kubota 800 hour engine valve adj maintenance=worth it?

[dperkins]

I don't care if you do it everyday. What I do care about is whether something is right or not. I give advice to mechanics everyday too. That doesn't mean I'm not full of false information and wrong most of the time. I do my best though.

I believe what I said is correct. I believe what you are saying is incorrect. Neither of those gives me any particular pleasure. I don't really care to get into a spat about it either. I wish you great success in your field of endeavor.

Good point. As the lash tightens you'll actuall have slightly improved engine performance with all other things at factory tolerances. You'll have more time with valves open. On high performance diesel engine valve lash is set tighter than factory specs to take advantage of this improved airflow. Granted these are turbo charged engines. Just my $.02

 

[jonyyuma]

Stang, there was an error in the third paragraph...The valve does not get struck 4 times a revolution...I too have adjusted valves on a turboed diesel..They get tighter with time and mileage. Plus no-one said any thing about the noise a diesel piston makes until it gets hot and expands, to better fit the bore.. Or???

 

[jonyyuma]

Kuboman, you weren't the only one to have GP trouble with a Gm motor..My 6.2 PU took to eating the glowplugs, even having one Melt off and fall on top of a piston while driving home..I read most glow plugs operate at 6 volts or as high as 9 volts. this is to make them heat up very quickly.. My Kubota doe not need to have the GP circuit used very often. If I was going to start it in very cold conditions i would use it for a better start and a quieter idle. I always used them on my Isuzu 2.2 diesel and my MB 3.0 td...

 

[jejeosborne]

Yes, valves only seat once every other rotation. That is 8 times fewer than stated. Someone needs a refresher class. I adjust my own motorcycle valves but haven't needed to on my b7800 yet. I am leaning towards a bad GP and thus the extra smoke from the "dead cylinder/s" at startup.

 

[namesray]

Yes, valves only seat once every other rotation. That is 8 times fewer than stated. Someone needs a refresher class. I adjust my own motorcycle valves but haven't needed to on my b7800 yet. I am leaning towards a bad GP and thus the extra smoke from the "dead cylinder/s" at startup.

that is what i am leaning towards too, but the dealer doesn't think so at first. might find out soon as i am trucking it over to them tommorrow to get the valves adjusted this comming week. as if that will fix the problem, i don't know and probably won't know until i start it on a cold morning again and it has been starting normal as we have been having warmer temps here lately and are going into summer.

i will also find out if the valves are out of adj bad or not at 900 hours and report back.

 

[SPYDERLK]

There are a couple mis- conceptions in this thread. You thought because it started then the glow pugs should be operating?! Not necessarily true. One could be working and that is why it fires, but runs rough for a few seconds until the air heats up. Remember a diesel engine just runs off of compression ignition. There is no spark to ignite the fuel/air mix. So if it is cold, cold air is much denser and also has a higher dew point (moisture content).

Both my Kubota g1900 (three cylinder) and my 2cyl Mitsubishi do the same thing. Starts, and puffs a little until you get some heat in it. Takes Longer to warm up the colder it is...

Now, for the valve adjustment. At work(generator rental company) we have Kubota 15kw generators. We do an overhead valve adjustment every 2000 hours along with testing the injectors. The whole purpose of adjusting the valves isnt because they are "loose". Think about the valve slamming back into the seat, four times per revolution. Now think about how many times the valve has slammed back to the seat in the last 900 hours.....

As the valve and seat wear, the valve tip becomes raised. So your valve clearance will tighten up over time causing both the intake valve and exhaust valve not to fully open. This means the engine won't take in as much air, and can't expell the burnt gases as efficiently. The engine will still run just fine, but it will start to loose peak power. We are not talking much in terms of clearance... Just a couple thousandths. But on the other hand, it is very possible too that the rocker has loosened up. This is normally due to someone not tightening something to torque more than from just coming loose on it's own.

1] Valves do not slam into the seat. There is a deceleration profile on the cam that lowers them gently the last few thousandths. As seats wear and clearnces tighten the valves seat more and more gently. There can come a point when valves become a little tight, where rocker assembly wear becomes very near the combined wear of seat and valve. Valve clearnces can then be stable over thousands of hrs.
2]Valves open further with tight clearances. The very 1st thing you will notice with tight valves will be issues at extreme lo speed and throttle. ... Starting and idling. Hi speed operation will be fine.
larry

 

[Freakingstang]

Stang, there was an error in the third paragraph...The valve does not get struck 4 times a revolution...I too have adjusted valves on a turboed diesel..They get tighter with time and mileage. Plus no-one said any thing about the noise a diesel piston makes until it gets hot and expands, to better fit the bore.. Or???

