Valve clearances - Too tight?

[Spetz]

Hi everyone,

I recently did the valve clearance adjustment on my Mitsubishi 6A12 MIVEC motor.

The specs are:
0.10mm intake
0.13mm exhaust

I adjusted them such that a feeler gauge 0.01mm thicker did not fit in, and a feeler gauge 0.01mm thinner fit in easily but there was still resistance.

I am not sure what the right feel is for feeler gauges so it is possible that the tolerances are 0.01mm less than factory spec.


Is this an issue? The right spec feeler gauge would slide with resistance but 0.01mm thinner would also slide with (less) resistance.

My idle doesn't drop below 1,000rpm. I checked for vacuum leaks. This might be due to the ECU relearn procedure though.

Another thing I notice is the revs drop slow after I blip the throttle. Not sure if this could be due to the valves being tight? Or it might be running lean?

 

[Chris142]

Your setting is probably closer than the factory when it left.

 

[Woofythewolf]

I would say probably fine, but if you ever find yourself running way too hot then you'll be in trouble for your camshafts and buckets/shims (some engines have shim on top as wear surface, others have shim on bottom and the bucket has a special coating- I don't know what yours is)

basically, the reason for valve clearance is that the valve stem expands as it gets hot, and you want there to be a gap for the oil film to recover even as the maximum operating temperature.

If it's too tight, then at maximum operating temperature the gap will decrease and the oil film won't be able to recover, resulting in the cam lobes scraping directly against the buckets or shims.

To really calculate if it's an issue for clearance at various temperatures I'd need the length of one of your valves, the material (probably stainless steel) and see how much expansion would occur from 70 F (temp that you set the clearances at) to say 200 F (normal operating temp to see what warm clearances are supposed to be) and then to 230 F (overheating) and see if the gap closed enough that the camshaft lobe within a few thousands of the bucket/shim.

Again, it won't be an issue unless you're running very hot (because it was designed with a safety margin so that the camshafts wouldn't be destroyed if the engine overheated-you just lost some of that margin).

Edit: the above is also true, although I would think that factory set would be on the loose side, since cam on bucket/shim tend to close up over time (I always set to the loosest spec for this reason).

 

[Silk]

It will need to relearn curb idle if you've disconnected the battery,a spin around the block should do it. Slow return to idle is an emissions thing.

 

[FCD]

My experience with setting them too tight once is that it made the engine a bit quieter, but the engine lost performance, now i run them a little loose even if they clack a bit the engine pulls great, it'll pull away in 4th ( top gear ) from 30 Km/h ( 18mph ).

 

[Trav]

Applicable only to cast iron heads, on aluminum heads valve clearance increases with higher temperature, just the opposite of iron head.
The OP's Mitsu has aluminum heads so his lash is fine, its going to increase not decrease when the engine reaches operating temp.

 

[Woofythewolf]

that's good info I hadn't thought of the heads being aluminum.

 

[Spetz]

I was always under the impression that the clearance ends up going to 0 once things expand and is there to make sure the valves completely close.
Hence why exhaust clearance is more as there is more heat and therefore more expansion.
If clearances increase then why would there be a clearance to begin with? Wouldn't this be set to 0?

So overall if I am 0.01mm too tight on the clearances would that cause an issue for me?

@Fordcapridriver,
If your clearances are too loose then you are missing out on valve lift. This might help out int he bottom end of the rpm range but is not good for overall power

 

[ZeeOSix]

Originally Posted By: Spetz
So overall if I am 0.01mm too tight on the clearances would that cause an issue for me?


That's only 0.0004 inch ... so highly doubt the engine would care.

 

[Trav]

Clearance does not go to zero. On iron heads it decreases but not to zero iron block aluminum head clearance increases all aluminum engines it increases even more. This is the reason for lower clearance values on the aluminum head engines. While hydraulic lash adjusters/lifter can be considered zero lash the preload in the adjuster/lifter acts as a soft clearance maintainer, they are not solid zero.
On new engines regardless of material clearances can close because of initial valve seat recession especially on the exhaust valves, this tends to subside after the first few adjustments.

