Loose injector adjustment

[tree98]

I watched a guy on YouTube set his 870 injectors to about half the torque they should be because he wiped out 2 cams in a row and was convinced that because his engine has over a million on it, the head must be worn in to the point that it shouldn't be set that tight. I don't agree with his theory but I am wondering what exactly happens if your injectors aren't set tight enough?

{video removed}

[Mattman]

He ran it set loose for a good amount of time. Best I recall he didn't notice any power loss running it like that.

[Volvo8873]

I have seen some of his videos. Nice guy but not sure if everything is put together in his head.

He put used cams in and on top of it. Had someone “polish” them before installation?!? That has a million miles on the motor?!?

I think he is beating a dead horse!

[tree98]

(01-12-2020 )Volvo8873 Wrote:  I have seen some of his videos. Nice guy but not sure if everything is put together in his head.

He put used cams in and on top of it. Had someone “polish” them before installation?!? That has a million miles on the motor?!?

I think he is beating a dead horse!

Yeah I cringed watching a couple of his videos, he probably just doesn't know any better and just doing what he thinks is right. Mainly it just made me wonder what is the worst thing that can happen if you leave your injectors to loose? Obviously if it's to tight it can cause excessive cam and roller wear, possibly even make the cam slip but to loose, what will that cause??

[Lonestar10]

loose maybe not get the full shot of fuel, a tiny bit of timing change, if its not touching at all with no preload maybe the taping of the rocker onto the injector could cause cracking depending on the types of metal for injector rod and rocker arm, and possibly if the rod and rocker seperate to far the rod might turn and come out from under rocker.. just some things i can think of depending on how "loose" you guys are talking i havent seen the vids.

[AussieISX]

If you run them too loose, they will not seat tight tight enough on the lower set on combustion. This allows combustion intrusion into the metering circuit in the injector. Not only will it fill with soot and block the metering check valve it will also send combustion gas through the remaining injectors in the firing order in that bank . Stupid idea in my opinion. The rocker lever is already over coming spring pressure to plunge the injector, by loosening the height setting your not relieving pressure from the cam , just ruining injectors with soot and combustion gas . I actually set mine slightly tighter than spec for the reasons I listed.

[tree98]

(01-13-2020 )AussieISX Wrote:  If you run them too loose, they will not seat tight tight enough on the lower set on combustion. This allows combustion intrusion into the metering circuit in the injector. Not only will it fill with soot and block the metering check valve it will also send combustion gas through the remaining injectors in the firing order in that bank . Stupid idea in my opinion. The rocker lever is already over coming spring pressure to plunge the injector, by loosening the height setting your not relieving pressure from the cam , just ruining injectors with soot and combustion gas . I actually set mine slightly tighter than spec for the reasons I listed.

So tightening the injectors doesn't put more pressure on the cam ? Sure seems like it would.

[Hammerhead]

(01-13-2020 )AussieISX Wrote:  ... I actually set mine slightly tighter than spec for the reasons I listed.

(01-13-2020 )tree98 Wrote:  So tightening the injectors doesn't put more pressure on the cam ? Sure seems like it would.

The injector pre-load that is set an 8Nm is the closing pressure of the pintle into the seat of the injector tip. 8Nm is not a very high torque value for a "needle & seat" as it is a tapered contact point. As long as you're only increasing it "slightly" (I don't know what value he's using, I'm just speaking in general), you wouldn't be adding a large stress to the cam/follower. An injector cam is not shaped like a valve cam. The high lobe is a larger percentage of the cam than the relief as the injector is held closed until it is "time to load" the timing and metering areas, then the cam relieves the pressure, opening the injector to be filled, then the cam drives the fuel into the charge mix for combustion...this is when the most pressure would be applied to the cam/followers as the cam/rocker/injector must produce enough physical pressure to overcome the compressed charge mixture near TDC to not only inject the fuel but also atomize it for optimal combustion, which other than during the combustion stroke is the point of peak cylinder pressure...

[tree98]

So if it's not tight enough you would get combustion gases forced into the injector like Aussieisx said?