Look'n up to see the bottom

[OlTrailDog]

The saga continues. After many delays including finding out the old head was cracked; having to order a replacement head... twice; having valves and seats ground; water flange mis-match taken care of; head themometer size mis-match; and waiting for miscellaneous parts to arrive, e.g. OFI injectors, and etc., the L345DT is finally back together.

Small problem in that it doesn't start. Bled and re-bled fuel lines...nope. Whitish smoke out pipe, but no firing, not even close. So I decided to recheck the valve lash...looked fine. Thought I should do that before doing another compression test. Bottom line is the compression is now basically 200 per cylinder, 90 lbs. less than before I started on this project at 290 per cylinder with a cracked head and leaking valves .

The pre-wet/dry compression test indicated head/valves as did the leak down test. I mic'ed the cylinders twice with two different cylinder bore gauges (a SAE and a metric). The cylinders were within spec for both taper and out-of-round.

So, before I start a complete dismantle to redo the bottom end I thought I would run it by you folks for a small miracle that I am overlooking something simple, stupid, or simply stupid.

Miscellaneous Info: Existing engine V1501-DA. The Kumar Bros head is a V1501 and with the exception of the half water flange versus the old full front water flange and an extra stud hole on the front exhaust side (that I discovered when coolant started pouring out) the head looks the same.

The full gasket set was that I purchased was for a V1502 since it was the same price for the full set as a V1501 that I could find. I checked the head gasket for a match before installing and they certainly looked the same holes and metal parts. Albeit I didn't mic the head gaskets to see if there could possibly be a difference in thickness. If the new one was thicker it is conceivable that could cause a compression difference. There were no head shims in the old head gasket set up. The head bolts were torqued to spec in three sequences to 56 ft. lbs.

Worse case scenario: If it is bad rings and I forge ahead with dismantling the bottom end I have several options. Since the cylinders were within spec I may get by with rings...or go with boring out to oversized...or new liners and rings. I think I read somewhere that even if you install liners, the new liners need to be bore to spec.? This is assuming piston will either be in spec or replaced.

blah, blah, blah, and so forth. Is that small violins I hear?

 

[Tooljunkie]

Recheck valve setting. . 290 psi before tells me someting has changed. Must be some kind of head gasket specs somewhere.

 

[MagKarl]

Any chance valve timing is incorrect?

 

[OlTrailDog]

Anyway to check the valve timing without pulling of the front of the tractor to see the timing marks on the cam gears?

When the timing marks on the flywheel are lined up, i.e. TC 1/4 and TC 2/3, the correct valves on the cylinders are completely closed and the valve lash is within spec .008 (.007-.009 spec).

 

[Bluegill]

Sounds like the problem isn't in the bottom end?

 

[OlTrailDog]

A few rambling thoughts: Perhaps the rings are bad. There was no change in the wet/dry compression test. The oil was injected via the glow plug hole. However, perhaps since there is a pre-combustion chamber and the small amount of oil (1 ml recommended because of the possibility of disasterous probems doing a wet test in diesel engines) the oil never really sealed the rings to create a difference in compression results.

Perhaps, the leak down pressure from the rings was missed (out the oil fill and breather tube) because it was far overshadowed by the noise of the leaking air from the exhaust due to the cracked head and leaking valves.

Even though the cylinders are within tolerance, the rings could still be bad.

However, none of this explains why the compression difference between the pre-head job and the new head tests.

Possiblilities: the head gasket and/or the new head tolerances are different enough to create the differences. I didn't stick a "lead" wire down through the precombustion chamber into the cylinder chamber to check tolerances (manual instructions) because it seemed like to much of a hassle and because the only lead wire I know of is soldering wire and I didn't want to crush and break off a piece inside the cylinder. I asked about lead wire at the parts stores and no one was aware of any.

From Manual "To check piston to head
clearance, insert a soft lead wire
through injection nozzle holder hole.
Rotate crankshaft by hand until lead
wire is fiattened by piston top. Measure
thickness of fiattened wire to determine
top clearance which should be 0.7-0.9
mm (0.028-0.035 inch)."

I just made sure there was no valve contact when setting the valves and decompression adjuster when turning the engine by hand.

Perhaps I could remove the head and check with some plastigauge. I would reuse the same head gasket since the engine hasn't been run(?)

The new injectors came with new crush washers and have been torqued to spec (30 ft. lbs). There is an injector top nut that was loose in order to align the two barbs on (ND injector 1570) with the small hoses that run between the injectors, pump, and tank return (overflow hoses). After aligning the hose barbs I tighten the top nut. Is it possible there is a leak because the nut isn't torqued tight enough to prevent a leak (most likely not, but a thought).

I know I can of ramble on, but I'm trying to provide sufficient information to figure out this perplexing problem.

 

[North Idaho Wolfman]

If you truly want to make sure it's a ring issue, unload the valves, loosen them all the way up and do a compression test if the #'s go up then it out of time and yes you going to need to pull the gear case to check the gear timing.

