The issue of getting, or rather not being able to get, the Old School” idling sound (Potato, Potato, etc.) from any of the fuel injected engines seems to come up fairly frequently on this forum.
Primarily this is a function of idle speed and cam timing; and I’m pretty sure that the idle speed is probably about 90% of it. My 80” 1979 Shovel Head idled at about 650-700 RPM (Great Sound). My 2010 96”is specified to idle at 950-1050 RPM. (Not as pleasing a sound).
I have the TTS Mastertune and I can put the idle RPM pretty much where I want it on my 2010 96”. I've had my 96" idling at 900 RPM for about 10,000 miles now with no issues. But that isn’t really too far off the specification either. On cars, in the late 70's and 80's they went with raised idle speeds to get a reduction in emissions, so I'm not so sure that the high idle on the fuel injected engines is all about durability.
I've read a lot on this forum about how, lowering the idle too far, can supposedly damage the rocker arms and upper valve train on a fuel injected engine. It is true that Harley cut down the oil flow to the rocker boxes on the Twinkie engines to help manage the oil temperature problems they had during the development of these engines. However, that doesn’t explain how a carbureted 88” engine can be idled down without risk of damage, but the same engine with fuel injection can’t run at the same idle RPM without being damaged. They both have the same oiling system, so the risk, or lack there of should be the same. Also, I’ve built a fair number of small block V8 engines for competition (road racing) and when I have done so, I have completely shut off the oil supply to the heads and had them idling as low as the cam will allow. While I can’t say all of these engines lasted forever (Duh!), neither have any of them had any damage to the valve train; ever Except damage such as caused by bits of connecting rods or other internal engine paraphernalia that got launched there in the last few spectacular moments of the engines life.
So anyhow, here’s my question: This business about engine damage at too low of an idle speed keeps coming up. But so do a lot of urban legends (AKA B*** S***) in the auto industry (which I am very familiar with). On this forum folks always seem to talk about low idle speed damage in the third person. In other words, it never actually happened to them. It’s always a good friend or someone that heard from someone who had a friend who sat at the right hand side of the Almighty when it came to 45 degree V-Twins, etc. . . . . I'd be curious if there's anyone on this forum who has actual first hand personal experience with having lowered a fuel injected engine idle speed to around 700 RPM and either had no problems -or- suffered some sort of negative consequences and if so, what the negative consequences actually were. .By first hand personal experience I mean that you personally own(ed) the bike when the idle speed change was made AND when any subsequent failure(s) occurred.

 

Subscribing. I doubt this is even an issue but I wonder what the oil pressure drop would be with a 200-300rpm reduction at temp in the TC vs. the predecessor engines.

For those who have done this how much more shake do you have at idle now?

 

Excellent points you have made, for sure. I don't have the answer, but I've noticed the same thing. I'll await the (first hand) judge's decision.

 

I wonder if its the cam tensioner shoes their trying to keep oiled?

 

Oil systems have to put out enough oil volume and pressure to lube the engine at low speed and high engine speed. As engine increases the oil pump out put increases. When excessive pressure develops there is an oil pressure bypass valve that will open and allow excess pressure to be eliminated by allowing so of the oil to divert back into the crankcase.

To make sure there is enough oil flow at idle the oil pump capacity will develop too much pressure at high speeds. Can't change pump capacity because the pump is driven by mechanical means.

Have seen many auto engines be idle down just to the point where any lower rpm (lower then the tune up spec) and the engine begin to miss while adjusting the carb. The oil light did not come on.

I have seen warn out engines where the oil light comes on at idle but the oil light will go out once the rpms come up. Has to because increase engine rpm increases oil pump out put.

This is how I think people assume low rpm and not enough oil flow.

Because low rpm will cause oil pressure to drop too low in a worn out engine people then make a connection that this must happen in all engines.

If we had water cooled engines we could let a fuel injection engine at a 500, 600, or 700 rpm idle and if no bearing or any other parts don't start making noise due to oil starvation and or the engine does not seize then it would be safe to assume that the faster idle rpm's is an emission driven specification.

Those that ever had to do emission's testing on a car back in the 80's do you rememeber what was done when a car just was failing the emissions test?

The mechanic would grab the trottle linkage and increase the rpms about 200 more and the engine then would run clean enough to pass.

Took awhile for the gov to get smart and use PC controlled testing systems so mechanics could no longer do this.

 

With plain bearing engines like Chevy small and big blocks the oil warning light (idiot light) was set to come on at 5 psi. On high mileage V8s I have seen the light go on and off when warm sitting at stoplights with no negative consequence to the engine. The twin cam engine with roller crank and rod bearings should not be as susceptible to damage from low oil pressure as long as there is some oil flowing to equalize the heat. Good data would be from mounting up an oil pressure gauge and seeing what a stock twin cam oil pump is producing at the factory 1100 rpms and stepping it down 1000, 900, 800 etc.

 

My '99 RK TC88 idles at around 700-800 RPM. Has been that way for over a year now. Rarely does it idle above 900. Once in a while, it drops to almost 400rpm, guessin that's from the MM ignition? Don't have an oil guage installed, but I did install a Baisley (LMR-004) spring when I went through the valve train. I've had no indication of oil related problems, so far... and I've put almost 10K miles on it since that install.

 

[quote=Just Enough;7621811]With plain bearing engines like Chevy small and big blocks the oil warning light (idiot light) was set to come on at 5 psi. On high mileage V8s I have seen the light go on and off when warm sitting at stoplights with no negative consequence to the engine. The twin cam engine with roller crank and rod bearings should not be as susceptible to damage from low oil pressure as long as there is some oil flowing to equalize the heat. Good data would be from mounting up an oil pressure gauge and seeing what a stock twin cam oil pump is producing at the factory 1100 rpms and stepping it down 1000, 900, 800 etc.[/quote

Also to add to this that at idle the parts are just floating because they have no load placed on them with the transmission in neutral.

 

Ive got my '07 96" idling at 900 too with the TTS. Same thing, about 10k miles and Ive had no issues. Ive also been told there isnt a difference between my fi twin cam and a carb twin cam. When I get through with some other mods and have to tune again, Im going to toy with an 800 rpm idle.

 

Subscribing. I'd like to lower my idle as well, but good sound is not worth engine damage. This will be good. I'll wait here...