Engine Braking - Honda CRF1000L Africa Twin Forum
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post #1 of 16 (permalink) Old 03-08-2019, 09:12 AM Thread Starter
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Engine Braking

Apologies if I am being thick here, I have realised that I do not know how the engine brake works on the AT. Many engine brakes I have come across have a means of varying the valve timing to turn the engine into a compressor or a mechanical exhaust brake, admittedly most of these arrangements are diesel engines. As far as I can see the AT has relatively simple camshaft drive and valve gear arrangement so I can't see how the retardation has three variations according to the selected mode or what the mode selector actually does.

I would be grateful is one of the experts out there could enlighten me please?
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post #2 of 16 (permalink) Old 03-08-2019, 10:43 AM
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Originally Posted by RayCollington View Post
Apologies if I am being thick here, I have realised that I do not know how the engine brake works on the AT. Many engine brakes I have come across have a means of varying the valve timing to turn the engine into a compressor or a mechanical exhaust brake, admittedly most of these arrangements are diesel engines. As far as I can see the AT has relatively simple camshaft drive and valve gear arrangement so I can't see how the retardation has three variations according to the selected mode or what the mode selector actually does.

I would be grateful is one of the experts out there could enlighten me please?
I’m no expert but was told by someone who also was not an expert that to decrease the engine braking Honda ‘hold open the butterflies’. Does this make sense? I test rode the bike with engine braking last week and found the difference between the levels very subtle but I also now believe that all 3 of them provide less engine braking than on my 2017 bike. But this is entirely subjective and probably wrong
Mike
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post #3 of 16 (permalink) Old 03-08-2019, 12:00 PM
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I've been told the same thing - tickover is effectively increased slightly in higher 2 settings. I assume some electronic jiggery pokery too! (Hmmm....what will our transatlantic cousins make of that phrase!). Pretty sure this has come up before on this forum. Only changed mine coming down a steep and barely surfaced track in snowdonia recently....not sure if it made a difference but I did try descending with out using brake, as per off-road course I did a coupla years ago.
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post #4 of 16 (permalink) Old 03-08-2019, 12:42 PM
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Not sure about the tickover being altered. This is my understanding.
Engine braking is caused by the work required to pull the piston down against a vacuum. This occurs on the induction stroke with the inlet butterflies closed. So if you have 3 settings it means the butterflies have 3 positions when shut - or nearly shut . So for least engine braking they will be open slightly to create less vacuum,The work done is drawing air (no fuel) past the almost closed butterflies.

Get a cycle pump and put your finger over the end and pull it open - the resistance you feel is what we are talking about.
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post #5 of 16 (permalink) Old 03-08-2019, 12:48 PM
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Throttle by wire gone amok! On the 17 the throttle butterflies are directly connected to the twist grip so engine braking closed throttle is fixed.
With electronics the servo motor can open the butterflies with no fuel injection and thus vary the perceived amount of engine braking.
What's the point? I don't see the necessity.
Why do Engineers do stupid sh!te like this? a) because marketing asked for it. b) because it's possible.
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post #6 of 16 (permalink) Old 03-08-2019, 01:56 PM
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Throttle by wire gone amok! On the 17 the throttle butterflies are directly connected to the twist grip so engine braking closed throttle is fixed.
With electronics the servo motor can open the butterflies with no fuel injection and thus vary the perceived amount of engine braking.
What's the point? I don't see the necessity.
Why do Engineers do stupid sh!te like this? a) because marketing asked for it. b) because it's possible.
Well I am used to driving vehicles with no engine braking (my auto car and my Triumph Rocket3), and I much prefer it - I wish they had provided another couple of levels of adjustment on the Africa Twin.
Mike
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post #7 of 16 (permalink) Old 03-08-2019, 04:25 PM
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The absolute best technique for stopping a motorcycle the quickest is clutch in & apply both brakes hard, & if your motorcycle has ABS even better.
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post #8 of 16 (permalink) Old 03-08-2019, 05:22 PM
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The absolute best technique for stopping a motorcycle the quickest is clutch in & apply both brakes hard, & if your motorcycle has ABS even better.
Unless you are on gravel - then ABS on the rear needs to be off or you will skip-hop along for a long way...
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post #9 of 16 (permalink) Old 03-08-2019, 05:27 PM
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Originally Posted by mike5100 View Post
Well I am used to driving vehicles with no engine braking (my auto car and my Triumph Rocket3), and I much prefer it - I wish they had provided another couple of levels of adjustment on the Africa Twin.
Mike
When I wrote the 2017 AT (standard) had fixed engine braking because throttle butterflies are cabled to the twist grip - I should have said it is excellent engine braking. Little need for braking in city riding or on trails to slow down unless you need to scrub speed quickly.
Simple is better.
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post #10 of 16 (permalink) Old 03-08-2019, 05:46 PM
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When I wrote the 2017 AT (standard) had fixed engine braking because throttle butterflies are cabled to the twist grip - I should have said it is excellent engine braking. Little need for braking in city riding or on trails to slow down unless you need to scrub speed quickly.
Simple is better.
Depends whether you want comfort or speed. If you like driving hard then having high engine braking is probably a good idea, but for me the constant slamming backwards and forwards is just tiring. So surely it's better for us to be able to choose how much engine braking we want?
Mike
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