Yamaha SR250 Power and Temperature Testing

JadusMotorcycleParts

Active Member
I guess the next big questions are, is this normal? OK? Optimal? What would be optimal?

With regards to head temperatures here's so much discussion on the subject on various motorcycle forums and so much miss-information out there. Especially from forum 'gurus'. I like to get information from as reliable sources as possible.

I found this great diagram about air-cooled aluminium engines and the relationship with temperature and strength from the book by Pratt and Whitney called 'The Aircraft Engine and its Operation'. I actually found it in a post from a guy on a motorised bike forum: http://motoredbikes.com/threads/maximum-safe-cylinder-head-temperature-cht.40994/

I trust a diagram like this. Pratt and Whitney engineers would have known their stuff.

This means that with the SR's head temps getting to 214C on the highway in 26C heat its in the safe zone, but what would the head temp be on a hotter day? In warmer climates than Sweden's pathetic summers? Maybe the carb would just need to be jetted richer... Attached is another cool diagram showing the relationship between rich/lean conditions, temperature, power and economy.
 

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JadusMotorcycleParts

Active Member
And with regards to oil temp, there is an equal amount of misinformation out there, so I have been reading up on my bible by A. Graham Bell again. Here is an extract:

'An engine should never be driven hard until the oil reaches 70C, while the ideal operating temperature is 95-110C. It can go as high as 130C for short periods, but oil breakdown and excessive oxidation will take place above this temperature. In a race engine, bearing failure is a possibility any time the oil temperature goes past 130C, and generally, HP is lost over 115C'.

Again, the SR is pretty safe here, but if ambient temps were higher, head winds stronger and hills steeper, perhaps these temps would be exceeded...
 

JadusMotorcycleParts

Active Member
Before I did some more testing yesterday I installed the oil pressure gauge - in place of the temp sensor post oil filter. Really interesting!

I sure am glad I did some reading about the different oil pressures of plain bearing engines vs roller bearing engines before I installed it. Otherwise I might have been very concerned!

Results:

From cold <50C
Idle: 2-3psi
On road (3-6000rpm): 9-12psi

Operating temp >90C
Idle: <0.5psi (pretty much unregistered on gauge)
On road: 0.5-1.5psi

So there you have it. Very similar readings to what others have documented on Yamaha engines with roller bearing cranks. No wonder they nickname these things 'worry gauges' though. Absolutely best not to install one haha - just an unneeded distraction on the bike.

Btw, has anyone else seen or heard of another person to have installed an oil pressure gauge on an SR250? I'd be curious to see if they got the same findings.
 

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JadusMotorcycleParts

Active Member
I have been discussing the temp testing scenario with my girlfriend - who is a mathematician come software engineer. The conundrum, as mentioned earlier, is the number of variables in the equation. She gave me some really good input though - with that many variables, the best thing you can do is take a lot of samples and average them out. Makes a lot of sense. Just do the same test many times in many different conditions with different riding styles and try to establish a more reliable/stable baseline (in comparison to one test for the baseline). I'm happy to do this because it just means more riding! ;D
 

coyote13

New Member
I would have to agree with your girlfriend/matrhematician. Operating in a completely controlled environment will give you a great deal of accuracy at a fixed point, but only for that fixed point, resulting in a static set of data which will not account for differing conditions, riding styles, or even different static throttle input. What you need is good dynamic data, reached by averaging the data from a number of conditions.

Edit: If you included a dyno-style setup you could do this indoors in a very controlled environment, and still get dynamic data since you would be able to actually run the bike under load
 

cosworth

New Member
This engine needs as much oil as it can get up the head bolt passageway to the cam. To the point that I overfill my sump a bit and change the oil often.

These numbers jive with the temps I get from my Ducati monster that is air cooled and has an oil temp gauge. I'd say it looks good.

To maximise the oil feed to the cam we need flow, pressure, and optimal viscosity. The flow can only be helped by drilling a small hole through the access bolt from the head bolt shaft to cam bearing. And drilling the cam holes a bit as well. This changes flow but affects pressure, of which there is very little. And every SR250 motor should have the flow limiting roll pin in the crank too.

