Compression ratio, ignition timing, CHT & EGT measuremen

[James P]

From available info, the ignition timing on a KR1 reaches up to 25 degrees BTDC, before retarding from 5600rpm onwards. From other available info, I have calculated the geometric compression ratio to be about 12:1.
From experience with air-cooled bikes (although not particularly well cooled!) using 95 octane pump fuel, figures like these can be responsible for holed pistons . As such, lowered compression, careful setting of squish clearance, retarded ignition and monitoring of CHT & EGT is the best way to ensure freedom from heat-related damage.

I presume that the water-cooling will moderate the temperature and keep it more consistent, but would be interested to know if anyone has had experience with CHT & EGT measurement on a KR1. The method of CHT measurement I have used is a thermocouple washer under the spark plug seat.

As I am yet to gain any practical experience with the KR1 (see my "Hello & thanks" post in the Chit-Chat section), can anyone offer any advice regarding CHT & EGT readings during normal running on a standard-ish KR1 (or even any KR1 or KR1S)?

I would be particularly interested in the KR1/1S running experiences of forum members in Australia, but any input is welcome!

Thanks in advance,
James

[dave32]

I think there's a bit of confusion with the C/R's quoted for most things,it doesnt always mention what formula was used to get it.
The KR1 is quoted as 7.4 to 1 in the manual,my 93 TZ250 is 8.3 to 1 as stock which is designed for 100 octane Leaded at minimum.
I think some of the aprilia 125 Gp bikes had compression ratios of over 16.1 when using the other formula that you have used (to get 12.1).
kr's dont generally give any trouble on stock settings but they can vary wildly from engine to engine,best thing to do is get the squish clearance down to 0.7 mm and make sure that both barrels are the same length,its not unknown for variation between the 2.
i think it would be okay to raise the CR to 8.0 to 1 max if you plan on using only super umleaded or something with a octane rating of 98 or above,manufactures play it safe with timng/jetting and C/R as they dont know what fuel you can get locally and where you live (altitude etc) or how you ride,a guy who potters about could get away with leaner jetting and more advanced timing as an example.

[James P]

Thanks for your input Dave. I always like to convert to geometric compression ratios, because it takes exhaust port height out of the equation. Although I understand the concept of corrected ratios (which I think are used by all Japanese makers), I am not experienced enough to use them for comparison purposes. Besides, if corrected ratio is truly "correct", the real engine capacity of a KR1 is only about 142cc!

When I finally get my KR1 and put it on the road, I will be using a CHT & EGT gauge on each cylinder. I will keep the engine spec standard for the time being (except maybe for some resonator chamber spacers!) and get some experience with the running temperatures. I wholeheartedly agree with your suggestion to check cylinder heights and squish clearances - if/when I dismantle the top end for inspection, I will be sure to do this.

I am still a bit wary about the factory settings for ignition timing and compression ratio, because these bikes were released when ordinary pump fuel quality and consistency was (generally) a bit better than it is now!

I'll see how it goes and report back if there is anything to tell.

Regards,
James

[Luders]

One thing I will say about the cooling is, it's adequate on a standard engine in Britain.

If you are going to be getting more from the engine and obviously running in a warmer climate, I would suggest upgrading the radiator.

[James P]

...If you are going to be getting more from the engine and obviously running in a warmer climate, I would suggest upgrading the radiator.

Thanks for the tip Luders. I plan to leave the engine fairly standard (i.e. carbs, pipes, porting) and am gaining the impression that the "high" compression and "advanced" ignition timing are compensated for by the vastly superior cooling (its been fifteen years since I owned a water-cooled bike!).
I'll get a better impression once I have the bike on the road with the CHT & EGT gauges fitted. I'll try to report back once I have experience with the temperatures obtained through a variety of riding conditions, although this may take a few weeks...

Regards,
James

[dave32]

Hi james,
Just some thoughts on EGT,
You will still need a "base" setting to work from as to what temp suits "your" engine for best performance,this will involve plug chops/head/piston crown burn pattern/colour etc.
the stock settings arent "far off" in most situations/conditions,you may be able to drop a Mainjet size in the "warmer climate" to get the best from the "top end" but midrange and throttle response can only be set by "rider testing" to see what works best for you.
if you were building an out and out racer and going radical on the tuning then an EGT will be of use (once you have a base setting to work from) but for a road going machine i cant see any actual gains.
cheers
Dave

[TwoStroke Institute]

From available info, the ignition timing on a KR1 reaches up to 25 degrees BTDC, before retarding from 5600rpm onwards. From other available info, I have calculated the geometric compression ratio to be about 12:1.
From experience with air-cooled bikes (although not particularly well cooled!) using 95 octane pump fuel, figures like these can be responsible for holed pistons . As such, lowered compression, careful setting of squish clearance, retarded ignition and monitoring of CHT & EGT is the best way to ensure freedom from heat-related damage.

