Sea Water and Oil - How Much is Too Much for an Engine (2QM20)!

[JPA Cate]

Wottie,

The spring you showed us had rust on the end, where the material is flattened. Maybe you could photograph that, too, for comment.

Ann

(Yes, still following...)

[Compass790]

Ignore my post #59 Wottie as i had another look in better light at your "flame nozzle" & it looks perfect. Might have been beer goggle distortion on first viewing.

v/v springs don't look bad to me but I've never had rusty valve springs in an engine so that means nothing. Professional engine reconditioners advice needed on that one

Collets & spring cups I can't see being an issue

[GILow]

I’ve forgotten... what am I following?

[PaulMarion]

Great result so far Wotname. Spring "tension" is what's needed. Normally checked with a compress tool with gauge attached, however as long as they're pretty uniform they should be okay for the lower revving diesel motors. If one or more springs are really easy to compress, (by hand) valve bounce will happen. I've actually had a couple of motors that have run poorly at idle, although compression readings were good via stater motor speed. After chasing other causes without success, I removed the rocker cover and individually pushed each valve down manually, and found a weak spring. It was valve bouncing at idle!

[PaulMarion]

The other item I would check are the valve "end caps" in figures 5 & 6. I noticed they "appear" to have wear and pitting on their tops, where the rockers push. If so you will get false tappet adjustment readings. Make sure they are flat and square on their tops, and also check the rockers to make sure they also don't have a worn indent. Both can be ground square again by using a fine stoned bench grinder, or if you watch your fingers carefully, a fine stoned angle grinder. Be careful as the valve caps are very slippery critters using either method!

Hope this is useful.

[Wotname]

Originally Posted by JPA Cate

Wottie,

The spring you showed us had rust on the end, where the material is flattened. Maybe you could photograph that, too, for comment.

Ann

(Yes, still following...)

Here you go!

I had difficulty getting it in focus - mainly due to my poor camera skills and an ageing iPhone camera.

[Wotname]

Originally Posted by PaulMarion

The other item I would check are the valve "end caps" in figures 5 & 6. I noticed they "appear" to have wear and pitting on their tops, where the rockers push. If so you will get false tappet adjustment readings. Make sure they are flat and square on their tops, and also check the rockers to make sure they also don't have a worn indent. Both can be ground square again by using a fine stoned bench grinder, or if you watch your fingers carefully, a fine stoned angle grinder. Be careful as the valve caps are very slippery critters using either method!

Hope this is useful.

Yes, you comments are helpful - thank you.

And yes, some of end caps are pitted, especially the circled red ones. I assume these are surface hardened so I wasn't sure what was the best approach. Leave it and keep an eye on the tappet adjustment. Try to grind it back somewhat and then keep an eye on the tappet adjustment. Get new (or good used ones). I guess the best approach is to replace if possible but.....

To grind them, I would probably make up an hardwood "jig" to hold them and use a fine belt on the linishing tool. Is there any worthwhile DIY method of rehardening the surface post grinding??? We used to harden mild steel with heat and oil quenching but I dunno if that it good enough for these items or if I would simply be making matters worse!

[Wotname]

Originally Posted by PaulMarion

Great result so far Wotname. Spring "tension" is what's needed. Normally checked with a compress tool with gauge attached, however as long as they're pretty uniform they should be okay for the lower revving diesel motors. If one or more springs are really easy to compress, (by hand) valve bounce will happen. I've actually had a couple of motors that have run poorly at idle, although compression readings were good via stater motor speed. After chasing other causes without success, I removed the rocker cover and individually pushed each valve down manually, and found a weak spring. It was valve bouncing at idle!

The manual does give a loaded spring force but I haven't checked it yet. It also gives free length of 38mm with a wear limit of 37.7mm These springs measure at 37.4mm.

Sort of thinking now they should be replaced considering the rust and length but always open to other ideas.

[jimbunyard]

I'd ask your head guy what he thinks.

From the pictures, what concerns I would have would be with the pits on the springs shown in the 2 enlargements below.

I'd have no problem using any of the other parts, though the clean-up procedure on the caps and rocker arm contacts Paul recommended seems like a good idea to me. Also another good place to get the head man's opinion; he may even have a grinder specifically for that job.