So really that leaves viscosity. Or quality of oil. Which is a subjective can of worms.

The real solution long term for anyone running this motor is for there to be a roller tappet. They are available for the SR500 but do not fit. I have contemplated making a prototype but it would be my biggest engineering feat to date. I'm not that fancy.

Drill head, good oil, roller upgrade. That could keep these motors running for 50-100 years as long as people keep making XS650 pistons which are the same.
 

JadusMotorcycleParts

Active Member
coyote13 said:
If you included a dyno-style setup you could do this indoors in a very controlled environment, and still get dynamic data since you would be able to actually run the bike under load
Yeah I think getting some good dynamic results will be good. I'll write everything up in a spreadsheet to be able to analyse and compare later.

But yes, doing the same test on a dyno or 'rolling road' would be a good way to get a pretty controlled environment and be able to do back to back tests to get a stable result/comparison. :D
 

JadusMotorcycleParts

Active Member
cosworth said:
Drill head, good oil, roller upgrade. That could keep these motors running for 50-100 years as long as people keep making XS650 pistons which are the same.
Thanks for the input man. Always appreciate stuff from people with experience/who have tried and done some tests themselves. Really valuable! Cheers.
 

JadusMotorcycleParts

Active Member
Rummaging around in some old parts bins and found this from an abandoned project! New Barnett clutch with stronger springs! Guess I'll try the XT250 clutch on the next bike :D
 

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JadusMotorcycleParts

Active Member
I decided it would be worth while testing the use of an oxygen sensor with an air fuel gauge to take the guesswork out of jetting - especially if I want to test all these different parts. Its not a cheap set up, but I figure its a worthwhile investment if I'm wanting to get the jetting spot on, be able to give jetting guidelines for others, and for when I work on any other bikes in the future - for example this xs750!

I had some perfect size tube lying around that fit into the end of these reverse megaphone exhausts, so I welded the bung into that (ignore the shit welds, its airtight ) and I will do as I have seen others do and attach this set up to different bikes with some large ss ring clamps. Seeing as it is only ever meant as a temporary thing just to get the jetting right at the completion of a build. We'll see if it works and is a useful tool shortly!

 

JadusMotorcycleParts

Active Member
I have been riding the bike quite a bit the last month and documenting the temperature readings - lengthy posts to come.

I never got round to replacing the clutch, but the problem seems to have disappeared nearly entirely... Could it be that putting this new tech oil in the bike cleaned out a lot of gunk that eventually got caught in the plug trap and the filter? And now it is grabbing like it should again? Who knows. Will still need to be done down the road probably ::)

Anyway, I installed the finned valve covers for some testing to compare to the stock temps. I think they look really cool 8) Especially if the engine was tidied up a little. Some food for thought though, the exhaust valve cover is shrouded by the frame down tube. I might mock up a scoop out of sheet metal in the future to route cool air better to it. For now, testing will be done without it to keep things consistent.
 

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JadusMotorcycleParts

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I calibrated and hooked up the O2 sensor and the air fuel ratio meter today on the XS750 I am tuning. Everything worked great! The kit I mean, not the bike. Was running pretty lean, much tuning to come.

Anyway, this will be the set up I use to get everything dialed in perfectly for the SR. I cant believe how awesome of an investment this is! It will save so much time and guess work :)
 

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teazer

Active Member
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JadusMotorcycleParts said:
I calibrated and hooked up the O2 sensor and the air fuel ratio meter today on the XS750 I am tuning. Everything worked great! The kit I mean, not the bike. Was running pretty lean, much tuning to come.

Anyway, this will be the set up I use to get everything dialed in perfectly for the SR. I cant believe how awesome of an investment this is! It will save so much time and guess work :)
Nice Innovate gear. I use a similar gauge coupled to a PL1 data logger and with Aux box and TC4.

