Engine noise under load when hot

[Pat Conlon]

Ok, gotcha...thx Noel..

[Targan]

Warning: This post is random because I don't want to start new threads and clog up the feed.

Another update: I would also like to point out that running lower on oil makes the engine hotter by far (probably common knowledge, just sharing from first-hand experience). I'm assuming it's because either 1: Low oil means less oil pressure to get oil through oil cooler, or 2: Less lubrication of engine causes more friction. Bike runs cooler now even though it's even hotter outside. Hitting 110 degrees and I sit in traffic, but no problems yet!

Also I seafoamed my bike (lazy/don't have tools/space to manually clean carbs) and just... wow. Whole new bike. It starts (stock horrible battery, slow as hell turn over cause of bigbore mind you) in 1 second every time and idles perfectly now. I never really believed in seafoam either until I tried it. I made the huge mistake of pouring it directly into the fuel line though, took me a day to get it running again lol. Trial and error.

After all my dumb trouble (half of it my fault) I have decided to permanently keep the bike, and learn to take care of it. Hopefully by fall it will be fully restored! What I need to do:
-Get undercut transmission and shift forks
-New fairings (this will be the hardest). Broken in a few places.
-CBR mirrors
-Integrated LED tail light from Randy
-New fork tubes (current ones have divets, running with zero oil)
-When fall hits tuning it for peak performance, won't have to worry about bike staying cool
-50/50 on new exhaust. Don't like the look of 4-1 or the sound of my long pipe.
-New brakes (everything from master cylinder to rotors). They're ok now, just mushy and I can tell they'll be done soon.
-Detail the bike
-Ride it until it dies because honestly I cannot find a better bike. I get all the power of a supersport with all the comfort of sport touring. And +1 for being the only guy to own one where I live (as far as I know). I love a bike with character!

[Flynt]

I'm assuming it's because either 1: Low oil means less oil pressure to get oil through oil cooler, or 2: Less lubrication of engine causes more friction.

or 3: the engine is oil cooled...  having enough oil to keep the cooling system within its design parameters is going to be critical.  Think about it...  less oil = higher temperature oil due to having less oil to absorb the engine's heat.  The higher temp actually works a bit better (dissipates more heat) in the oil cooler, but overall you get hotter oil since there is less of it.  The engine is now trying to reject its heat into hotter oil, so it will need to be hotter by about the same amount as the oil temp has gone up.

Thought of another way, the oil is another heat sink like the fins on the cylinders.  If your engine had no fins it would run MUCH hotter.  Smaller heat sinks mean less heat dissipation and a hotter engine to dissipate the same heat (this part is determined by the fuel you're burning mainly...  friction is insignificant compared to heat from combustion).  The oil system is designed to lubricate of course, but it is also a complex heat sink and needs the oil volume to make the system work correctly.

Frank

[Targan]

I'm assuming it's because either 1: Low oil means less oil pressure to get oil through oil cooler, or 2: Less lubrication of engine causes more friction.

or 3: the engine is oil cooled...  having enough oil to keep the cooling system within its design parameters is going to be critical.  Think about it...  less oil = higher temperature oil due to having less oil to absorb the engine's heat.  The higher temp actually works a bit better (dissipates more heat) in the oil cooler, but overall you get hotter oil since there is less of it.  The engine is now trying to reject its heat into hotter oil, so it will need to be hotter by about the same amount as the oil temp has gone up.

Thought of another way, the oil is another heat sink like the fins on the cylinders.  If your engine had no fins it would run MUCH hotter.  Smaller heat sinks mean less heat dissipation and a hotter engine to dissipate the same heat (this part is determined by the fuel you're burning mainly...  friction is insignificant compared to heat from combustion).  The oil system is designed to lubricate of course, but it is also a complex heat sink and needs the oil volume to make the system work correctly.

Frank

Oh wow! That makes a lot of sense. Thanks for taking the time to explain it like that! I enjoyed the read. I thought it was just because not enough oil could get through the cooler.

[ribbert]

I'm assuming it's because either 1: Low oil means less oil pressure to get oil through oil cooler, or 2: Less lubrication of engine causes more friction.

or 3: the engine is oil cooled...  having enough oil to keep the cooling system within its design parameters is going to be critical.  Think about it...  less oil = higher temperature oil due to having less oil to absorb the engine's heat.  The higher temp actually works a bit better (dissipates more heat) in the oil cooler, but overall you get hotter oil since there is less of it.  The engine is now trying to reject its heat into hotter oil, so it will need to be hotter by about the same amount as the oil temp has gone up.

Thought of another way, the oil is another heat sink like the fins on the cylinders.  If your engine had no fins it would run MUCH hotter.  Smaller heat sinks mean less heat dissipation and a hotter engine to dissipate the same heat (this part is determined by the fuel you're burning mainly...  friction is insignificant compared to heat from combustion).  The oil system is designed to lubricate of course, but it is also a complex heat sink and needs the oil volume to make the system work correctly.

Frank

Your engine turns over about one million times an hour at cruise. What makes this possible is the film of oil between the metal bits that keeps them apart, take the oil out and you would be lucky to get half way around the block before it blew up.
The clacking noise your motor makes through lack of oil is the internal bits making metal to metal contact, the oil film separating them has gone.

