Straight weight in a bike?

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Chris142

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I bought a dirt bike that uses the engine oil to lube both the engine and the trans. Since the transmissions in these tend to eat the multi viscosity oil up fast would a straight 30 or 40 be a better choice?

I'm not concerned about cold starting. If it's not 90F+ I'm not riding.
 
I had good results with 15W-40 HDEOs in street bikes.

Go for the Allison C4 spec on the 15W-40 while you're at it.
 
A multi has the "potential" of staying thicker as it heats up past the 100c temp rating (30,40,50 etc), bikes often can exceed 100c. Just something to consider not a rule.
Many times viscosity index improver's in multis are criticized in bike oil discussions but they fail to mention there may be a positive benefit? How long this benefit lasts in the life of the oil is debatable, but the debate usually ends with cause for reasonable short oil changes whichever oil you choose.
 
Some dirt bikes are harder on the fluids than others.
KTM's, using roller lifters recommend up to 15 hours of run time for their 4T bikes OCI.

Yamaha YZF's will probably need a change quicker than that with the plain bearings and solid lifters.

I never go more than 4-6 hours of run time on any dirt bike fluid, 2 stroke or 4.

A top shelf 40wt. will be a fine choice for any dirt bike engine.
I would personally go with Rotella T, Delvac 1300, or Delo 400 15w-40. The proven performance and bargain pricing makes these HDEO's hard to beat.
 
Quote:

A multi has the "potential" of staying thicker as it heats up past the 100c temp rating (30,40,50 etc), bikes often can exceed 100c. Just something to consider not a rule.
Many times viscosity index improver's in multis are criticized in bike oil discussions but they fail to mention there may be a positive benefit? How long this benefit lasts in the life of the oil is debatable, but the debate usually ends with cause for reasonable short oil changes whichever oil you choose.

Click to expand...
A straight viscosity oil will have a stronger film strength in high sheer areas of the engine as there are no viscosity improvers to shear.
 
Quote:

I bought a dirt bike that uses the engine oil to lube both the engine and the trans. Since the transmissions in these tend to eat the multi viscosity oil up fast would a straight 30 or 40 be a better choice?

I'm not concerned about cold starting. If it's not 90F+ I'm not riding.

Click to expand...
Use some of the 15w/40 you have. Chris ,,,again how are you going to save up for a house?
 
try the 15w40 and forget about it. its designed for wet clutch use. its made incredibly robust for diesel engines. and although you only use the bike in hot climate, the 15w40 will be thinner for startup than a straight 40. last thing is that youre changing the oil every 15 hours or less, youre not going to shear an oil in that short of time. youll probably dillute it with fuel. but shear it badly? nahhh

but a gallon of 15w40 and change it often. youre engine probably doesnt even have a oil filter. but you have a wet clutch and a shared engine and trans. the oil gets contaminated quickly via clutch particles. 15w40 is cheap compared to $88 /qt bike oils so change the oil often and dont worry.

did i meantion to change it often?
 
There was a member in your area who used straight weight 40 or 50 oil in his street bike. He kept a light bulb under the engine to keep the oil warm.

I gave up trying to find the thread.
 
The bike I bought is known to have camshaft problems. The exhaust cam lives in a bucket of oil but the intake cam is out in the wind.

Same basic engine my quad had and Amsoil, Motule 10w-40 synthetics didn't do any better than the cheap dino oils.

I was just thinking outside the box wondering if a straight weight would be a better chioce.

Master Acid: I does have a oil filter. Quite big for the size of the bike.
 
Another thing to consider...
While a st wt oil may not have the VIs that can be sheared down easy, they also will lack the detergent/dispersant package of a multi-grade. Especially that of an HDEO.

When using a fluid to lubricate a clutch pack, there are loads of particulates that come off immediately and often.
I like using HDEO in such an engine, as it is better at cleaning and keeping the particulate suspended until OCI, which should always be a short one for a wet-clutch situation.
 
Quote:

There was a member in your area who used straight weight 40 or 50 oil in his street bike. He kept a light bulb under the engine to keep the oil warm.

I gave up trying to find the thread.

Click to expand...


That was/is me. Intruder 1400. 5000 mile oil change intervals. Oil's almost as clean when I drain it as when I first put it in. I'm easy on it though as the bike always goes a minimum of 120 miles for every cold start.

I just commented to him in a different thread regarding the use of a mono-grade. No riding under 90F+, I'd be using SAE-50, not SAE-40.
 
I have used the bel ray thumper oil and it is 20W50, the rotella is certainly cheaper and performs good. I have run the rotella in my crf250 and my ninja zx9r with no problems.
 
Quote:



I never go more than 4-6 hours of run time on any dirt bike fluid, 2 stroke or 4.


Click to expand...

laugh.gif
 
Do you're own experiments and get the oil analyzed. Consider the money spent as educational, but also get the analysis done by Dyson. You might also have fuel dilution when chemical shearing and other considerations beyond physical shearing. You oci might also be driven by particle contamination.
 
Originally Posted By: Gary in Sandy Eggo
Quote:
There was a member in your area who used straight weight 40 or 50 oil in his street bike. He kept a light bulb under the engine to keep the oil warm.


That was/is me. Intruder 1400. 5000 mile oil change intervals. Oil's almost as clean when I drain it as when I first put it in. I'm easy on it though as the bike always goes a minimum of 120 miles for every cold start.

I just commented to him in a different thread regarding the use of a mono-grade. No riding under 90F+, I'd be using SAE-50, not SAE-40.

I forgot to add that my 5-quart capacity bike uses about 1/8" of oil on the dipstick (less than 1/4 of a quart) between 5000 mile oil changes.
 
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