diesel woes

[Guest 000]

My engine is a Perkins Parama M30.

In neutral I can select any rpm I like and the thing just sits there purring away to itself. In ahead gear though it is a bit different. Up to 1200rpm it runs well. Between 1200 and 1600 rpm it has a 'miss' every couple of seconds or so. From 1600 upwards she settles right down.

There is no exhaust smoke, the 'miss' is only milliseconds with no measurable change in rpm. At first I thought my brand new gearbox was misbehaving. In a complicated manouvre I was able to put my shod foot on the prop shaft and exert quite a bit of pressure through all different revs. From this I learned that firstly the box isn't slipping and secondly you shouldn't really do this because your foot is liable to slip off the shaft and peel all the skin on the back of your ankle.

I am thinking that maybe it is a governor issue at those revs, or maybe injectors and high pressure pump need servicing. The injectors were last done 3 years ago by a man in Thames who seemed bewildered by the whole job. I don't know when the high pressure pump last had any attention.

Any thoughts gratefully received.

[Island Time 1,239]

Sounds like a fuel issue - not familiar with that particular engine, but I presume it is a mechanically governed one? If so, it could also be a sticking governor - restricting fuel at set revs, then moving again?? Pump and injectors could also be the culprit though..

Faults like this can be a B&^%H to isolate and repair.

Sorry

[waikiore 400]

My guess would also be fuel related, check all filters first as that could be restricting the engines ability to respond to load changes.

[Guest 000]

Thanks for the replies.

Given the fact that when you open the throttle, the engine is a bit,I suppose you'd call it wavery, before it settles on the increased rpm, I think the govorner is possibly the culprit. I will take a berth in HMB marina for the next month - can anyone recommend a good (and not too expensive) firm for pump and injector servicing in the Auckland area please?

[erice 732]

when bought Vindil's small vetus/mitsubishi diesel would only run at a lumpy idle

 

 

no matter where the throttle was..................

 

the diesel pump and 2 injectors went in to

 

diesel services, 120 penrose rd. auckland 1060,        

 

http://volpower.co.nz/dealers/diesel-services-auckland-ltd-penrose/

 

where they were stripped, rebuilt + tested for a total of $340 

 

the mechanic noted that was virtually no wear on any of the parts.... 

 

the problem turned out to be no compression on the front cyl, due to the big end shell bearing being MISSING

 

 

quotes for a full strip, + rebuild seemed to range from $2000 (hone the scratched bore)  - $4000? (rebore to 1st OS)

 

but as the 2 biggest parts of the vetus heat exchanger also needed replacing

 

a new engine was imported and DIY'd in for $7000 - $1000(sold new gearbox) = $6000

[wheels 543]

Wooooo up the Horses Chris. Lets step through this a little slower. First question,

Has the engine done the same hrs as gearbox... was it 150hrs??

Is this occurring both out of gear and in gear and both forward and reverse?

Diesels are really simple in operation, but a damn pain in the A as far as technicality and expense goes, most especially when it comes to the Injection system.
Firstly, these engines are little beauties. Capable of very high hrs for such a little engine.
The Injection pump is a Bosch and the governor inside it is mechanical. So the chances of it causing a miss is pretty remote. In fact, I can't really think of anything that could cause it to miss in the way your describe re the governor or for that matter, the injection pump full stop. Anything causing a miss would cause much more serious running issues. Same goes for the Injectors.
Yet very peculiar that you are getting this situation at a particular range of revs. that has me a little baffled.
 

[wheels 543]

Oh and be really careful with rotating shafts. I have seen a safety vid of a guy getting his shirt ripped clean off him when it wrapped around a spinning part of a lathe. And have any of you seen the latest vid doing the rounds of a guy being sucked into a Paper manufacturing machine. He must have been a newbie and watched a foreman put his hand on the paper as it was feeding through the rollers. This guy followed suit, but his hand was a lot higher up toward a feed roller. The paper is flying through at a horrific speed and the guy gets his fingers caught in the roller, which instantly takes his arm dragging his entire body right through in a split second. He was instantly killed.

[Guest 000]

The engine runs very smoothly out of gear at all revs. The 'miss' is only when in ahead gear and between 1200 - 1600rpm. I cannot determine any change in engine rpm during the misses but the engine shakes on its mounts. I don't know if it does it in astern gear - we have never run it long enough at those revs to determine it. The engine is about 5000 hours and the gearbox new, 16 hours.

[Black Panther 1,591]

Wheels I need to talk to you about the sort of videos you are watching. What ever happened to Lassie?

[Guest 000]

When I changed the gearbox I didn't change the damper plate. It is three years old and looked OK, all the springs still tight etc, but a possibility of failure causing the problem?

[Island Time 1,239]

Chris, test it ahead and astern. Important to know. Is it really a miss, or a shock load transmitted through the drivetrain? Sometimes you can hear which by listening carefully to the exhaust.

The difference between loaded ( in gear) and unloaded is mostly fuel quantities.

If it's a damper plate or other drivetrain issue it may well only do it in one direction.

Sounds like you need a good engineer to isolate the issue before guessing and potentially wasting lots of $ needlessly.