Oil on an air cooled bike has only a remote secondary effect on cooling. These bikes are primarily air cooled. Oil coolers are a relatively recent thing anyway, many here would have owned air cooled 4 strokes without oil coolers.
They are primarily air cooled with a radiator to keep the lubricant at a better temperature. The knock on effect does influence running temps but not a great deal. If I had to put a figure on it I would say 90% air / 10% oil.

"Oil cooling" is technically correct but mostly insignificant. Oil coolers on air cooled bikes are a relatively recent thing anyway.

Franks point about dissipating a given amount of heat into a smaller volume of oil is also technically correct but insignificant.

......friction is insignificant compared to heat from combustion). 

Frank

That's also technically true, but close running metal parts and combustion are entirely different things. The principles Frank describes would apply perfectly to a water cooled engine where that is the primary source cooling.

Where is the oil present that takes away combustion heat?

Noel

[Flynt]

Noel,

I encourage sharing some data here as you might have facts behind your assertions and maybe you can also answer the original question...  is it #1 or #2 in your view?

From distant memory I believe the heat from the engine (all sources) is dissipated roughly like this for an oil/air cooled engine:

~50% goes out the exhaust (the heating of the fuel included here),
~25% goes out the fins and other surfaces,
~25% goes out the oil cooler

The FJ lump probably has a break down that's similar, but not exactly the same.  Enough research would likely uncover a similar engine that has heat balance done to prove the percentages, but the oil is a very important part of the cooling equation and can become much more important when the fin temperature goes up...  

Combustion heats the entire engine much more than friction.  The pistons are heated directly and don't transfer much of their heat into the cyl wall (oil film insulates and slows the only significant transfer mechanism, conduction).  Not sure how the FJ engine deals with cooling pistons, but it is usually either an oil spray directed at the bottom of the pistons or just a consequence of the oil being flung around by the moving internals.  So nearly all of the combustion heat from the pistons goes into the oil, that's how.

Frank

PS - I'd bet there is some data out there in the Legends racing world to enlighten us all...?  

[Flynt]

Your engine turns over about one million times an hour at cruise.

5,000RPM (85mph cruise for me) X 60min/hr = 300,000 revolutions per hour...  FJ redline is about half a million revolutions per hour.  I'm a bit frustrated when people won't do the simple math (), but it also discredits your arguments.

Frank

[ribbert]

Sorry Frank, I did do the simple maths, at 4000rpm and meant to say a quarter of a million but I don't see it has any bearing on the point being made anyway.

The 90/10 figure I mentioned is entirely off the top of my head. I guess I view early motorbikes like the FJ as air cooled bikes with oil coolers added as opposed to engines designed around oil cooling. It wasn't long before that they didn't have oil coolers at all.
IMO "splash feed" is more about lubricating cylinder walls than drawing heat from the pistons.

I'm a bit frustrated when people won't do the simple math (), but it also discredits your argument.

Frank

I don't see the connection.

No matter, I shouldn't have bothered commenting on it anyway. It's one of those topics without a definitive answer and to no benefit.

Noel

[simi_ed]

No oil spray onto FJ pistons, so it's either fling cooling (never heard of that!) or heat transferred to the oil via contact (cylinder head perhaps?).  Where else is there a surface heated by combustion and cooled via oil contact (OK, maybe some transfer via cooling fins).

[racerrad8]

No oil spray onto FJ pistons

Sorry ed...

Incorrect, there is a oil spray hole located on the top side of the connecting rod to spray oil up onto the underside of the piston & cylinder wall.

We tried many years ago altering the hole size to increase the oil sprayed on the bottom of the piston, but with the weak oiling system of the FJ it lowers the main galley oil pressure too much, compared to any additional gain of cooling.

If we added an external oil cooler spray bar like my son's Miata has, that would help significantly.

Randy - RPM

[simi_ed]

OK, I'm starting to feel like Noel    I'm going back to my corner & observe for a while.

[Targan]

Oh my gosh you guys!  You're so civil i love it.

I am by no means a mechanic and am relatively new to motorcycles, but talking from first hand experience i know:
1. Stock oil cooler in 90 degree weather=overheating (have done this a few times) in traffic, and running hot (but fine) on the highway
2. Randy's oil cooler in 100+ degree weather=haven't overheated yet (with proper oil level) in traffic, and runs perfectly normal on the highway.
3. Less oil in my bike=overheating faster

When I say "overheat" I mean too hot to start my bike if it shuts off, it struggles to turn over (I need a new, or need to clean, starter or a lithium battery).

I'm just saying maybe just maaaaaybe oil does keep the motor cool

[Alf]

You could too replace the std plugs with 1 degree colder spark plugs. I use NGK DPR 9 EA9 (instead the 8 recommended) and it lower the temperature around 5ºC

And the Randy´s spin-on conversion get a welcome couple of degrees lower too due to the greater air flow and the extra-ammount of oil with the big filter

[Alf]

No oil spray onto FJ pistons

Sorry ed...

Incorrect, there is a oil spray hole located on the top side of the connecting rod to spray oil up onto the underside of the piston & cylinder wall.

We tried many years ago altering the hole size to increase the oil sprayed on the bottom of the piston, but with the weak oiling system of the FJ it lowers the main galley oil pressure too much, compared to any additional gain of cooling.

If we added an external oil cooler spray bar like my son's Miata has, that would help significantly.

Randy - RPM

Details, Randy, please. It looks a great mod