 

[BadDog]

I have no idea if this applies to this head, but even if the head cylinder chamber shape is the same, chamber volumes can change quite a bit and still look the same. If the new head has a larger cylinder chamber volume, that would drop your compression. Again, no idea if that is relevant here, and may not even be possible, but it's another place to look that crossed my mind reading this.

 

[OlTrailDog]

Okay, I gave the Wolfman technique a go, i.e. removed the push rods from one cylinder at a time to completely release the valves. I did this for a couple of cylinders (2 and 3).

The results: 75 lbs psi. The pressure slowly builds and levels off at roughly 75 lbs.

Now help me figure this out. Is this because:
1) the rings are bad and air leaks out past the rings.

2) the rings are bad enough that they do not create enough suction to draw air into the cylinder past the valves. The more the pressure builds into the cylinder, the additional air can be sucked in to build pressure.

3) the rings are okay but can not suck air into the cylinder through the newly machined valves or past the rings in order to build sufficient compression.

4) Pressure definitely doesn't build past the 200 lbs psi. as would indicate a valve timing problem, as per Wolfman. Timing marks unknown. However, knowing that the tractor ran prior to the head job should indicate the timing is either on, or close enough for the tractor should run now. That is to say, nothing has been done that would change the pre and post timing.

General gripe: Why did they have to put the power steering oil tank in such a location to necessitate removal in order to remove the rocker cover? Great engineering fore thought. Plus, if you don't re-install it the pump squirts oil out when you turn the engine over. Don't ask me how I learned this.

 

[ShaunRH]

Okay, I gave the Wolfman technique a go, i.e. removed the push rods from one cylinder at a time to completely release the valves. I did this for a couple of cylinders (2 and 3).

The results: 75 lbs psi. The pressure slowly builds and levels off at roughly 75 lbs.

Now help me figure this out. Is this because:
1) the rings are bad and air leaks out past the rings.

2) the rings are bad enough that they do not create enough suction to draw air into the cylinder past the valves. The more the pressure builds into the cylinder, the additional air can be sucked in to build pressure.

3) the rings are okay but can not suck air into the cylinder through the newly machined valves or past the rings in order to build sufficient compression.

4) Pressure definitely doesn't build past the 200 lbs psi. as would indicate a valve timing problem, as per Wolfman. Timing marks unknown. However, knowing that the tractor ran prior to the head job should indicate the timing is either on, or close enough for the tractor should run now. That is to say, nothing has been done that would change the pre and post timing.

General gripe: Why did they have to put the power steering oil tank in such a location to necessitate removal in order to remove the rocker cover? Great engineering fore thought. Plus, if you don't re-install it the pump squirts oil out when you turn the engine over. Don't ask me how I learned this.

Your 75# reading doesn't jive with your 200# reading.

I'd think you have to test with the cylinder open to air via the glow plug hole and an BDC (Bottom dead center) then install the compression gauge. You should get a good reading with a single trip to TDC.

 

[MagKarl]

I think you need the intake valves to open, as it normally takes several revolutions to maximize pressure on a compression test.

I also think it would be worth it to compare old and new head gasket thicknesses and chamber volumes.

Any chance the decompression is rail is involved? Have you verified that clearance?

 

[OlTrailDog]

The #75 reading is with the valves closed, as per Wolfman's suggestion. But that is why I ask the questions. Because I can't quite wrap my head around how it all works with out the intake valves letting air in, especially as compression builds (up to #75) further working against letting additional air leak around the closed valves and rings. In normal compression tests the air comes in the intake valves building pressure in the tester that can't escape because of the one way Schraeder valve in the adaptor until you release it.

As MagKarl noted it takes several revolutions (and revolutions at sufficient rpm) to get a valid compression rating.

I had hopefully considered the decompression mechanism. But I had adjusted the decompression mechanism to spec, i.e. TDC, touch rocker arm, and turn 1 to 1.5 turns (I used 1). Notwithstanding when starting or checking compression the decompression mechanism does not engage the rocker arms because when the decompression mechanism is disengaged the adjustment pins are pivoted completely out of the way and can not engage the rocker arm tops. I am confident of this because when adjusting the mechanism I could poke the screwdriver into an adjacent adjuster hole and move an adjacent exhaust rocker arm, i.e. it was not at TDC and loose.

Last night I thought that I should do a quasi leak down test. I won't bother with the gauges. I'll hook some air up to the glow plug adaptor with Schraeder valve removed, pump some air to the TDC cylinder, and listen to see if the escaping air is coming from the exhaust (valves) or from the crankcase.

 

[ShaunRH]

The technique I described will let you get close enough to a full compression test to be useful. By installing the gauge at BDC you already have enough air to get you to about 95% of what a full rolling test would give you.

Personally I'd static time the engine just to make sure it was in time and then run the compression test. Also, crank it over with the valve cover and manifolds off. If you get delayed pressure release or early pressure release, that will tell you your valves aren't in time.

