What is a lash adjuster? - DodgeIntrepid.Net Forums - Dodge Intrepid, Concorde, 300m and Eagle Vision chat
 
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post #1 of 6 (permalink) Old 11-13-2015, 02:07 PM Thread Starter
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What is a lash adjuster?

I'm trying to research valvetrain on my 97 3.5 using Haynes manual and the web. I read plenty about lash adjusters but nothing showing exactly what they are. Can somebody describe or post a picture what lash adjusters are and how to check if they are stiff versus spongy? Thanks!
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post #2 of 6 (permalink) Old 11-13-2015, 06:37 PM
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If you know the old-school term 'valve lifters', lash adjusters are the same thing. Generally, they are what are called 'hydraulic' lash adjusters, which means they are filled with oil to give a slight cushion in the valve mechanisms, compared to similar solid metal lifters or lash adjusters called 'solid lifters'.

Hydraulic lash adjusters can be compressed by hand pressure if they 'collapse', which means they aren't holding oil due to a leak in the lifter or adjuster.
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post #3 of 6 (permalink) Old 11-13-2015, 08:41 PM
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The valve lifter/lash adjuster is a hollow cylinder with one end closed off except for a port and a check valve that only lets oil move into the cylinder, The other end has a piston in it, and the piston is pushed towards that end of the cylinder by a spring (a retainer keeps the piston from coming out of the end when the lifter/lash adjuster is not in the engine).

The lifter/lash adjuster on any engine is somewhere in line with the motion of the mechanism that pushes the valve open. As the engine runs, the lifter/lash adjuster is constantly bathed in a drip or flow of oil. If the lifter is empty of oil (full of air), there will be a gap between it and the pieces on either end, so the spring can push the piston outward. That pulls oil into the lifter/adjuster thru the check valve. Then when the gap is closed and pressure is pushed against the lifter/adjuster and the valve, the check valve is pushed closed by air and/or oil inside the lifter/adjuster. The next time the valve is closed and the gap appears, the spring pushes the piston outward again, and more oil is pulled into the lifter/adjuster. When it gets compressed again, air can leak past the piston much quicker than any oil can. This cycle is repeated until all air is out and only oil is in the lifter/adjuster.

Notice that the lifter/adjuster will only be able to fill with enough oil to keep the piston just at the point where there is very little gap, and then can fill no more. So it automatically adjusts the gap to very close to zero. Another word for 'gap' is 'lash'. Hence the name 'lash adjuster'. Also called a 'lifter' because it 'lifts' the valve open.

Below is a sketch from the FSM showing a cam lobe, rocker, and valve stem from the 3.2/3.5 engine. The '2' arrow is pointing to the lifter/lash adjuster. The arrow inside the rocker is indicating flow of oil from inside the rocker pivot rod to flood the lash adjuster.
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'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs
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post #4 of 6 (permalink) Old 11-13-2015, 10:19 PM Thread Starter
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Thanks for the detailed info! I take it the rocker assembly has to be removed to check lash adjusters? What would be reasons for needing to check them?
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post #5 of 6 (permalink) Old 11-16-2015, 06:56 AM
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There are others here more hands-on qualified than me about testing them, and I think the FSM may discuss that, and you may have come across other sources in your reading that discuss that.

Are you having problems (noise) that make you think you have lifter problems, or are you just curious about the subject? Sometimes running 8 oz. or so of Sea Foam or ATF in the engine for a few hundred miles will resolve such problems by unsticking lifter parts (check valve, piston) due to residue or grit issues - might not be advisable if the engine is heavily sludged (due to releasing too much stuff in a relatively short time). If you do that, make sure you change the filter along with the oil afterwards.


'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs
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post #6 of 6 (permalink) Old 11-16-2015, 12:29 PM Thread Starter
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Well, both. I'm always seeking to understand how things work, and I do all my own work so I like to be prepared for future projects. I do have engine noise sometimes under throttle while cruising but not from a stop. For example, when beginning climbing a hill and the engine load increases while trying to maintain speed. It sounds like clattering/tapping/ticking/knocking and goes away once the road levels. It'll begin @ lower rpm in OD then continue as it struggles to increase rpm during and after the downshift going up the hill. I've always suspected valvetrain. I bought the car 10 years ago with 72k from the original owner, like brand new, and it's always done it occasionally but I think it's becoming more pronounced. Maybe I'm just more nervous about it with the other problems I've had related to its mileage - 223k - and the work I'm currently doing on it.

You mentioned sludge...would that be visible on top of the heads? I just had the valve covers off and all looked squeaky clean with the exception of the rockers & hardware over cyl #2 which were darkened and covered in a sooty black residue, which I understand can be caused by PCV ventilation thru that area. I have another post asking about that. I'd be willing to try Sea Foam or ATF but I just changed my oil last week! Btw, I use high mileage 10w-30 (used to be exclusively Valvoline but switched to store brand -Meijer- to save $$)

Thanks again for all the helpful input!
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