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Author Topic: Yamaha SR250 Power and Temperature Testing  (Read 23186 times)

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #10 on: May 20, 2016, 04:53:19 »
I've only been for very short rides so haven't really got it up to full operating temp properly yet but the gauges are pretty cool - especially the head one which has a max reading that resets ever few hours - so you get a max reading for each separate ride.

What is really interesting is that the oil looses between 9 and 12 degrees from its journey from the sump to the oil filter... Always.  You can see this in the above picture.  I guess the entire engine/crankcases acts like a huge aluminium heat soak.  Kinda cool.  I double checked this by swapping the sensor plugs so the gauges were connected to the opposite sensors and I got the same readings.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #11 on: May 20, 2016, 05:01:08 »
At the same time I bought the temp gauges/sensors, I also bought an oil pressure gauge.  An automotive one.  How foolish.  These engines have roller bearing cranks and cams and therefor operate on very low oil pressure but with a high flow rate.  I knew this too.  Plain bearing cranks, like in cars and many multi cylinder bikes require A LOT more oil pressure.  Therefor, an automotive oil pressure sensor and gauge like the one I had doesn't read anything below 10psi!  Because that would be dangerous for any such engine.  I realised that installing this would be pretty pointless because I have seen XS650s run anywhere between 4-7psi and all the way down to 1-1.5psi when hot.  The same with Harleys apparently.  Thats why they call them worry gauges and advice people not to install them - cos you just end up getting distracted and worried looking at it while riding in the heat.

Long story.  Anyway, I bought a proper low pressure gauge that will read from 1-15psi and I am hoping to install this instead and get some readings - hot, cold, low rpm, high rpm etc.  In the photo you can see the backup earth I installed on the temp sensor as well.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #12 on: May 24, 2016, 02:55:57 »
Got out on the test bike over the weekend and recorded some temperatures.  It takes quite a while for the bike to get up to temperature, which I guess would be the same for most air-cooled bikes.  Outside temp was 18C.  Head temp on a 100kph highway peaked at 198C while oil temp got to 95C in the sump and something like 83C at the filter.

The cheap oil filler cap temp gauge was sitting on just a touch over 80C - which is pretty close to what the oil was after the filter - and perhaps the general temp of the crankcases.  Not so bad after all!

I have been speaking to a local bike shop with a dyno and will hopefully test some of the performance parts in the second week of June when he has a little more spare time.  Sweet!

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #13 on: May 30, 2016, 18:05:04 »
Before I go into the next massive post I will write, I thought it was important to mention oil...  When I did the service on the bike I changed the oil (obviously) and filled up up with some new fancy shit - you could say that I got 'sold' it by one of the local mechanics.  It is this Fuchs Silkolene Comp 4 10W-40.  Just as a side note, the Yamaha manual recommends SAE 20W/40 type 'SE'.  In the past I have used this and have actually tried several others (which I cannot remember) based on recommendations, all of which worked fine.

Anyway, this new oil makes gear shifting really nice - it shifts smoother and more precise than it did before (maybe not saying much cos the oil was nearly black anyway) and the bike seems to run real nice.  However, as many have discussed for long periods of time about synthetics in an old bike...  the clutch now does slip from time to time right on the power band when shifting sometimes - right around 7000rpm where the most power is.  There could be a few reasons for this, one, and perhaps the most obvious - its the damn oil - it just doesn't work with old bikes - something with the clutch plates needing something that the old mineral oils provide.  Yep, could be as simple as that.  Or, another reason could be that this problem may have been there before and I just didn't notice it because the engine was running pretty rough and wouldn't quite make enough power to do it.  OR, the clutch plates were/are actually worn and this new oil with friction modifiers etc just highlights the issue much more than a mineral oil would.  I have read this in a few different forums as well.  Either way, I think I like the oil and I will replace the clutch plates and springs with the next oil change and see how that works out.  They'll certainly need to be stronger if the bike is going to make any more power than stock ;)

Offline cosworth

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #14 on: May 30, 2016, 21:32:28 »
Put the clutch plates from an xt250 in there. A bit thinner steel plates but more of them. Nice grab and shift.
1981 SR250 café hot rod (sold)
1976 XS360 collector plates
1980 XS400 (on the bench)
1981 XS400 (in pieces)
2017 Husqvarna 701 enduro
Livin' the dream in western Canuckistan

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #15 on: May 31, 2016, 03:17:04 »
Put the clutch plates from an xt250 in there. A bit thinner steel plates but more of them. Nice grab and shift.

Cheers for the tip man!  Will do that.  So it goes from an 11 plate set up to 13? 7 friction plates, 6 clutch plates?

Offline cosworth

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #16 on: May 31, 2016, 03:44:04 »
Yep, I didn't count. Just know there is one more friction plate.
1981 SR250 café hot rod (sold)
1976 XS360 collector plates
1980 XS400 (on the bench)
1981 XS400 (in pieces)
2017 Husqvarna 701 enduro
Livin' the dream in western Canuckistan

Offline Ryan Stecken

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #17 on: May 31, 2016, 05:15:43 »
Very interesting.Count me in Sir!

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #18 on: Jun 01, 2016, 02:27:23 »
Day 1 of proper testing done.  I now realise how hard it will be to get any comparable results - ambient temp, weather, wind speed and riding style all play such a huge part in the running temps of the engine - obviously.  So it means that to measure and compare the effect of a performance cooling part will be pretty inaccurate.  I need to create a more controlled test environment - like scientists do haha.  For example, maybe the bike should be stationary, indoors (with exhaust extraction), fixed temp, fixed to rev at a certain rpm, with a fan blowing on it fixed at a certain setting, for a certain amount of time - then record the results.  Then repeat the tests for each different part.

Here is a photo of me trying to capture the temp displayed on this time/temp sign near where my workshop is.  Damn camera couldn't pick it up but it did say 26 degrees C.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #19 on: Jun 01, 2016, 02:41:40 »
And here are the results:

Riding on country roads with posted speed limits of 70-90kph, in 4th gear, with the engine running between 4000-7000rpm the engine had read temperatures ranging from:

Head: 165-195C
Oil-Sump: 85-95C
Oil-At Filter: 80-86C


When stopped, I quickly took temp laser gun readings of:

Exhaust Tappet Cover (side): 116C
Exhaust Tappet Cover (front): 109C
Intake Tappet Cover (front): 106C
Oil Filter Cover: 70C


And the cheapish oil filler cap gauge read 78C - which is pretty close to the temp readings at the oil filter.

Then I did two 20K (15mins roughly) there and back runs on the highway.  On the way there the bike was running between 110-115kph at 6500-7200rpm (roughly) with a head wind, on the way back with the tailwind it was running at 115-120kph at 7500-7800rpm (roughly).  When observing the gauges, the engine had read temperatures ranging from:

Head: 206-214C
Oil-Sump: 105-116C
Oil-At Filter: 92-98C


When stopped, I quickly took temp laser gun readings of:

Exhaust Tappet Cover (side): 142C
Exhaust Tappet Cover (front): 143C
Intake Tappet Cover (front): 130C
Oil Filter Cover: 81C


And the cheapish oil filler cap gauge read 95C - which is pretty close to the temp readings at the oil filter.