knock knock

[4corsa]

I've read a few past posts on the valve knock issue , but haven't seen any that address why this is a problem with a relatively low compression ratio engine. For example, my 749 has a compression ratio of 11.7:1 and my old 2003 R6 had a compression ratio of 12.4:1, yet neither of those had any valve knock with 93 octane gas. I thought octane rating needed to be higher for higher compression engines to avoid knocking. Obviously there must be additional factors.

 

My Scura has always knocked under heavy acceleration. Last year I found a shop that sold Cam 2 105 octane, and when i add a gallon to my tank get no knocking whatsoever. Recently, i discovered Torco Accelerator and add just 4 oz. To a full tank to eliminate knocking - good stuff, and is NOT an "octane booster", but concentrated race fuel.

My recent addition of a K&N filter and Mistral exhaust seems to have made the knocking worse with straight 93 octane (not to mention some new flat spots under acceleration- no surprise), so per suggestions of some posts, ive ordered a PC III and will use the map for Mistral slip-ons to richen the fuel

mixture. I've had good success with this on other bikes. 'wondering if this will help the valve knock situation as well?

[docc]

. . .  and my old 2003 R6 had a compression ratio of 23.4:1. . .

Diesel Yamaha?

[4corsa]

Sorry -thumb stumble. Thats 12.4:1(original post corrected). Thanks.

[Tom M]

If your engine is pinging under load and you're sure that your mixture is good it could be due to carbon buildup on the pistons and in the combustion chamber.  I posted my experience in trying to cure pinging in the 'have another quart" thread.

 

:2c:When you get the PCIII try the GH67 map in the fileshare section.  My bike runs really well with that map along with the stock 02 ECU, Guzzi Ti exhaust, and modified airbox lid.

[4corsa]

Thanks Tom. I read your Have Another Quart thread. I'll be able to adjust the mixture with the PC III and will experiment with some different fuel maps to make sure its running rich enough. I do believe its currently running a little lean with the extra air flow its now getting.. My Scura has 17,000 miles so i'm hoping carbon build up isn't a problem, but it wouldn't shock me. I'll have a look at the top of the pistons, but i will say the spark plugs looked great when I changed them this spring. I've always wanted to put it on a maintenance schedule of Techron (works great in my cars), but really want confirmation from someone who has done this regularly that it doesn't cause any problems.

[emry]

Detonation has much more to do with combustion chamber shape and mixture swirl than the actual ratio. Considering these "hemi" heads are new technology for the early 1900's is it not a surprise Although the "pent-roof" has been around almost as long it seem to work better  . You can tune around it but it takes some work. Yamalube Engine Med is Techron without the gas added, use as directed. My Scura knocked its way home from the dealership.

[4corsa]

Thanks Emry - I just read that Yamalube Engine Med Rx is the new version of their Ring Free that I used to use on my R6. Great stuff - I just ordered some.

[Tom M]

My Scura has 17,000 miles so i'm hoping carbon build up isn't a problem, but it wouldn't shock me.

My bike pinged badly when I bought it with 7k miles on it. I fattened up the mixture in the "ping zone" with the PCIII but I couldn't eliminate the pinging altogether until I did the piston swap mentioned in that other thread.

 

Please let us know how you make out with the Yamalube product.

[motoguzznix]

Hi

 

When the engine pings, it is better to address this in the ignition map. Pre ignitioin must be reduced in the rpm and TP area where pinging occurs. This can be done with Guzzidiag. Mark your throttle grip to find out the tp position.

[docc]

Kevin Cameron, in a recent edition of Cycle World, clearly differentiated between "detonation" and "pre-ignition." I always thought they were the same, but apparently not.

[Bjorn]

This can be fixed. All the things mentioned here can affect "pinging". You indicate that the fuel !mixture might be off. Get this sorted out first, do it yourself or gget it dyno'ed.

 

I only noticed my bike detonating slightly under heavy load recently. Here is a summary how i fixed it. Detailed versions comes later as im off for 4 days riding

 

Get the guzzidiag and tunerpro software. Read all the topics and learn the basics. Next you want to find the "range" where you notice detonation. This is a mix of throttle pos. And rpms.

 

Use guzzidiag as a dashboard to make a scale of the physical throttle position vs the digital one. Should look like this:

 

Next you need to make testrides with normal fuel in order to summon the detonation. I did this in higher gears. When you get detonation mark the throttle pos. And rpm range. You will need this data to adjust the timing with tunerpro/guzzidiag.

 

You want to ignite closer to the tdc. In my sit. I only needed to reduce the timing 1 and some locations 2 degrees to cure the detonation.

 

Ill post details later, im off riding first;) o btw, its not rocket science, just need to take your time

[czakky]

 o btw, its not rocket science, just need to take your time

pasta rocket science...eh?

[emry]

Pasta science or not, motoguzznix and bjorn are right. Ignition tuning is the best method of reducing "knock". Knock or detonation occurs after the ignition event, change the ignition event and presto, smiling happy riders. Short of a decent datalogger the tape on the bar method works, not recommended on modern roads in most locales though. 

[Skeeve]

I've read a few past posts on the valve knock issue , but haven't seen any that address why this is a problem with a relatively low compression ratio engine. For example, my 749 has a compression ratio of 11.7:1 and my old 2003 R6 had a compression ratio of 12.4:1, yet neither of those had any valve knock with 93 octane gas. I thought octane rating needed to be higher for higher compression engines to avoid knocking. Obviously there must be additional factors.

 

Well, do you want the short version or the long?

 

Short version: those other bikes you mention are 4v/cyl engines with the sparkplug in the center; Guzzis are 2v/cyl w/ the plug off to the side. They're also much newer designs: our beloved V11s are essentially a couple of cylinders whacked off a WW2-era aircraft radial, without all the redundant/safety systems.

 

Long version: go check out Harry Ricardo's _The High Speed Internal Combustion Engine_: it's only 90 years old at this point, & clearly explains the answers to all your questions.

 

 

 

My recent addition of a K&N filter and Mistral exhaust seems to have made the knocking worse with straight 93 octane (not to mention some new flat spots under acceleration- no surprise), so per suggestions of some posts, ive ordered a PC III and will use the map for Mistral slip-ons to richen the fuel

mixture. I've had good success with this on other bikes. 'wondering if this will help the valve knock situation as well?

 

Not so much.  It may add enough fuel to reduce the tendency to knock, but then your mileage will go to . As already pointed out above, the best way to cure knocking is to adjust timing advance [failing of course, proper combustion chamber design in the 1st place, as per Ricardo! ]

[4corsa]

Thanks Skeeve for addressing both my questions!