Major problems with ZD30...

[pulse]

Greetings,

Agreed to help out a mate with an 02 D22 ZD30. He'd been told he needed a new head, and quoted $4,500 for the work. He doesn't have that kinda money available presently (he's had a shocking year), but desperately needs the truck running again so he can get up to Gladstone to be with his sick wife.

I took a look at it for him and found the coolant bubbling at a little under normal operating temps. Told him while it might be the head, we could replace the gasket for a price he *can* afford, and it might do the job...

Got some specs and stuff faxed over from Nissan, but failed to notice the cam bearing cap bolt torque figures weren't there until I went to tighten them on Saturday night. He / we didn't want to sit around waiting until Monday for the specs, so I made a (bad) judgement call and proceeded to torque the bearings by hand.

Engine back together and running beautifully on Sunday (turned out to only be the head gasket - w00t!), so he loads up, hooks up the boat and starts out. Half an hour later, the cops brought him back - he'd broken down 2 minutes up the road (although we drove it around for half an hour while testing). We recovered the boat and truck, and hit the key. Sounded like a broken timing chain.

Pulled down the engine, and found the timing chain intact, but the sprocket spinning on the cam gear. Broken locater dowel. Nissan only sell the dowel attached to the gear so $62 later I fit the new gear, properly torque the cams (I had overtightened for sure originally), reassemble engine and start. Idling like the chain's a tooth out. Pull it back down again to find the chain lines up properly against the sprockets. However, found that the dowel has broken *again*, allowing the sprocket this time to only move about the distance of a tooth (I had also now gotten the torque spec for the bolt that holds the sprocket and gear onto the cam, and assume I hadn't tightened that far the first time around).

I'm now extremely apprehensive to touch this engine again until I know exactly what's going on. Unfortunately, though, the owner *really* needs his truck on the road again, like a week ago

Any clues? I don't suppose any of you are intimately familiar with this engine and also located in Brisbane?

Any help at all would be very, very appreciated. Nissan won't help any more...

Cheers,
Mattt.

[pulse]

Hi all,

Update:

Had a diesel mechanic come out as a second set of eyes, etc, this morning...

We removed the glow plugs and cranked the engine some.

Verdict: 2 bent / sticky intake valves (and, of course, the broken dowel - we set up a test harness, as it were, using a cut piece of an appropriately sized drill bit today so save breaking another expensive, currently unavailable sprocket / dowel combo).

Will remove the head on Monday and replace / lap new valves, and rebuild with another new sprocket / dowel combo.

The prognosis is, basically, that on the first rebuild where I didn't have the torque specs for the bearing caps and cam sprocket bolt to hand, I've overtightened the cam bearings and undertightened (heh - I just invented a new word ) the cam sprocket retainer bolt. It all held up while we test drove it for about half an hour but, having half-loaded the truck and now towing the ~2t boat, the dowel failed when he was decelerating 2min down the road and down-shifted to second.

The second time the dowel failed was probably immediately when I started the engine after rebuild #2 - probably (but we're not entirely certain or convinced) a piston tapping a valve against a cam, or perhaps even faulty manufacturing of the dowel / sprocket assy.

Hopefully, after the *next* rebuild, all will be well...

The owner is borrowing a truck to get him up to his wife, and says he shouldn't really be complaining about a 9-day head job

Will keep y'all informed as to a result after this rebuild

Oh yeah - it's definitely the correct of the two available head gaskets

Cheers,
Mattt.

[pulse]

Finally got it apart again today (err... yesterday - I fell asleep on the couch last night, and am thus typing this at 2:30am-ish)...

Both number 1 inlet valves bent, piston is fine and looks pretty much like it never touched the valve.

Predictably (given the above), both number 4 exhaust valves are also bent. This piston certainly touched them both on the back edges of the valves, however are only marked - not scored, dented or even evidently scratched

The top section of one of the number 4 ex valve guides broke off - we didn't notice if it was already like that, or if we broke it off removing the valve (which was very tight, but we exercised great care removing it).

Perhaps indicative of the timing slipping out on the second rebuild (when we replaced the sprocket / dowel), all pistons do have a "ghosting" of the valve shapes - like all other valves were running *very* close to their pistons. Aside from the abovely-mentioned valves, though, all test out nicely.

Also, the shims of all four affected valves are scored by the cam lobes - at number 1, the scores are lobe-wide; on number 4, they're along the lobe edge.

So now we know what caused the pressure on the dowel the second time

Obviously, the head (and cams) now needs to be tested more thoroughly, and a new valve guide fitted. My best guess is we'll be putting it back together next week sometime. I'll let y'all know

Cheers,
Mattt.