Your particular engine (and many others) uses stellite seats which almost eliminate the recession issue along with sodium filled exhaust valve stems which further adds expansion stability of the exhaust valve stem.
There is a couple of thousands either way allowable so your fine. Do not mess around with valve clearances in order to gain lift, its a fools errand that can lead to burned valves. You want a bigger cam put one in it.

 

[Chris142]

Originally Posted By: FordCapriDriver
My experience with setting them too tight once is that it made the engine a bit quieter, but the engine lost performance, now i run them a little loose even if they clack a bit the engine pulls great, it'll pull away in 4th ( top gear ) from 30 Km/h ( 18mph ).
also lessens the valve open duration. Making more tq but less hp.

 

[Prelude]

For my car (Renault), the valve clearances are supposed to be 0.1-0.15 for the intake and 0.15-0.20 for the exhaust. When I checked them first time they all were about the same at 0.25-0.3 mm and the engine worked very well. I think at the factory they know that the specs are too tight and make all the clearances bigger: maybe 0.2 or so. I did exactly like you and made them perfect at 0.1 and 0.15. And the idle became noticeable unstable. Starting the engine took longer time. What were your clearances before you changed them? I would suggest that you change them back to what they were or closer to what they were. For the valve clearances, making them bigger by 0.05 mm or even 0.1 over the specs won't make the engine noisier. As many here mentioned that the clearances actually increase when the engine runs and may go up to 0.5-0.6 mm before you will hear any clicking.

 

[Prelude]

And yes, likely you over tightened the valves by 0.01-0.02 mm. Hold the feeler gauge with 2 fingers only like a feather and you should feel only slight resistance by your fingers. No struggling when you insert the feeler gauge.

 

[Vikas]

I have never even seen a Mitsubishi engine under valve covers but I am suspecting that your clearance numbers are wrong.
Quote:

The specs are:
0.10mm intake
0.13mm exhaust

 

[BrocLuno]

Originally Posted By: FordCapriDriver
My experience with setting them too tight once is that it made the engine a bit quieter, but the engine lost performance, now i run them a little loose even if they clack a bit the engine pulls great, it'll pull away in 4th ( top gear ) from 30 Km/h ( 18mph ).


I'm on the same team here. I run them an extra 0.01mm loose. I can usually hear a slight click, but not with the hood down. Adds much better idle and bottom end

 

[Trav]

Originally Posted By: Vikas
I have never even seen a Mitsubishi engine under valve covers but I am suspecting that your clearance numbers are wrong.
Quote:

The specs are:
0.10mm intake
0.13mm exhaust


I don't know, the US version appears to use small hydraulic adjusters similar to the ones used on some Subaru but given his location who knows what engine variant they may be using. He got the spec somewhere. If it has adjustment screws the numbers don't sound out of line.

 

[ARCOgraphite]

That sounds tight and intake only. ex is usually .2mm.

Funny, my wifes old colt SOHC 1.5L never had lash adjusted and I checked it before sale at 137K miles and the lash was all within .001" of spec.

 

[Trav]

The OP seems to be spot on for the 6A12.

Valve adjustment

 

[Spetz]

Yes most of the motors have hydraulic lash adjusters but this is a MIVEC version which revs to 8,300rpm so has solid lifters. The clearance specs are as per the engine manual.

The idle itself is not rough, and the engine starts very easily.
It just idles somewhat high however I have not driven it (just warmed it up by idling) and have always disconnected the battery afterwards so I am hoping the high idle (950-1,000rpm) will be adjusted by the ECU

 

[Vikas]

what was the clearance before you started adjusting? how much adjustment you had to do? is there any chance that mm vs inches are being confused in reading the spec?