Intake Lash Closed Itself?

[cjmmbrock]

Has anyone ever heard of the intake valve lash closing by itself?

I'll make a long story short, and say I'm trouble shooting a 3 cylinder Yanmar. The last time the engine ran, it overheated, then wouldn't start. When motoring the engine, all 3 intake valves allowed cylinder pressure to come back through the intake. I figured I hurt the valves as a result of the overheat. Before removing the head, I checked the lash and noticed the intake lashes were all 0 if not negative. Thinking this may be holding the intake valves open during the compression stroke, I set the lash at .010 and now NO compression comes back thru the intake.

Could the overheat have cupped the intake valves, and closed the lash? I'm tempted to reassemble and see what happens... Anyone ever heard of this?

Thanks,
Chris

 

[brandoro]

If the valve/seat wear is greater than rocker/lifter wear the lash would be reduced. I would say unusual but not impossible. Since you found that and corrected it I would reassemble and try it before going on with more disassembly, time and expense. It is quite possible that the lack of valve clearance was the cause of the overheat and not the result of it.
How bad was the overheat and how many hours on the engine? My first tractor had no temperature gage, the owners manual said to watch for steam, if steam issued from the engine it was running too hot and you should reduce load. If your overheat only made a little steam I wouldn't worry, if the overheat means it was run completely out of coolant and was crackling hot then there probably is other damage.

 

[Scotty370]

I think we need the 'long' story! What happened when you let the thing completely cool? You still had open intake valves on the compression stroke? Have you run a compression test after your .010" adjustment? New, or 'new to you' tractor? Make/model? Lots of us with tech manuals out here! ~Scotty

 

[cjmmbrock]

Thanks for the replies guys:

I don't think the overheat was all that bad. It was low on coolant, but not dry. The engine would run fine, but as soon as I put a load on it, it would die. It did this 2 or 3 times, then wouldn't restart. As far as hours on the engine, it's a mid 80's JD 750.....this is my first tractor, hour meter has been replaced, etc. etc. you guys have been here before I'm sure It's safe to say it has alot of time on it, but I don't know exactly how much. Just like your first one Brandoro, it doesn't have temperature or oil pressure gauges. It does have lights, for low oil pressure and high water temp...but they were both extinguished. I haven't yet tested the senders though.

Oh yeah, this tractor is new to me...I put around 10 hours on it in the spring. The overheat happened 2 weeks ago.

Scotty370 the only thing I can add to tell the entire story, is that when trying to restart it the last time. It sounded like it was trying to fire....maybe on one cylinder. It didn't act "tight" like it was trying to seize or anything like that. I don't know if the intake valves were open on the compression stroke, but it seems so. I couldn't fit my smallest feeler gauge (.008) underneath the rocker arm nor could I feel any play in the rocker arm. I picked a number from the sky .010 and set them at that. Now when I motor the engine, I have no compression back thru the intake. I have a leakdown tester for gasoline engines, and wanted to do a leakdown, but gave up on removing the injectors. I'm guessing the entire injector body unscrews from the head? It sounded easy to remove at first, but when the injector body unscrews, the boss where the fuel line screws into the injector body hits the studs that are mounted beside the injector. I know that doesn't make sense....I'll post a pic of it when the camera charges. Also, do you know of an adapter to use an automotive (14mm spark plug thread) leakdown tester?

 

[Soundguy]

harbor freight sometimes had diesel compression test kits for pretty cheap.

soudnguy

 

[Just Bill]

While the cam timing might be off, and it would cause starting problems.
The cam timing would not cause a problem with the valve lash.
Valve lash can have an affect on valve timing, by causing them to open too early or too late.
I would guess that the valves are sinking into the head which is normal and have probably never been readjusted before now. The problem can be compounded by running hot.
You will probably will end up with the head off and doing a valve job and while you are at it you can clean the cooling system which probably needs it.
This is just my opinion and hope it helps.
Good luck.

 

[dfkrug]

Before removing the head, I checked the lash and noticed the intake lashes were all 0 if not negative. Thinking this may be holding the intake valves open during the compression stroke, I set the lash at .010 and now NO compression comes back thru the intake.

Chris, it sure sounds like your valves are not fully closing anymore. This
can happen when the valve wears into the seat, which limits the
compression. It will also burn the valves since they can no longer cool
from contact with the seat and hot gases blow right by them on the
ignition stroke. This is what happens when the engine gets older and the
valve lash never gets adjusted, as JUSTBILL says.

I have had this happen to gas engines before...you need to catch it
quickly before the valves are burnt.

I do leak-down tests on gas engines, but never diesels, since I have
no adapters for the injector holes. Getting your injectors out is tough,
but none of mine have ever been threaded. Gunk and rust is what keeps
them from sliding out. Try twisting them back and forth between the
studs, while pulling up.

 

[cjmmbrock]

Thanks for the replies guys. I was able to get the injectors out (they slid out with a little force and twisting), thanks for the tips!


Just Bill, you were right on the mark....I pulled the head today, and it appears the head gasket failed. Had a bunch of crud on the #1 piston. I checked the head and the block deck for cracks, and didn't see any. I plan to lap the valves replace the head gasket and see if that gets the cylinder pressure back up where it needs to be........Oh yeah, I forgot to mention. #2 and #3 cylinder pressures were both 280-290 psi.......#1 was 85

dfkrug, I don't blame you NOW for not doing the leakdown check, lol. I made 3 adapters from 1 1/8" steel rod stock. I cut them 2 1/2" long drilled a 1/2" hole all the way thru, then threaded one end for a gasoline type spark plug (14mm x 1.25 pitch with a small 45 degree shoulder inside). The reason I don't blame you, is I shoulda just removed the head rather than wasting time making the adapters...

 

[dfkrug]

dfkrug, I don't blame you NOW for not doing the leakdown check, lol. I made 3 adapters from 1 1/8" steel rod stock. I cut them 2 1/2" long drilled a 1/2" hole all the way thru, then threaded one end for a gasoline type spark plug (14mm x 1.25 pitch with a small 45 degree shoulder inside). The reason I don't blame you, is I shoulda just removed the head rather than wasting time making the adapters...

The Diesel engines I rebuilt were so far gone that there was no doubt they
had to come apart. No need for a leakdown test!

 

[Just Bill]

It will cost a few bucks but you will be better off taking the head in and having it reworked.
They should cut the valves, seats and knurl the guides.
They should mabnaflux to check for cracks, check for flat and clean out the water passages.
This is what I would do if it were mine.
Future engine problems wont be the head.