Lash Adjusters - Bleeding to Solid

[brw0513]

Hello All.

I'm really enjoying working on my 6G74 engine

I've been doing some research before removing and inspecting my lash adjusters. The Mitsubishi service advice states to fully expel any air in the lash adjuster in a bath of diesel. The process doesn't seem hard, but I'm wondering why the lash adjuster gets installed at its full height.

Would I be right to assume the intended function of a lash adjuster is to maintain the optimum dimension (i.e. height) between rocker and valve stem tip over the life of the engine?

If so, I don't really understand why a new lash adjuster would be installed at its maximum "fully bled" height. For a particular valve couldn't this mean it doesn't seat fully prior to the piston reaching TDC?

Why doesn't it go in part bled and be given a chance to attain its perfect height?

Or is the diesel some magic brew for the lash adjuster that is easy enough to expel then get replenished to the required height with engine oil?

Thanks.

[disco stu]

While this post hasn't attracted any attention, I don't want to double post about the same issue. I've been wondering why you want it at full height as well.

To add to this.....My engine looked like it hadn't had any oil changes done for a fair while before I got it. Oil was very dark, and it was run on lpg, indicating very old, plus engine had sat for for 2yrs. Engine running it is fairly noisy in the top end with general tappet noise I'm guessing. I decided to flush oil system out with eventually about 3/5 diesel and 2/5 oil. I expected the engine to get noisier and to get a lot of tappet noise while this mix was running in it, but it was the other way around-it got really quiet and seemed to be better.

I drained it for a full day to try and get as much of the diesel out as possible, and now running 10w40 oil in it its back to tapping away same as before. I'm in the process of pulling the top down for rocker covers, spark plugs, timing belt etc

Can anyone explain why it quietened up with the much thinner oil?

Anything I can do with the lash adjusters while I've got the rocker covers off to try and get things running right there?

[erad]

The lifters are designed to maintain a constant (minimal) clearance. When the engine is not running, there will be some of the valves which are left in the partially open position. Once the engine is started these valve lifters have too much clearance and they will clatter. They will be refilled with fresh oil and oil will seep out of these lifters. If you have oil (sticky, gunky) oil, it will take a lot longer to refill the lifters, hence they will be noisier than those with fresh oil. When the lifters becomes worn, they lose their oil too quickly and hence they tend to be noisier than good ones.

[disco stu]

Cheers Erad. But why would they run so quietly with diesel for lubrication? Pressure would have to be lower in lubrication system running much thinner lubricant, and the expectation was for it to be very noisy. I'm wondering if its an indication that the oil pump is getting overly worn and can't pump up to pressure with the higher viscosity oil

[old Jack]

Lash adjusters are also known as hydraulic lifters and their purpose is to maintain zero clearance of the rockers to the camshaft and the valves. Before reinstalling hydraulic lifters they need to be " cleaned and bled", this process means you wash out all the oil from inside and then collapse the lifter to its minimum height on installation and set up the correct valve/tappet clearances. When the engine is first started up the oil pressure pumps up the lifters to obtain a zero tolerance. Hydraulic lifters should be a set and forget for the life of the engine or until they are removed or you get a "sticky lifter".


OJ.

[disco stu]

Thanks OJ. Any idea why the very low viscosity oil causes them to be quiet while the higher/normal viscosity causes them to be noisy/not expand out properly?

I'm trying to work out if I need to do something while I'm in there doing timing belt and got rocker covers off

[erad]

Thinner oil (with or without diesel added) will allow the lash adjusters to get to their set length quicker than with heavy oil. Heavier oil will take longer to get into the lifter, I don't think that they are refilled in service by pressure oil - I think they get filled from a mini sump on each lifter getting filled with oil splashed around from the rockers. Again, heavier oil will take longer to get into the lifter.

[old Jack]

Thinner oil (with or without diesel added) will allow the lash adjusters to get to their set length quicker than with heavy oil. Heavier oil will take longer to get into the lifter, I don't think that they are refilled in service by pressure oil - I think they get filled from a mini sump on each lifter getting filled with oil splashed around from the rockers. Again, heavier oil will take longer to get into the lifter.

Here is an explanation on how hydraulic lifters get the oil.

