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Valve and top end replacement intervals?

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How often are the valves replaced in these bikes?

I bought the bike in April, the valves had been adjusted at some point but were just below spec on the intakes and at the low end of spec for the exhaust. I shimmed them all to the upper limit of spec... .007"/.011"; right intake lobe had some scoring presumably from running zero clearance.

I just checked valve lash after about 15 hours of ride time (grown-up riding) and intakes are at .004" and .010" on the exhausts. Seem pretty quick to go out of spec?

I have a new cam and bucket ordered and will be refreshing the top end. Wondering if I should replace valves or just lap them? How many adjustments are you getting before R&R valves and seats? How often are you replacing cam chains? Any extended service interval with aftermarket forged vs. OEM pistons?

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Based on your quick experience replace the valves since you will have the head off. Aftermarket seems to last longer vs. stock however if you ride on the limiter then all valves won't last long. Valve seats tend to crack so check them when servicing. Add high performance springs to prevent valve float is a plus and lets you use more lift cams later. Up the compression is a good thing and at top end time is not much if any difference in cost. Depending on what the bike is used for you will pick different components. Pistons will last much longer than the valves so service worries are not an issue. Cam chain at 100 hrs??? maybe??

Edited by weantright

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I read somewhere in a dark corner if the interweb that you can shim them down to where you are running 1.45mm shims, which accounts for about .35mm/.014" valve train recession from new (OEM)... Then it's time to replace valves. Anyone confirm/refute? Sounds like reasonable logic.

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I know from my crf250r that once you go down two shim sizes, the valves start to pickup speed in how much they move. Eventually it gets down too a couple hours before it is hard to start, and they need to be reshimmed.

The FCR carb will always let in junk from the carb hoses. Doesn't matter how clean you keep the filter. In a dry and dusty environment, you'll realize that more quickly. Basically, valves are the cost of doing business. I know the beryllium seats last much longer. You also need the seats to be cut on a real machine, won't last just lapping them in!

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Thinking I'm gonna let it ride and see what happens. Building the head right for longevity involves a complete overhaul of the entire head at big $$... So in that context, dropping a valve isn't much of a financial risk. Will continue to monitor closely.

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Thinking I'm gonna let it ride and see what happens. Building the head right for longevity involves a complete overhaul of the entire head at big $$... So in that context, dropping a valve isn't much of a financial risk. Will continue to monitor closely.

As long as the dropped valve doesn't damage the head, piston, cylinder or cam. At $500 for KW head rebuild is much easier to swallow than $1500 complete top end +down time in race/riding season.

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I know from my crf250r that once you go down two shim sizes, the valves start to pickup speed in how much they move. Eventually it gets down too a couple hours before it is hard to start, and they need to be reshimmed.

The FCR carb will always let in junk from the carb hoses. Doesn't matter how clean you keep the filter. In a dry and dusty environment, you'll realize that more quickly. Basically, valves are the cost of doing business. I know the beryllium seats last much longer. You also need the seats to be cut on a real machine, won't last just lapping them in!

+1

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As long as the dropped valve doesn't damage the head, piston, cylinder or cam. At $500 for KW head rebuild is much easier to swallow than $1500 complete top end +down time in race/riding season.

Who does a full KW head rebuild for $500?

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Yes they are and will be inspected and replaced at the time of rebuild. Maybe additional $50-75??

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