For my personal use, and this is not a recommendation, unless the parts were readily available and reasonably priced, I'd probably run what I had. That is unless the part's condition are actually worse than can be seen in the pictures.

The orange is more concerning, the yellow less so. What looks like deep pits shown in the second picture are most concerning, because the corrosion could be more extensive than shown on the surface.

[PaulMarion]

I'd be replacing the springs after comparing the results to the specs. Not worth the chance of dropping a valve because of their weakness or breakage. Regards, Paul.

[a64pilot]

I believe spring height is used as a way to determine fatigue, eventually all springs if cycled enough will break, so I’d replace them.
Having said that, it’s very common on overhauls to shim the springs, and they get away with it too, so who knows.

[jimbunyard]

Didn't notice the measurement post. Nonetheless, the difference in go/no-go is .3 mm, or .011", the difference in standard length and observed length is .6 mm, or .023".

In my mind, the critical criteria are the extent of the pitting and the measurement of length at load (if you're lucky the book will list two values); neither criteria lend themselves very well to an online evaluation.

[Wotname]

Originally Posted by a64pilot

I believe spring height is used as a way to determine fatigue, eventually all springs if cycled enough will break, so I’d replace them.
Having said that, it’s very common on overhauls to shim the springs, and they get away with it too, so who knows.

Originally Posted by jimbunyard

Didn't notice the measurement post. Nonetheless, the difference in go/no-go is .3 mm, or .011", the difference in standard length and observed length is .6 mm, or .023".

In my mind, the critical criteria are the extent of the pitting and the measurement of length at load (if you're lucky the book will list two values); neither criteria lend themselves very well to an online evaluation.

Regarding free spring height, I can't help wondering if there is a mis-print in the manual I am using. Out of curiosity, I checked three other small Yanmar engines, 2QM15, 2GM20 and YSM12 manuals. These engines have a max rpm between 3000 and 3600 while the 2QM20 max rpm is 2800.

2QM15: free height 36.5mm, wear limit 35mm (difference 1.5mm)
2GM20: free height 38.5mm, wear limit 37mm (difference 1.5mm)
YSM12: free height 40mm, wear limit 38.5mm (difference 1.5mm)

This pattern is quite different to the 2QM20 manual which is free height 38mm, wear limit 37.7mm (difference 0.3mm).

It doesn't feel correct...

[Compass790]

Originally Posted by Wotname

Regarding free spring height, I can't help wondering if there is a mis-print in the manual I am using. Out of curiosity, I checked three other small Yanmar engines, 2QM15, 2GM20 and YSM12 manuals. These engines have a max rpm between 3000 and 3600 while the 2QM20 max rpm is 2800.

2QM15: free height 36.5mm, wear limit 35mm (difference 1.5mm)
2GM20: free height 38.5mm, wear limit 37mm (difference 1.5mm)
YSM12: free height 40mm, wear limit 38.5mm (difference 1.5mm)

This pattern is quite different to the 2QM20 manual which is free height 38mm, wear limit 37.7mm (difference 0.3mm).

It doesn't feel correct...

Good thinking Wottie!
Though I'm a risk taker I don't like your pitting pics in v/v springs from the metal failure point of view. Though I'm no stress analysis engineer I can guarantee they wouldn't like pitting like that in a hardened steel spring subject to constant movement. Would be less worried about pitting on the base but in the middle of the spring it's a worry. Cheap as I am I'd probably spring for replacements, even Yanmar replacements.

[Jim Cate]

G'Day Wottie,

Couple of thoughts...

If you decide to replace the springs and the Yanmar ones are either not available or too dear, there ain't anything very special about them, and some trawling at other engine specs might well turn up acceptable alternatives, used or new.

And re the possibility of re-doing the heat treat on worn rockers, etc: pretty hard to do without knowing the exact alloy that they are made from. Getting the sequence and temperatures wrong (ie how hot to heat and how fast to quench) could lead to catastrophic failure. From distant memory, those surfaces (in the American engines I used to break) were surface treated rather than hardened throughout, and I t hink that would be hard to re-do at home.

I'd be inclined to just polish them a bit and run 'em, checking valve lash now and then. If accelerated wear appears, then replacement isn't too hard after the fact.

Cheers,

Jim