inside the cylinder head at a very high rate depending on the engines RPM. The device that opens and closes the valves is called the camshaft. Between the cam and the top of the valve stem is a specified clearance called valve lash or valve clearance. There are two different valves, the intake valve and the exhaust valve on a 4-stroke engine.

The intake valve opens at a precise time and allows fresh mixture of air and fuel into the combustion chamber (area above the piston inside the cylinder). This valve is normally bigger than the exhaust valve.

The exhaust valve then opens after complete combustion has taken place at a very precise time and allows the burned and unburned mixture to escape by the piston pushing out the gases then closes and ready for another fresh charge of air and fuel to be enter from the intake valve.

What is the problem with CRF valves:

The most common problem with CRF valves is that the valve face wears into the valve seat on the head called mushrooming. When this occurs the valve will get closer and closer to the cam, valve clearance, when the valve gets to close to the cam it will hold open very slightly not closing all the way when needed and will cause compression to escape in which will be low compression and hard to start or not start at all.

NOTE: These valves are made from Titanium

Why are the CRF the only ones having these issues in a short period of time:

Well first of all it is not all the valves it is only the intake valves having this dramatic wear. The exhaust valves are not mushrooming. There are many reasons and probable causes for the intake valves mushrooming.

1: Eating dirt or dust coming through the air filter, bad seal on the air filter or air boot.

2: The profile of the cams intake lobes, very tall with a short duration, is causing the valves to slam shut.

3: Some aftermarket valve companies are claiming that Honda has poor grade of titanium.

4: Very high heat from unleaded race gas such as Ultimate 4, or lean carburation.

Recommendations

1: Use a leaded race gas such as VP 110, you can mix it with Ultimate 4 or 92 pump, the lead in the fuel will help cushion the valve face against the seat.

2: Make sure your air filter is sealed well, as well as the air boot to the air box.

3: Have you valves adjusted after the first 10 hrs. And every 15 hrs afterward.

4: Adjusting the intake valve clearance on the tight side of the specified clearance to keep the cam lobes from using the hammer effect on the valves.

5: If you are beyond the preventive point and the valves are already mushroomed replace them with either new OEM valves or using the Kibble White valve kit depending on your budget.

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Been running AVGAS 100LL since day 1 in my RMZ.Siliconed cage to airboot. Good tips

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Good read. I guess I will have to check my valves on my new RMZ-450 because I am getting close to 10 hours. Anyone have check there valves on their RMZ and noticed that they already need adjusted after 10 hours?

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Good read. I guess I will have to check my valves on my new RMZ-450 because I am getting close to 10 hours. Anyone have check there valves on their RMZ and noticed that they already need adjusted after 10 hours?

Checked my valves at 3 hrs, then 4 more times.Total hrs about 40 plus. Valves are holding.Exactly same clearance now, as it was at 3 hrs.

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Good read. I guess I will have to check my valves on my new RMZ-450 because I am getting close to 10 hours. Anyone have check there valves on their RMZ and noticed that they already need adjusted after 10 hours?

I check my valves and chain once a week. I havent had to adjust the valves yet. But the chain a couple times. I've got about 30 hours on mine.

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Haven't had to shim a RMZ450 yet. We have many more hours on some RMZ450's without shimming. RMZ450 is the best !

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