I presume that the water-cooling will moderate the temperature and keep it more consistent, but would be interested to know if anyone has had experience with CHT & EGT measurement on a KR1. The method of CHT measurement I have used is a thermocouple washer under the spark plug seat.

As I am yet to gain any practical experience with the KR1 (see my "Hello & thanks" post in the Chit-Chat section), can anyone offer any advice regarding CHT & EGT readings during normal running on a standard-ish KR1 (or even any KR1 or KR1S)?

I would be particularly interested in the KR1/1S running experiences of forum members in Australia, but any input is welcome!

Thanks in advance,
James

On a water cooled engine CHT is useless. EGT is directly proportional to ignition timing and compression So you maybe lean with 500C and still rich with 650C depending on your set up.
What is your aim? If that isn't wringing everylast 0.25HP out of the engine you won't have to worry about EGT, CHT or water temp. EGT is only really useful at WOT as well, no meaningful info will come from riding round in peak hour.

[James P]

Thanks for the comments. My aim is to firstly establish what "normal" (or at least "as found") running temperatures are, then assess the effects of minor jetting changes on EGT and the feel of the bike on the road.
Once I have suitable settings, I plan to just monitor the temperatures in an attempt to guard against damage due to bad fuel, air leaks etc. (it may be too late to prevent this damage by the time I feel the difference in performance ). This procedure has proved very successful in the past, although admittedly on air-cooled bikes.
I am surmising that thermocouple washers under the spark plugs will show changes in temperature much quicker than the water temperature gauge and also allow me to ascertain any differences between the two cylinders.
I never had any problems with the water-cooled bikes I owned 15+ years ago (RD250LC and RG500), but perhaps I was just lucky!

Regards,
James

[dave32]

I doubt it was luck (with the elsie and gamma),probably had more to do with they were looked after
I dont even run EGT on my TZ250 or RS125,once you have a base setting (from taking notes of conditions and plug/head readings) i just change accordingly (to the conditions,weather,track type),on my tuned B2 i do the same,the most i ever need to change is a size or 2 on the main (between winter/summer) on the KR.
one thing i would say is that using a decent oil is more important on a kR than it was on say an elsie(which you could use Semi/mineral types with no bad effects).The KR NEEDS fully synthetic (or a decent castor/synthetic for track use),run it on a crap oil and it wont last.
Cheers
Dave

[TwoStroke Institute]

Thanks for the comments. My aim is to firstly establish what "normal" (or at least "as found") running temperatures are, then assess the effects of minor jetting changes on EGT and the feel of the bike on the road.
Once I have suitable settings, I plan to just monitor the temperatures in an attempt to guard against damage due to bad fuel, air leaks etc. (it may be too late to prevent this damage by the time I feel the difference in performance ). This procedure has proved very successful in the past, although admittedly on air-cooled bikes.
I am surmising that thermocouple washers under the spark plugs will show changes in temperature much quicker than the water temperature gauge and also allow me to ascertain any differences between the two cylinders.
I never had any problems with the water-cooled bikes I owned 15+ years ago (RD250LC and RG500), but perhaps I was just lucky!

Regards,
James

If you don't have a big box of holed pistons you haven't been trying either

A air cooled head has no buffer to temps like a water cooled head has, under plug temps will be slow to react with a water cooled head, ie the exact opposite to a air cooled head which will show a marked ride even under a 20 sec pull on a dyno.
If you want to find differences take it to the dyno. Leaner will fell faster up to a point and one jet should make 50deg F change in EGT.
Hate to harp on it but you won't get any meaningful data on the road unless your holding at least 140 on the freeway, EGT is for WOT not part throttle.

[500bernie]

I love reading this type of technical post, it just reminds me how little I know about what is supposed to be a "simple two stroke engine".
Keep posting.........I may learn something [-o<

[Binetta Steve]

Bernie up until today i thought "Wot" was when you were not sure! Now i know its for wide open throttle. Little did i know how little i knew about KR engines!

[dave32]

TSI is a goldmine of useful info.

[TwoStroke Institute]

Not really Dave I just have limited amount of space in my head and need to get rid of some prior learned knowledge in order to learn something new

[daz680]

I'm with you Bernie, I can pull anything apart and rebuild it, be it an engine or machine and have natural ability to understand how it works from an engineering perspective but this thread is amazing and I haven't got a clue what their talking about