Basically a hydraulic lifter has a built in oil pump with a one way check valve to prevent it from collapsing.

https://www.youtube.com/watch?v=lorANZ1Tptw

OJ.

[disco stu]

That is interesting, thanks guys. I always thought it was just main pressure that pumped them up, but that changes things. I just read about the rev process for getting them sorted out, I'll try that once the engine is back together. Didn't want to find out I had to pull everything off again once I had finished

[erad]

When my 3.5 L engine was reassembled, it rattled like a machine gun, but after a few minutes of idling the mechanic friend then revved the engine a bit and it all went delightfully quiet, so revving the engine does work.

[disco stu]

I'm surprised how exact the process is described in the workshop manual. For the benefit of anyone who reads this later on, as described for a 6g74 engine in an NL: take 15 sec to increase revs from idle up to 3000 (reaching 3000 at 15sec), then immediately drop revs back to idle and leave it there for 15s. That is one cycle, and repeat for up to 15 cycles (I think, from memory)

[gork]

So what's the verdict? Should the lifters be installed at full height? The replacement ones I've just received are fully extended. I suppose they'll 'leak down' to an appropriate height but I don't want to cause any issues, and I assume reassembly may be harder too.

[old Jack]

So what's the verdict? Should the lifters be installed at full height? The replacement ones I've just received are fully extended. I suppose they'll 'leak down' to an appropriate height but I don't want to cause any issues, and I assume reassembly may be harder too.

Hydraulic Lifters should be fully compressed/collapsed when installed and the correct valve clearances setup on the rockers. Once the engine is rotating then they will "pump" themselves up. A method we used after overhaul piston aircraft engines was to have the spark plus removed and the fuel and ignition systems disabled, then crank the engine over using the starter and several batteries for several minutes.


OJ.

[disco stu]

There isn't any way to adjust I thought Old Jack-only the hydraulic lifters themselves?

What Old Jack said seems logical to me and most on here it seems, but is in contrast to what the manual says where they say to pump them up to full height before installation. I might give that trick a go with my engine.

Installation wouldn't be any harder or easier. Just put it all together and slowly bolt down evenly, some will be pressing on cam lobes

[old Jack]

There isn't any way to adjust I thought Old Jack-only the hydraulic lifters themselves?

What Old Jack said seems logical to me and most on here it seems, but is in contrast to what the manual says where they say to pump them up to full height before installation. I might give that trick a go with my engine.

Installation wouldn't be any harder or easier. Just put it all together and slowly bolt down evenly, some will be pressing on cam lobes

Ok, I have read the workshop manual for a 6G7 series engine fitted to 2007 Pajero, and it appears Mitsubishi use a "preload method" of adjustment. This is detailed in the rocker and camshaft installation procedure in the engine overhaul section of the service manual and this should be read and understood fully, it is not particularly clear and it took a while for me to get my head around this procedure.

The Service Manual also indicates that auto lash adjusters (hydraulic lifters) are only fitted to the exhaust valves and there are solid lifters used on the intake valves! So the intake valves need to be adjusted by the conventional method.

1. There is a very specific procedure for filling the lash adjusters/lifters with clean diesel, this eliminates all the air from inside the lifter and then the lifter is installed in the fully extended position which is contrary to other engines I have worked on that have hydraulic lifters. It is important that no diesel is allowed to drain out of the lifters after filling and before installation.
2. Prior to installation the service manual directs you to adjust all the rocker adjusting screws to 3mm protrusion, temporally. After this the directions are vague at best, but my understanding is the rockers and rocker shaft assembly is then installed and tightened down. This will partially compress the lifters that are on any part of the camshaft. What is not clear is if this is the final procedure and if further adjustment is required of the rocker adjustment screws or even to tighten them.

Whilst I do not like this particular method of installation, it is what the manufacturer recommends so in absence of an alternative procedure then it should be followed.

On other engines I have worked on the lifter is fully collapsed and full of oil then the rocker adjustment screws are set to a specific clearance when the piston is at TDC and the cam lobes are in the lowest position. The procedure is then repeated for each cylinder.

OJ.

Forgot to post that lifters and camshaft should be renewed altogether, if you are reusing camshaft and lifters it is important that the lifter is installed in the same valve and cylinder position as they will have "worn" to mate together.