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MitchAustralia

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Haha, well put and yeh I know what you mean.
Dad is very good with everything when it comes to teaching me and letting me watch in.
Just this one thing he seems to believe that valve clearances shouldnt have to be checks often at all.
But yeh I might just have to do it myself.
 

twisties

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maybe you should print out some of the posts from the threads on this site so he can understand how important it really is!
 

headsmess

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technically, they dont...very low wear items, the valves are.

problem is, cus theyre made in china, cheaply, tolerancing isnt as fine as say...a kawasaki. so while a kwaka might be fine for years with no checking(take my old 1983 gpz750 as an example...), a cheap china bike is cheaply assembled, from cheap parts...parts that tend to wear in and settle down....

after say 100 hours... the valves may never need touching again.... meh...something like that anyways... :p
 

sean01

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it seems the valves in these engines arent really suitable for unleaded, they sink in the valve insert. i have seen them with razor sharp edges on the valve seat....
you could always use that lead mixing oil in your fuel to reduce valve wear....
or just replace with some good quality ones
 

Cactus Jack

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Here's some great info on what causes valves and seats to wear and lose clearance ...

Puma Race Engines Technical Guide - Unleaded Fuel - Part 1

Also remember that most pit bike engines are used on DIRT which has an uncanny tendency to get into things and wear them a lot quicker than they otherwise would ... Extremely fine dust particles can easily make their way thru the pores of foam air filters ... especially ones that aren't religiously kept clean and adequately oiled ...
 

sean01

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yeah the fuel additive im referring to is the same that they use on lpg gas installations in early cast iron headed engines... its a lead replacement oil.... works wonders and slows down the valve sinking effect...

iv noticed on these engines the valve seats are very good but the valves are rubbish...and iv had my doubts about the hardening process that theyv actually been thru...

lpg compatible valve inserts are the strongest and id say the china heads are on par with these..

put a set of stainless valves in and bingo no more valve wear after run in
 

Cactus Jack

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Add to the above post that the air filter and carb are located in an idiot position that just begs for dirt , nud , water and crap to get into the engine ...

Also ask yourself WHY the 4 stroke MX bikes such as YZF's should need any more regular maintenance than a high performance road bike engine such as a YZF 1000 Yamaha (which they are based off) and you'll start to see things a little differently ...

Horizontal engines were originally designed in the late 60's to be run on leaded fuel ... the lead lubricated the valves and seats and virtually eliminated wear ... These days pollution laws have forced oil companies to remove all traces of lead from the fuel and as a result valves and seats don't last anywhere NEAR as long as they used to ...

To anyone who THINKS their engine shouldn't need regular valve clearance checks ... It'd be a good idea to use a Valve Saver additive in the fuel ... AND don't go revving your engine hard or let it get too hot ... And that means run your air/fuel mixtures on the rich side to keep the valves cooler and accept sluggish performance ...

Most cars and Jap road registerable bikes have high quality valves and seats to minimise the wear ... but it's still a lot quicker than it would be with leaded fuel ... Most cars had self adjusting hydraulic lifters which totally eliminated the need for valve clearance adjustments ... Manufacturers HAD to go hydraulic to get people to buy their cars ...
 
H

henry Haataja

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You need new piston rings that hold compression in the top end so if there bad there will be no compression
 

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