Yeah... I guess I had a bad day.... total brain fart there...

The amount of compression (static compression on a diesel is usually 18:1-25:1). With more pressure, there is more heat, so the pistons have looser tolerences.

Also since I was wrong... I'll add that sometimes the clearance depends on where it is actuated by a hydraulic lifter or a direct cam follower off the cam. there can be alot more forgiving tolerences in a hydraulic setup.

As far as tighting clearances improving performance, I can't verify that. I have not messed with diesel truck perforance. All I know is from experience. If I have a 300kw with a cummins QSM11 with a valve adjustment out, it still starts and runs just fine, but will not pull full load on our load banks. it is more apparent on the smaller generators. our 15kw kubotas will only pull about 9-10kw when valves need set.



Either way, sorry I spouted out.

 

[Chilly807]

I'd lean towards a glow plug myself. If most of them are fine, it'll start normally on those, and struggle with the dead ones until the cylinder warms up a bit more.

You can try starting it without them at all, and see what happens. If the problem is much worse, then it's worth checking them.

Sean

 

[BXpanded]

Valve adjustments are necessary for engines with solid lifters. As has been mentioned, valves and valve seats wear. Clearances get tighter. When the clearance gets too tight, the valve cannot close completely and begins to leak. The leakage results in lower compression. However, the real problem results from the hot gasses leaking by the valve. That exposes the valve and the seat to a high speed flow of very hot, burning fuel/air mixture which tends to overheat the valve causing burning of the valve and damage to the seat.

Someone also correctly mentioned that the head of the valve is cooled by conducting heat to the water (or air) cooled head. If the valve cannot close completely, little heat is transferred, and the valve gets hotter still. As the valve gets hotter, the thermal expansion of the valve causes it to be held even farther from the seat, resulting in even greater rise in temp, and even more valve leakage.

Valve clearances are normally set with a cold engine. As the engine warms, the valve and valve train parts expand and the clearance is less. Some engines have a spec for HOT adjustment. This hot clearance is always less than the cold clearance as the cold clearance spec has an allowance for the expansion. Adjusting valves hot is pretty uncommon because it's difficult to keep everything at a consistent temperature. It also isn't fun.

Gain or loss of a .001-.002" of valve lift makes no discernable perormance difference.

Also previously mentioned, the cam has carefully designed ramps to accelerate the valve as it's opening, and to gently set it back on the seat when closing. If the clearance is too great, the lifter essentially passes over the acceleration ramp and hammers the valve open. On the closing side, the valve slams back on the seat without the controlled deceleration of the closing ramp.

Mis-adjusted valves are not to be ignored. Whether or not the OP's tractor needs adjustment... Who knows without checking. If you check them you might as well adjust them. I would think someone at the engine manufacturer had some reason for the 800 hour schedule. Then again, it might just be a number picked out of the air.

As for the rough running at start up, I doubt the valves are the problem.

 

[namesray]

well, got the b7800 back today. the dealer got the valves adjusted and fully tested the glow plugs. the glow plugs were working fine. only thing is the amps were a little less at plug. dealer said that could run a new cable to give better current, but not really worth it at this time.

on to the valves. just for everybody's record, my kubota engine did need adjusting at 895 hours. they weren't terrible, but here are the numbers.

#1= ex .010 in .0085
#2= ex .0105 in .010
#3= ex .009 in .007
#4= ex .0105 in .0085

specs for v-1505 e2 d16 diesel engine are .0057 to .0073

all valves are now .007

engine seems smoother, but might be my imagination. i also haven't run it much, only to and from the trailer to the shed, where it will now get its 900 hour pm. (oil, hydraulic, etc.)

as far as it starting hard in the cold, have to wait for a cold day. dealer said everything seems fine and will just chalk up future small hard cold starts to normal wear and tear=895 hours. can glow plug it longer if feel the need. 15 to 25 secs.

dealer said it was worth it to due the valve adj, atleast for me. tractor actually came back cleaner then when i took it, and i washed everything just before i took it and i am fussy too, so dealer did a great job, and i will be taking the tractor back around the 1500\1600 hour mark to do the valve adj again and the 1500 hour fuel injection nozzle injection pressure check. do them both at the same time to save a trip.

i will try to update ,if i remember, starting on a cold day if the valve adj did anything to fix that cold start problem.