doof in idle

Submitted: Saturday, Oct 24, 2015 at 14:25
ThreadID: 130686 Views:1717 Replies:4 FollowUps:4
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recently we removed the timing gear of the front of a HJ60 2H engine to replace a leaking seal. We also replaced the rockers, they where worn with shallow pits. We left the valve tops, lifter, rods and cam as they where.
We had to remove the injection pump but it came out with it's adjusting plate intact. We didnt re-time the pump with the tube/timing marks method.
One injector line got a bit of punishment in the form of a twist. Further to the ip line twist (1st line), the first cap on top of the injector pump was loosened all the way. I carefully repositioned the spring and capped it down 3lb's short of torque spec because it was getting very tight. The other caps where also out of spec.

After bleeding it thru the glow plugs it started first pop.

But now there is a "doof" in the idle. Previous to the disassembly there was an almost unnoticeable "thun" in the idle until it warmed then it was smooth.

I don't want to think "valve" as to the cause but i need to ask, is there anything else in a diesel engine that would cause an idle doof very similar to that of a fouling plug in a pertrol engine?

Would pump timing make a difference on one cylinder
Would a fouled injector make a difference?

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Reply By: Member - John - Saturday, Oct 24, 2015 at 15:04

Saturday, Oct 24, 2015 at 15:04
G'day, make sure you haven't got the stereo up too loud, "doof, doof"........... LOL.

Sorry, couldn't resist.
John and Jan

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AnswerID: 591920

Follow Up By: LandCoaster - Saturday, Oct 24, 2015 at 16:10

Saturday, Oct 24, 2015 at 16:10
lol, & to think i been trying to win chess lately, pff
FollowupID: 860014

Reply By: LandCoaster - Saturday, Oct 24, 2015 at 17:35

Saturday, Oct 24, 2015 at 17:35
It quite amazing that writing things down frees one mind to consider nuances, tangents and odds as to which issue to start next...

double check number 1 DVH
re-check rockers' gap's
fuel pressure test between DVH and injector
crack & inspect injectors
compression test

AnswerID: 591923

Reply By: swampy - Sunday, Oct 25, 2015 at 10:34

Sunday, Oct 25, 2015 at 10:34
basically identify your cylinder and chase from there .[bleed fuel off each injector to identify the particular cylinder]

did u check compressions of cylinders wet/dry ??
[Looking for a burnt valve, poor sealing ,worn cylinder]

If the head came off the block, cylinder head valve sealing needs checking .
Worn camshaft lobes ??
Were the injector pump and injectors at least checked at a diesel shop ??[run up and checked operation ]

AnswerID: 591944

Follow Up By: LandCoaster - Monday, Oct 26, 2015 at 01:30

Monday, Oct 26, 2015 at 01:30
hi Swampy, thanks for your reply...

does it matter which end of the injector line i bleed the fuel from. The pump ends have been cracked recently, there where really really hard to crack, even with buying proper pipe spanners.
We twisted an injector line 180 degrees taking it apart, restricted flow perhaps....
No compression test yet..head hasnt come off, yet
FollowupID: 860054

Follow Up By: swampy - Monday, Oct 26, 2015 at 13:37

Monday, Oct 26, 2015 at 13:37
Twisted lines if severe enough will restrict fuel to that injector . Yes u can bleed at either end .
Diesel lines can be repaired depending upon damage .
Do a compression test wet and dry. What Ron N has suggested also with whats called a leak down tester . U can either buy one around 100$ or make your own . U will need to either connect via adapter for either injector or glow plug.

FollowupID: 860061

Reply By: Ron N - Sunday, Oct 25, 2015 at 12:50

Sunday, Oct 25, 2015 at 12:50
LC - I'd have to hazard a guess that you have a leaking valve seat - however, a partially-blocked injector can also cause noise. In general, a faulty injector will cause knocks more than a doof noise.

One always must keep in mind that it is easy for tiny particles of rust and dirt to fall into injectors, no matter how scrupulous your initial cleaning has been.
Of course, you DID clean the injector pipes and nuts down before removal, didn't you? - rather than AFTER removal, as a lot of people would tend to do.

You can check for a leaky valve by removing an injector on the suspected cylinder (or from one end of the engine, working along it, if you don't have a suspect cylinder), and by fabricating an air-tight replacement fitting, with an airline connector attached to the fitting, for the injector orifice in the head.

You then turn the engine until both valves are closed on the cylinder to be checked, lock the engine from turning, and attach a compressor airline to the fitting you have installed in the head.

Apply 100 psi (690Kpa) to the line, and any leakage past either valve will show up as air coming from an exhaust port or an inlet port.

This is an effective and proven method of finding leaking valves, and this replaces the need for a diesel compression gauge - which many people don't have anyway, and which gauge needs to read to at least 500 psi (3450Kpa), as many diesels have normal compression pressures of 325-350psi (2240-2415Kpa).

You could also have a small piece of dislodged carbon jammed in a valve seat. It's amazing how this can happen, but it does. The carbon will stay there until its hammered out, which can take some time.

However, a chunk of carbon jammed in a valve seat quite often produces a frighteningly loud knock, as well as combustion gas leakage.

Cheers, Ron.
AnswerID: 591949

Follow Up By: LandCoaster - Monday, Oct 26, 2015 at 01:19

Monday, Oct 26, 2015 at 01:19
many thanks for your reply Ron. I cleaned the area repeateadly for three days prior, made caps etc...
An unfortunate incident during dissambly led to number one injector line twisting around 180 degrees on itself on a bend, perhaps this has restricted it's flow..
The idle is really good, all cylinders poping of consistently, cept the one......
At this stage I hoping it isnt a valve, there's no knocks, everything's whiring around in there nice. There was a slight "ring" but that sorted on the 'warmed-up' second tappet adjustment.
There where substancial pits in the old rockers faces and who knows when they where last adjuted. Adjusting the tappets is difficult. The gap on two is uneven, sloped sorta', should have also replced the valve-spring retainers i spose..We've done 4 tappet adjustments after short runs, most needed tightenning each time. an now giving it a longer run hoping everything can bed in, in particular the rocker faces and sockets to push rod ball ends.
Will definetly use that method of testing for valve leaks.
FollowupID: 860053

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