Author Topic: 400 Four detonation  (Read 1093 times)

Offline hairygit

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Re: 400 Four detonation
« Reply #15 on: February 06, 2018, 09:49:32 AM »
Good question Drew, I was thinking about that too.

It's something that's not claimed generally by most types of system. They normally go with fatter / hotter spark, improved starting, improved high speed accuracy etc, making it difficult to see if they have considered more in depth issues and completed a design to address something very specific. They appear, in this field generally,  to cover this sort of stuff with words like "improved driveability" which could mean any number of things.

The Boyer has always seemed a very competent system but ultimately it may be worth posing a specific question to them to understand, in their view, how they approach something like this.

It's complicated by the Honda original, in my view, being a very good mechanical design with some clearly very subtle qualities that are very hard to improve without very specific knowledge.
The area that would seem in the original fit to be most influential is the length of spark,  ie duration of the spark event. Honda appear to have designed in a specific length that would benefit their combustion chamber requirements. The bigger is better school of thought may trip up on something like this.

This is pulling together what I view as happening to produce error;  with a still relatively low piston speed at around 2/4000rpm the ignition reaches its maximum advance. The time of piston travelling during the period of spark initiation until piston reaches tdc,  if it's more time than spark duration,  then the spark will have completed prior to tdc. It looks to me that Honda are trying to cover this area of interest by designing in a "long" spark.
If a replacement system shortens the spark,  it looks like this area is the most vulnerable to complications. So anyone claiming a shorter ignition duration will appear suspicious.
It's notable ( I think it's correct)  that Honda delay the max advance rpm point for the 400 Four above those of the 500 / 750 so they are also massaging this point as well to avoid the detonation as I view it. I think the Boyer doesn't change this spec but also uses it for the whole range of these four cylinder engines.
If you then add in that mixture curve that we can see has the possibility of going very lean (peaks about 15.7 parts air to fuel ratio) it all meets at this critical point,  making it very marginal to get a clean combustion event completed.
Ultimately I think the issue is down to allowing the engine to labour at high throttle openings at low RPM, these Honda's are designed to rev, the max power is developed at high revs, and restrained use of the throttle at low RPM in high gear is the answer. If you want to go faster, knock it down a gear or two and let it rev freely.

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Offline K2-K6

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Re: 400 Four detonation
« Reply #16 on: February 06, 2018, 12:53:42 PM »
Agree,  hairy.
Being more informed about why you've got to do that and take account of how they run will avoid giving problems.

It's fairly common though, as discussed, to impose or overlay things like the British bike experience onto these bikes though,  particularly as newcomers to these generally see them all as old bikes with no real distinction or separation of their care.
I was speaking recently to a 750 K6 rider at a bike meet, really nice example. I said it sounded good and asked as to how it was running, he replied that he'd given it a bit of a thrashing on the way there "and took it right up to 5000rpm" which really is nowhere near using the full range.

That fuel trace at the beginning is run in 4th gear,  so knocked down two from top. The essence is, I suppose, that if you find yourself with dropping speed and you continue to open the throttle more with little or no increase it should alert you to back out of it or drop ratios until it does what you ask of it.

Interesting that two more, in addition to Julie's,  have turned up on here with apparently the same issue. Plus the two cylinder heads of 250 /350 engines over on another thread with very close failure type.

It certainly makes a different view of running them on pod types airfilters, and trying to jet them without a dyno facility look easy!   :o (definitely a joke :) ) if it's not understood about the original intricacies,  how can a competent decision be made? Particularly if you change the carefully set vacuum gradient that Honda sent it out with.

I suppose this thread is a bit of a walkthough and illumination of what really affects them.

Offline Drew400

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Re: 400 Four detonation
« Reply #17 on: February 06, 2018, 04:33:47 PM »
Thank you again.

Any excuse to 'thrash it' over 5000rpm sounds good to me.

Common sense tells me to drop a cog (or two) when the power runs out... two-up, headwinds, etc. But that's true of every bike I've owned.... apart from the XS1100 that could torque it's way out of prison!

Cheers, D.
Previous bikes:Puch Maxi 50, CD175, Suzuki T500, CX500, Z200, GS850, XS1100, GT750 (kettle), RD400, GTR1000 (not too many boastables in there!), CB750F2 Phil Read Replica

Offline Rudi45

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Re: 400 Four detonation
« Reply #18 on: February 21, 2018, 03:08:57 PM »
Hello,
i´m new here, but I will post later on in the new member introduction.

Excuse my poor technic English.
I will show you my Dyno run,  direct after rebuilding the Motor with new piston an so on.
I hope you can read this



Drehmoment = torque
Luft, Kraftstoffverhältnis = Air-Fuel
Max. Leistung = Max power

Regards

Rudi

Offline K2-K6

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Re: 400 Four detonation
« Reply #19 on: February 21, 2018, 07:10:38 PM »
Hello Rudi,  welcome to the forum.
Your English is fine and I think much better than German is spoken by us over here. So all ok.

Thankyou for posting your dyno run printout which is interesting as part of the subject discussed on this thread.

It'll be interesting to find out more about your engine and if you have experienced something like the original problems that initiated this thread.

Nigel.

