Valve adjustment - problem

[boost]

Hi guys,

 

Tried to adjust the valves on the L26.

All of the valves were off. Managed to adjust all except the number 4 and 6 intake valves. I have run out of adjustment. I have unwound the adjustment nut as far down as possible yet the clearance is still not within spec.

Am I doing something wrong ? Shouldn't there be ample adjustment both ways.

 

Loosen the jam nut and lower/raise the adjustment nut as required..

[pauly_adams]

you prob have worn out rockers, so you will rather need new rocker arms or buy some thicker lash pads

[Enzo]

Hi,

    " I have unwound the adjustment nut as far down as possible yet the clearance is still not within spec."

The adjuster needs to be wound up not down. Wind up to push the rocker arm closer to the camshaft. Use a feeler gauge between the rocker and the cam lobe. Hot adjustment inlet 0.25mm- exhaust 0.30mm.

Cold adjustment inlet 0.20mm- exhaust 0.25mm.

 

[1600dave]

So, they are still too tight ? (ie you need to get more clearance, but can't because you can't wind the rocker pivot down far enough ?

 

Have you checked the wipe pattern on the rocker ? Does it still have the standard cam ?

 

You may need thinner lash pads (the little "buttons" on top of the valves that the rocker pushes down on).

[Riceburner]

Are you turning the motor over as you do them? They should be measured on the heel of the camshaft for each rocker.

[boost]

Enzo - it's definitely wound down not up. Wounding it up with reduce the clearance. I need more clearance.

 

Dave - No I haven't checked the wipe pattern. This is the first time I've heard of this term. I'm pretty new to valve adjustment. What does the standard cam look like ?

 

Gareth - Yes I am turning the motor so that each lobe is pointing upwards and I'm measuring with feeler gauges at the heel.

 

 

 

[dat2kman]

Lower adjuster posts right ff, remove the offending rockers, and post up pics of the lbe wipe surface.

If it is a bit wavy/undulating, they are stuffed, and will need a reface grind, to get them back to correct curved shape.

 

Oh and put in some high ZDDP based oil additive concentrate.

The lack of zinc in mdern oils causes more wear on metal/maetal wipe areas than ouls f old.

[boost]

The adjuster post is lowered as far as possible. How do you remove the rocker ?

 

A pic of the cover off

 

cylinder #4 lobes

 

cylinder #6 lobes

 

Do the lobes look ok ?

 

 

 

[1600dave]

Okey dokey - first question, what clearance can you get with the adjusters wound right down ?

 

What is the history of the engine ? Any chance it has had a different cam put in it ?

 

Have the valves been replaced ? What state are the valve seats in (ie are they badly "pocketed" or sunken ) ? Not something you can tell from the outside unfortunately.

 

I'm trying to work out how you have got into this situation. L-series valve setup is a bit misunderstood at times, perhaps someone lacking the understanding has messed about with it previously ?

 

Normally, to remove the rocker arm, you would wind the adjusters right down to get some wiggle-room and slip the rocker arm out. If you don't have enough clearance, you may have to compress the valve springs a little to get the arm out.

 

Here's a quick "L-series rocker arm setup 101" lifted from another post I did a while back. You will have the opposite "bad" setup to what I drew up back then, with the pivot side of the rocker arm right down and the valve side right up.

 

If you can get your head around how it works, you can probably see that to get the geometry correct (ie get the rocker wound up more) , you need to get different thickness "las pads" - the little buttons on top of the valves. In your case, you will need thinner ones. Whether you can get them thin enough will depend on why your setup is how it is. I'll see if I can find a post on how to check the wipe pattern on the rocker arm wiping surface (the bit that the cam runs on)

 

Quote from older post below vvvvvvv

 

And here we go, before and after fitting a reground cam.

 

In the top sketch (original cam), the cam lobe wipes across the inserted pad on the rocker evenly.

 

In the second sketch (reground cam), the base circle has been reduced in diameter. Therefore there is a gap between the rocker arm and the cam (gap is the amount the cam has been "ground" down) - therefore massive valve clearance.

 

No worries, lets just wind the rocker arm pivot right up, same way you would adjust valve clearance normally, except much more.

 

You end up with something like the sketch, rocker pivot needs to be wound up roughly double the difference (because the valve spring end of the rocker can't change position).  The inserted pad is now pulled a little towards the pivot side due to the angle of the rocker. I should have actually shown that the rocker tip on the valve is also moved towards the rocker pivot. Imagine if you like a ladder - you change the angle of the ladder, and the feet of the ladder move towards or away from the wall.

 

So, the correct way is to increase both the height of the rocker pivot AND the other end of the rocker by using a thicker lash pad.

 

the problem of having the inserted rocker pad not central is that the cam can run off the end of the pad and onto the rocker arm itself. See pic for what this does to the rocker (this was the last engine I built when I pulled it down - previous owner hadn't got the geometry right and destroyed the rocker arm and the cam itself. You can see the black-ish section on the left hand quarter of the pad where the cam hadn't been wiping and the wear concentrated on the opposite end.

 

Sorry to ramble a little, but the first few engines I built years ago I didn't pay attention to this stuff, resulting in a few issues. Its not intuitive and can be hard to get your head around.

 

 

 

 

[1600dave]

Thought I'd posted it before, here is setting up the correct "wipe pattern" on the rocker arms. You may notice that I'm only using a single valve spring in the pics, its way easier to set this stuff up with the head on the workbench, but it can be done on the car vvvvvv

 

 

 

Need to check the rocker wipe patterns since I've put a new cam in it. Bit of texta on the rocker face

 

 

 

Set it up and turn the cam to wipe the texta off again.