That Lambda sensor is too close to the end of the pipe and will read lean. What we often fail to realize is that an exhaust pipe pulses several times in each revolution and as it does that it sucks air into the tailpipe which makes it read leaner than it really is. Get another bung and weld it it in just in front of the muffler or into the muffler body pointing up and under the motor, so it is invisible and cap it after setting the jetting.
 

JadusMotorcycleParts

Active Member
I know you're right teazer :) It is not in the optimal location... perhaps far from it.

Although the reason is two fold, I want it to be portable/removable/re-usable on different bikes, plus I dont want to weld in a bung in an exhaust system that is later not going to have an O2 sensor mounted.

The O2 sensor actually reads fine as soon as the bike is off idle and there is enough exhaust flow. As long as I ignore the false lean readings at idle and just continue to tune the pilot circuit up to 1/8th throttle and then all the way through, I think it will be much more accurate than plug chopping. To get the idle mixture/setting right I will just use old school methods ;)

I also figured if Innovate sell and suggest using this thing, there cant be too much wrong with my set up?

https://www.youtube.com/watch?v=WiZxAL_ua7M
 

JadusMotorcycleParts

Active Member
I am going in to a different mechanic next week who has a dyno and will try sort out a time to test the exhaust etc, the other guy was dicking me around a bit.

In the mean time, I got sick of riding this bike around bone stock. So I finally got round to filming some instructional clips for installing the seat and the great outcome of that was... The Jadus Euclid SR250 Seat is now installed ;D Just goes to show what a drastic impact it has on the bike with the seat alone. Now I'm pretty stoked to be riding this around, despite the ghastly tail light and blinkers.

Installing the seat highlights the mounting angle of the tank - being on a rearward slant. Next thing to install... The Jadus Tank Leveling Kit! Will sort that tank position right out. Then perhaps a frame loop and some blinkers and a nicer tail light.
 

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JadusMotorcycleParts

Active Member
Looks like the 'hot' summer weather in Sweden is over for this year :'( We had a couple of weeks of high 20's and even pushed 30 a couple of times. But now we are coming back down into the low 20's and teens. On a few of those hot days however I managed to run some back to back tests of the stock valve covers vs the finned ones. I collected data on a few other days as well when the temps were in the lower 20's. I have it all plugged into a spreadsheet but I am still trying to figure out the best way to present it - how to lay it out. In the meantime, here is one hand written table from one afternoon of testing...

I would be confident in saying that the finned valve covers definitely do something. There is a noticeable, consistent difference in peak oil and head temperatures. How much? Not much. I guess I was hoping for a solid 5 degrees or more difference but that was probably optimistic for a part that contributes to less than 5% of overall engine surface area! The idea though was that there is a lot of oil that quirts from the cam shaft past the rockers and collects/pools in the valve covers before draining back to the sump. Anyway, the actual difference was consistently 2-3 degrees cooler with the finned covers in both the oil and head temps than the stock ones. While the actual temperature of the parts themselves was around 15-20 degrees cooler.

So depending on oil grade/quality and oil temperatures, these covers might help the engine stay inside the oils ideal operating temperatures and away from any temps that would start to break down the oil faster.

All in all, I am somewhat satisfied. Now gotta work on developing and testing the oil filter cover cooler!
 

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JadusMotorcycleParts

Active Member
I have been real busy the past couple weeks getting everything ready for dyno testing. At the same time I have been making some installation vids for some of the parts:

For example: https://www.youtube.com/watch?v=pBB7CTFvWqc
 

JadusMotorcycleParts

Active Member
All the performance parts bolted up pretty easy and I have a few different things I wanna try out - if you have been following my other build thread you will know, but I'll post again here too.

The exhaust is mostly a fixed thing, although I will try different methods in the silencer only to affect back pressure slightly.

The ignition advance brackets are also fixed - at 5-6 degrees extra advance. These will either work or not work.

Then I have 3 different length intakes I want to try to see what affect they make - see attached.

You can also see the bike as it stands today with all the gear on ready for testing. Notice the tank levelling kit is not installed yet ;) ;) That will come when I make a video for installing it.
 

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