Offline Nurse Julie

  • 1973 CB750 UK K2.1977 CB550/4 Mongrel Brat. 1978 CB400/4.
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Re: 400 Four detonation
« Reply #20 on: February 21, 2018, 07:15:55 PM »
Hi Rudi.
What happened to your engine to make it require a rebuild?
« Last Edit: February 21, 2018, 07:37:03 PM by Nurse Julie »
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Rudi45

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Re: 400 Four detonation
« Reply #21 on: February 21, 2018, 07:31:34 PM »
[ Guests cannot view attachments ] [ Guests cannot view attachments ] Please wait :)

I´m writing on an other PC. It needs time to do in English.

Stay tuned 8)

Rudi

Offline Rudi45

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Re: 400 Four detonation
« Reply #22 on: February 21, 2018, 07:35:44 PM »
excuse for the lot of pics.
But I will learn :-[

Offline Rudi45

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Re: 400 Four detonation
« Reply #23 on: February 21, 2018, 08:10:07 PM »
Hello Nigel and Julie
this is a very long story.
My first  Bike was 1975 a cb 400 four. Two years later I sold.
In the meantyme  I had a lot of different Bikes and a long nothing.

8 years ago I thought about a new, used cb 400 four at ebay.

I´ve done everything  by myself. Only the Motor a specialist had done.

After 500 Km  , when I start the cold engine it smoked blue for nearly 5 minutes.
When the motor reached Temperatur there was nothing.

The specialist changed once more the piston rings. To original Honda!!??

But after 500 Km , the same procedure. Smoking like crazy.

I was so angry, Iwould like to sell this Honda.

Then I had an Idea. In the near of my City is an old Honda dealer, I contacted him.

He has now putted in Pistens, rings.  0,75 .Everything original Honda parts.

I brought him the disassambled Bike. He opend the motor and was looking everywhere.

I hope, now everything is now okay. This bike was until now very expensive. Incredible.

It´s a pity, the weather. Okay it´s winter. Therfore it stands in my flat.

I will put a few fotos without comment.. They show the motor  Inside after 500Km.

Regards

Rudi, now and 1976












Offline Nurse Julie

  • 1973 CB750 UK K2.1977 CB550/4 Mongrel Brat. 1978 CB400/4.
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Re: 400 Four detonation
« Reply #24 on: February 21, 2018, 08:17:29 PM »
Your English is good Rudi. Nice photos, you have not changed since 1976  ;D ;D
Good place for bikes in the winter....indoors 👍👍👍👍👍
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Rudi45

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Re: 400 Four detonation
« Reply #25 on: February 21, 2018, 08:23:40 PM »
Thanks Julie,
in 1976 i was 31 :'(
Mr. Google is my friend ::)

Rudi

Offline Johnwebley

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Re: 400 Four detonation
« Reply #26 on: February 21, 2018, 09:14:10 PM »


  welcome Rudi,enjoy the fun world of sohc.

 back on subject,my 500 had similar issue about 16K miles ago,the piston on the RH outer was chewed,and rings gone,the one next to it,has a broken ring only,piston OK,other two were ok,.

 it was put down to over revving when cold ,maybe detonation,no damage to bores,just one new std piston and 4 sets of rings

  PS,I have emailed Boyer explaining the discussion and asking for the various advance curves and spark duration.

 hopefully they will be interested
lifelong motorcycle rider,and fan

Offline Johnwebley

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Re: 400 Four detonation
« Reply #27 on: February 22, 2018, 05:18:28 PM »

  brief reply from Boyer,basically saying nothing,I am guessing commercial secrets ,but they did refer to the "wasted" spark,
 not sure how that helps? or not .

 
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Re: Advance curve

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Re: Advance curve


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Thank you for your enquiry, sorry we don't publish this information as we have a few secrets that do give us an edge. You may note  that we fire all cylinders every 180deg, this requies a little trickery, but it works.

Regards Tech Dept.




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« Last Edit: February 22, 2018, 05:22:22 PM by Johnwebley »
lifelong motorcycle rider,and fan

Offline K2-K6

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Re: 400 Four detonation
« Reply #28 on: February 22, 2018, 09:26:56 PM »
Thankyou for asking them John, I guess they're in a position that's awkward from a commercial point of view.

No answer either way suggest they don't have one though. I worked with someone who always got hold of a manager when they came out on the factory floor and cornered them with awkward questions. If they didn't give an answer, her reply was "we'll just make something up" which generally made them nervous.

To be absolutely fair, it's a carburettor initiated problem as I view it and asking an ignition system to cope with that error is unlikely to happen in its entirety. The question for any aftermarket supplier is,  does your system with its change in specs,  match / shorten / lengthen the spark duration?
It's a very valid point if we believe it could lead to this type of engine damage.
Hondaman has specifically built his switching to match the Honda original,  that seems to be the most competent answer I've so far seen.

Their (Boyer) firing at 180degree intervals appears related to emissions, I can't see the relevance in this context either John.

In common with Hondaman,  (and by using the 400 advance curve for all the fours)  they delay the max advance for the 500 and 750 a little,  so that may assist the larger capacity examples in this area. Doesn't make make any difference to our little collection of damaged 400s though.

On current engines with knock sensors,  when detonation occurs then the first reaction is to retard the ignition until it stops. It's this that limits performance of high output motors when they are run on lower octane fuel. Keeping them from damaging themselves reduces output.

I cover some more things in next post.