[Fish 0]

Drive damper plate deals with torsional vibration of the engine from the drive chain. Their primary job is to prevent gearbox chatter at low revs.

If you engine shakes like a bastard at the mid rev range and only in gear - did you re do the alignment and engine mount adjustment after installing the new gearbox?

It wouldn't explain the "miss" sound, but every other system you described sounds like either poor engine alignment, old engine mounts, or even a broken engine bracket. I.e. Excessive vibration at 1,200 to 1,600 rpm then settling down. those faults would also give bad engine vibration, but we did have a broken mount bracket and didn't notice until trying to un bolt the mount, despite studying the engine carefully AND getting a professional mechanic to assess the engine for faults related to noise and vibration...

[Guest 000]

The four engine mounts are on the engine only, nothing on the gearbox. So no, I didn't recheck the alignment. Good point on the engine mounts though. They are pretty old. When I said that the engine was leaping around on its mounts in the 1200 - 1600rpm range, this is not continuous. It only gives a shudder that corresponds to the 'miss.'

[Guest 000]

What about cavitation? The prop of the H28 is in an aperture and I know that the tip clearance is a little less than recommended.

[Island Time 1,239]

That could well be it Chris, check the engine mounts, alignment, cutlass bearing etc.sounds to me like it might not be a real " miss" at all. How much tip clearance do you have?

[wheels 543]

Sorry I didn't get back to this last night, I got engrossed in watching a re run of Lassie

Pretty much 999.999% positive you can rule out fuel, or anything at the engine running end of the list of possibles.
I am as much sure you can rule out dampening plate as well. The plate drive spline should be solid if you tested it by hand before bolting up box. But a loose set of springs causes a rattle rather than vibration. At 150hrs, I am not worried that you did not replace it. The plate is designed to take out Injector shock at idle and shock from gearbox when it engages.
Are you tied to the dock when testing, or moving? It is quite possible to have cavitation if you are tied up, as the water sucks past the Hull unevenly.
Have you got a folding prop?
How clean is prop?  no matter whether fixed or folding
As you said, check engine mounts, but I suspect something more toward the drive end. How aligned was the gearbox drive flange to the prop shaft? did you need to move the box much to get it aligned for the bolts? There should be very little moving around to align. A little is allowed but not too much. And as bolted home, it should have come up pretty much flat to flat of the plates faces. Did you remember to tighten the bolts fully? Hey, even the experts have forgotten simple things like that. I'm really glad I'm not an expert and to have made silly mistakes like that
 

[too_tall 15]

I have had a somewhat similar miss in a stationary diesel engine once - albeit a 300hp one attached to an effluent pump. It was a fuel problem, and it was the pressure switch in the supply pump was faulty and not turning the pump on when it should. At unloaded, the engine had sufficient fuel pressure reserve in the filters etc that the pump would supply fuel again before starvation occurred. Under load, at high RPM the supply pump never shut off. At low RPM, again, enough reserve. But at around .5 - .75lpm fuel demand resulted in the fuel supply pump still cycling off, but not sufficient reserve in the fuel system to keep fuel supplied to the injector pump.

 

I would tend to lean away from it being a fueling issue, but it could be. A lot depends on just how those engines feed the injector pump. I have no experience with one so can't comment further than this. 

 

As a suggestion, put your ear near the exhaust, hopefully you can hear if its a genuine miss vrs a sudden "shock" loading causing the perceived miss.

 

Did you comment as to the regularity or frequency of the miss? I might have missed it if you did.

[Guest 000]

We are at anchor at the moment.

I have no concerns about alignment. When I put in the new box everything fitted easily including the prop shaft/gearbox flanges. I have an RFD flexible coupling between, in good order, and feeler gauged all around - all well within tolerances.

Tip clearance should be 2.5in and I have 2in. I need as big a diameter prop as possible as the prop is shielded behind the Deadwood. According to Bri-Ski the reduced tip clearance won't matter as the hull shape above the prop is very acute, curving upward each side at about a 45° angle.

As far as I am aware, this issue has only become apparent over the last few days.

Today's tasks are to check mounts, belts, alternator, compressor,nuts and bolts, get thoroughly annoyed and ask myself vwhy I've got a bloody engine in a blow boat anyway.

[Black Panther 1,591]

Sorry I didn't get back to this last night, I got engrossed in watching a re run of Lassie

 

 

Glad to hear it!!!!

[wheels 543]

A lot depends on just how those engines feed the injector pump.

 

It's a little cam operated Bosch lift pump. I would expect a fuel starvation issue to last more than just a few milli-seconds and also not alter RPM. RPM usually drops for several cycles in this case.

 

Chris, the tip clearance is not an issue. If it did, it would get worse with RPM and it causes a hammering effect through the Hull and at a speed of everytime a tip passes the hull.

If you are stationary, as in pulling back on anchor, it could well be cavitation. Reverse is common for cavitation. the blade is not efficient in that direction and the boat is not moving through the water. My boat cavitates terribly in reverse.

It could be that due to the old box slipping, it may have done so for quite sometime and that has taken the shock out of the cavitation and thus you have not noticed it. Now with a good box, you are.