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Offline Terry Ryan

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Re: Starter Motor
« Reply #240 on: January 21, 2021, 09:57:35 PM »
I've had the hot start issue with my 2015 XRX for a couple of years, only occurs after stalling the bike when very hot from ambient temperature (30c +) & slow speed riding, always fixes itself after 4-5 minutes cool down

Offline D6864

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Re: Starter Motor
« Reply #241 on: January 22, 2021, 05:35:09 PM »
*Originally Posted by Javaman [+]
Its due to an increase in the "dynamic compression ratio".
When the bores are hot, the cold air drawn into the cylinders is heated by the residual heat from the cylinders and this causes a significant increase in compression compared to a cold engine.
The reduced friction resulting from warm oil will offset this to some extent but the combined effect of both is to give about an 18% increase in cranking force required. The guy who posted didn't state how hot the engine was or how long it had been turned off but from reading his post, I would expect he had it idling for a while to get it good and hot and conducted the test within a minute or two.
All he did was remove the crankcase inspection plug and stick a socket on the nut on the end of the sprag and with a digital torque adapater attached, measured the amount of torque required to just turn the engine over "by hand"
That makes sense, thanks for the explanation  :028:
I've had hot start issues too, but not so bad that I've had to do anything about it yet


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