 

[North Idaho Wolfman]

Are you getting the same # reading on all cylinders?

The extreme drop in the compression #'s tell me that the volume in the cylinder is too large, this could be from head gasket being too thick, and when I say too thick it would be less than the eye could see.
The other option is the pre chamber size, and relief space are too large.
Do you still have the old head there?
If you do it might be worth it to pull the head and have the 2 volume matched, very slight volume differences make a huge compression # difference.

This one is tricky because with the change in the head and head gasket, too many variables are at play to say that "yes you have bad rings".

 

[OlTrailDog]

I pulled the head. There is a definitive difference in the head gasket thickness. The old gasket was .05 inches and the new gasket is .075 inches, or a difference of .025 inches. This difference is enough to be easily seen.

Volume difference equals 2881 cubic mm or 2.88 cc or .002 difference in total volume, i.e. 1439.88 cc versus the nominal 1437 cc. The big question is if this is enough difference to drop the compression??? Hopefully so, because the other options are not very appealing, eh?

The heads are completely flat except for the relief for the valves. That is, there is no "dome" typical of gassers. Therefore, any difference in head volume would have to be in the precombustion chambers (as Wolfman mentioned). Since the precombustion chambers are blind, I'm not sure about the volume differences. Would it be best to take it to a machine shop to answer this. Or do I plug a precombustion with an injector and glowplug and then use a syringe to check difference in the volume required to fill each with a volatile fluid. Hopefully this wouldn't be the scenario, because I don't see anyway of remedying this if there was a difference, except to purchase another head! And that could be a crap shoot too.

Next step from here: Any thoughts on the volume differences and the compression differences. Any suggestion making sure I get the .05" gasket versus another .075" gasket? Better yet, where do I get a gossamer thin gasket that boosts the compression to like new!

 

[OlTrailDog]

Forgot to mention, I hooked up about #70 air to one of the cylinders at TDC (both valves completely closed and .008" lash so I know they were seated and not a timing issue) and listened where the escaping air was most noticeable. Although I could hear the air in the exhaust pipe and oil fill hole, the most noticeable was the air intake.

Finally, to answer Wolfman's question about if the values were across cylinders. They are for 2, 3, and 4 as 1 is simply not worth the hassle being behind the injection lines every time to check something (great engineering feat, like the power steering oil tank). Since the others are very close readings I figure there is nothing to gain by the hassle of finding out what 1 is. Also, 4 had the worst mic tolerances, albeit still with spec.

I suppose the best course of action is to locate a replacement thin head gasket. Put it together. Check the compression values. And decide the next course of action from there.

 

[MagKarl]

I would definitely measure the head chamber volume. I would think a syringe would be fine for a gross check. I'd just use fuel if it was me. I know the gasket thickness doesn't seem like much, but it may be a larger player percentage wise on the squish volume. Hard to say from here having no idea what the chamber actually looks like.

 

[North Idaho Wolfman]

Yes measure the pre chamber volume.

 

[OlTrailDog]

Okay, the volume of the pre-combustion chambers on the old head was 13 cc. The volume on the new head is 15 cc. Therefore the total difference is 4.88 cc per cylinder.

I ordered a new head gasket from the local Kubota dealer. I explained the difference in the thickness of the original versus the gasket kit head gasket and that the reason I was going to pay more for it locally was that if it wasn't a .05" gasket I wasn't going to purchase it.

So, the 2 cc difference in the pre-combustion chambers??? I suppose I just drop a glob of JB weld down the injector hole and call it good. Oh, better yet, I'll put the glob of JB weld on top of the piston and have a hemibota.

Now seriously, I can't imagine any other way to decrease the volume of the pre-combustion chamber without adding mass to it, say a ball bearing. I can't imagine machining the head would sufficiently decrease the volume. Plus, then the valves banging the pistons would become an issue.

At least we have figured out the probable cause of the compression discrepencies.

 

[North Idaho Wolfman]

Okay, the volume of the pre-combustion chambers on the old head was 13 cc. The volume on the new head is 15 cc. Therefore the total difference is 4.88 cc per cylinder.

I ordered a new head gasket from the local Kubota dealer. I explained the difference in the thickness of the original versus the gasket kit head gasket and that the reason I was going to pay more for it locally was that if it wasn't a .05" gasket I wasn't going to purchase it.

So, the 2 cc difference in the pre-combustion chambers??? I suppose I just drop a glob of JB weld down the injector hole and call it good. Oh, better yet, I'll put the glob of JB weld on top of the piston and have a hemibota.

Now seriously, I can't imagine any other way to decrease the volume of the pre-combustion chamber without adding mass to it, say a ball bearing. I can't imagine machining the head would sufficiently decrease the volume. Plus, then the valves banging the pistons would become an issue.

At least we have figured out the probable cause of the compression discrepencies.

Are the prechambers inserts, most of the older heads are designed that way.
If they are, you could swap the pre chambers to get the right volume on the new heads.