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 Post subject: service intervals in hours or miles.
PostPosted: Sat Mar 04, 2017 2:26 pm 
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Seen a few posts recently about service intervals.

Most true trail bikes, DR,DRZ,CRF250L,TTR,XT,KLR etc) list their servicing in miles. They are sold as dual sport bikes and usually come with warranty.

Nice and easy and you know where you stand but what about the enduro bikes that list the servicing in hours?

Well, one thing to consider is, that when you look into the servicing of these machines, is it the servicing intervals for bikes being used for "mx" or "enduro".
Why is this? In an mx race the bike is (if your a good/expert rider) always on the limiter, having its neck wrung. For an enduro rider the time on the limiter is a lot less and a certainly not bouncing the valves as you would be getting air on a table top during a MX race.

FACT. its REVS that kill engines.
An explanation of this was confirmed to me last year. At the Monaco classic F1 GP the organisers set the engine rev limit at 12500 rpm for the v8 DFV engines used in most historic F1 cars. One client asked if this would be ok as usually for classic events the limit was only 12000rpm. (he was worried, understandably so when an engine runs in at £200k. I asked the engine builder who obviously knows a lot about this and he said his engines were good for 13250 rpm but back in the 70s in qualifying trim they would run 14000 rpm. He then went on to explain this.

At 12000 rpm the engine will do a season before needing a refresh,
at 12500rpm they would be refreshed half way through a season,
at 13250rpm they would last one race and be refreshed
at 14000rpm they might just about last a 20 minute qualifying session. Using 2 engines in qualifying was not unusual in the 70s.

So we can deduce from this that it is the peak revs that cause the damage and wear. By lowering the limit 500rpm you significantly increase its reliability.
Things like valves and conrods are under huge stress at high revs and as all metals do, they stretch. The extra few thou of conrod or valve stretch at peak revs can therefore cause the piston to hit the valves. (or head) not good. At max revs things can fail very quickly.
But you see by reducing the rev limiter by 1000 rpm you have a seasons racing, compared to a day. (You may hear a big end start to go or a cam chain get rattley on your trail bike and stop and repair it before total destruction ensues. If it lets go at max revs its gonna be total destruction.)
Everything has a service life before you enter unknown territory. in the unknown zone it could last for ever or fail in the next 20 seconds.

As most trail riding isn't (or should be) done flat chat on the limiter, the engine is far less stressed than it would be in the hands of a World or European top flight rider.

So when a manual says, for mx piston at 25 hrs for enduro piston at 50 hours, this is based on a good expert riders thrashing it to death. As a pure trail rider you can double or quadruple this.

Then consider oils. In race scenarios with sponsored rides, cost isn't an option. the manufacturers want you to use the recommended brands so when they say change oil at 4hrs for mx or 8 hrs for enduro again you can double or treble this if all you're doing is light trail. (that said oil is cheap compared to engine components so if you stick to their recommendations your engine should last even longer!) Again at higher temperatures and loads the oils break down more than they would for "Trail use" They get thinner and lose some of their friction reducing properties. All things that when they happen, can increase engine wear exponentially.

Also the manufacturers are covering themselves. Riders blowing engines, is bad publicity. Setting the intervals low ensures that failure should never occur, if they are adhered to.

My last bike, a husky TE310 xlite engine was available with 2 year warranty. if kept stock its intervals were in the 1000s of miles for oil and 4000 or so miles for piston. However, If you removed the cat, plugged in a resistor in place of the lambda sensor to open up the ecu fuel maps and removed a throttle restrictor you then reduced the servicing to 40hrs piston 8 hrs oil, 80hrs crank/con rod. All because you had moved the rev limiter up and released a few extra donkeys.

Back in the early 2000s I was going to buy a CRF250. but looking at the "piston at 40 hrs" quote I decided that this was no good. 40 hours is only 5, 8 hr rides! A new piston every 2 months, sod that!

However having learnt more about engines, oils etc over the years I can see how this isn't really the case. There are hundreds of ktms, Hondas etc out there with 150 hours all running sweetly on their original pistons, why? Because they've been used as trail bikes and looked after, and probably have never seen the rev limiter.


So don't get too hung up on engine hours servicing when buying a new bike, if you look after it, it should last you fine.

That said you will need to be extra careful buying a second hand machine as you will not be able to say for certain what its previous owner(s) rode like or how well he maintained it. THERES A REASON WHY EXPERT/SPONSORED/PRO RIDERS OFF LOAD THEIR BIKES EVERY 6MTHS. hence why there's always 40-80 hrs, 6mth- 1year old bargains to be had.

A well maintained bike will last as good as any other. And if you keep 1000rpm shy of the limiter (short shift gears and don't unnecessary rev it to the max) then 50 hours life can easily be 150 hrs.


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