 

 

 

That's what we want to see - first valve is pretty much spot on  :thumbsup:

 

 

 

Next one isn't though 

 

 

 

Plenty of mucking about with various combinations of bits of chopped up feeler gauges between the lash pad and rocker arm, trying and re-trying till its good. Then repeat fot the rest of the valves  :roll: . There's a good few hours work just in getting this right.

 

[boost]

Thanks for the reply Dave. To answer your questions.

 

" what clearance can you get with the adjusters wound right down ? " -  I'll have to put the feeler gauges on and get back to you.

 

"What is the history of the engine ? " - No idea. I bought it off the 2nd owner and never asked him about the engine. It did come with 240z round top hitachi's so there was some fiddling around.

 

"Any chance it has had a different cam put in it ? " - No idea. What does the OEM cam look like ? Can you visually tell just by looking at it?

 

"Have the valves been replaced ? " - once again no idea. The owner I bought it off never mentioned anything about engine work being done.

 

I'll have to remove the rockers, texta it and reinstall to see what the wipe pattern is like.

 

Also I noticed in your last pic you inserted the feeler gauge on the valve side not the adjusting nut side. Is there any difference which side you insert the gauge from ?

 

Do the lash pad's simply pop off or are they screwed in ? If all I need is thinner lash pad I could mill off some material at work.

 

 

[RLY240]

As above there is something amiss with the geometry as you should be able to lower the adjusters enough to wiggle the rockers out.  If you bottom out the adjusters and still have zero clearance then there is a problem and the only way to remove the rocker is to compress the valve spring (mind your fingers).

The questions then is how did this evolve.  It doesn't take much to alter the geometry so I'm guessing that either the valves have recessed into the seats over time, or someone has installed longer valves (or cut new seats that sit deeper into the chamber) or the top surface of the head has been skimmed to correct a slight warp as this then sits the cam towers lower. Or simply fitted lash pads that are too thick.

 

Once you work out what has occurred you can get the clearance you need with a combination of shims under the cam towers and lash pads sized to give you the correct wipe pattern as described earlier. Or thinner lock nuts on the adjusters if you're desperate or a reground camshaft with a smaller base circle and higher lift....

Curious to know what size lash pads are in there.

Roger

 

 

[PeterAllen]

Dave. Congratulation on your post re Texta, etc. That attention to detail and technique brought a smile to the face of an old aircraft engineer. It's good to know those skills are still about.

[Linton]

picture 3 the valve spring doesn't look right on the bottom where it sits on the washer, could you have a broken valve that will give you zero clearance. a photo the other side would be good

[44014]

Is it just me or do those valve lash caps look wayyyy oversize for a standard unground cam?

Have you measured the lash caps?

[1600dave]

It doesn't matter which side you stick the feeler gauge in from.

 

Lash pads just sit loosely in the valve cap. You just lift them out with your fingers.

 

Milling them down will probably help, personally I'd still like to know why they are like that. Most of these points have been mentioned earlier, but for some reason, the top of the valve looks to be to high up (valve head is "pocketed" in the head, valve seats are worn or badly reconditioned), valve is too long (some L28 valves are slightly longer), lash pads are too thick (effectively adding length to the valve) or the cam is too low in the head (top of head has been milled for some reason, effectively bringing the cam down towards the rocker pivot and valve).

 

Wipe pattern will tell you a lot.

[Enzo]

Quick question. Are you setting the cam on the rock with the inlet and exhaust lobes for the valves you are adjusting pointing both up. When these are adjusted rotate the cam to adjust the next two in the sequence. Firing order 153624.

[Linton]

so long as it points up it doesnt matter, the gap is the same at least that has been my understanding for the last 40 odd years since doing my apprenticeship on these things.

[boost]

I'll have to take the rockers out and do a wipe pattern check. I'll also measure the lash pad thickness and report back.

 

I measured the gaps with the lobe pointing up.

[Riceburner]

Do the lash caps on inlet 4&6 look the same height above the spring retainers as the others?

 

If it's a refreshed head/engine that hasn't run or been tested perhaps he installed a couple of mismatched lash caps mixed up during the rebuild?

[Zedman240®]

Is it just me or do the lock nuts on the rocker arm pivots look a bit thicker than the other ones? Maybe someone re built the head and used nuts from another model head?

[boost]

Zedman - I had a closer look. They look to be all the same height.

 

Gareth - Just looking at them in situ they seem to be the same height but I guess they need to come out and measured with a micrometer or at the very least verniers.

 

This is how they look.

 

cyl #6

 

 

cyl #4

 

Does anything look obviously wrong from this angle of the engine ? How can you tell if it's a stock cam or aftermarket ?

 

[RLY240]

From what you can see in the pics the wipe pattern doesn't look too bad, at least the cam is still on the pad and you can just make out the marks. I'm still guessing either recessed valve seats or a skimmed top surface but either way you should be able to measure up the required lash pad thickness as described earlier and buy some thinner new ones.

Hard to pick a factory cam from aftermarket, most are regrinds anyway in which case the base circle is smaller meaning you should have more clearance not less, hence using a regrind cam (for more lift) would give you back some clearance on the adjusters.

Roger

 

 

[boost]

Tried to remove the rocker arm to texta the wipe surface and see what the wipe pattern is but I can't remove the arm. I was under the impression that once the rocker arm retaining spring is removed the arm should be pretty easy to remove. Not so in my case. The valve spring seems to be pushing against the arm. What's the best method to compress the spring ?

[Linton]

make sure the lobes are facing up and lever the valve spring down with a pry bar or heavy screw driver just enough to slide the rocker off the post