Valve settings for Perkins 4.108

[pr2501]

Manual says 0,30 mm for Intake and Exhaust

On internet the data is Exhaust 0.30 mm cold.

Mechanic was saying Exhaust 0.40 and intake 0.35.

Is it that is he mistaking or is that is better practice to open valves more?

[a64pilot]

Go with what the book says, cause well you know, it’s the book

However valves wear and tighten up, not loosen as many think, and the exhaust valve does get hotter and therefore the clearance does tighten up when hot, so your mechanic seems to know what he is talking about and may have considerable experience.
The slight bit of loosening he is talking about isn’t enough to hurt anything in my opinion, and is well within what I consider tolerance.
There is always a tolerance of course, even when none is stated.

He is likely thinking a new engine where the valves wear a Little initially, or set them loose to extend checking intervals, because most people never adjust their valves

[DougR]

I suggest you follow the information in the manual.

If you set the valves with a larger gap, they will open less than specified, but the difference probably won't be significant in terms of engine performance.

What will happen is that the tappets and rocker arms will be noisier than usual. Also the tappets and camshaft could experience accelerated wear because they are missing some of the opening and closing ramps on the cam lobe. Not an immediate problem, but long term longevity will suffer.

DougR

[pr2501]

Thank you.

[Bill O]

Here a hot rod article on how they do valve lash settings and why it's important. Agree w/the article to keep the gap smaller to avoid wear than larger as suggested by the mechanic.

Other nuggets that I was reminded of in the article (been a while since I've been really working on car motors while growing up in Detroit).
1. Do the setting on a cold motor.
2. First set all intakes, then set the exhaust.
3. To make life easier, adjust valves (intake then exhaust) following the firing order which involves less turning of the motor by hand.

Setting the valve lash is just as important for any motor and is something that is often over looked for for a simple maintenance task.

[Lepke]

In aircraft piston and racing engines, when trying to determine if a cam grind change will give more hp or economy, etc., it is common when on a dyno to adjust the valves tighter and looser for different runs. Leaving the valves loose or tight will shorten engine life and could lead to catastrophic failure.
Engine manufacturers go to great lengths to determine correct valve settings. After all, they usually come with a guarantee. Most settings are cold. If you want to know hot, after a run where the engine is fully warmed and coming off near full hp, check the lash.
There are tools that will measure lash and adjust the setting while running. Not cheap.