Trying to fix Volvo Penta 2001 that refuses to start

[Sailing_Beard]

Originally Posted by jimbunyard

Timing.

Forget the marks on the gears, time it based on #1 cylinder TDC compression stroke and figure the cam and injection pump settings from there...

I think this makes most sense, the air intake valve stays open long after BDC and should be shut at BDC, should it not?

It would explain the compression not being able to build more than 140psi.

[nick.theboatman]

Originally Posted by deblen

VP 2000 series "cold start" proceedure maybe? https://forums.sailboatowners.com/th...-start.173628/

Very useful yes - but this relates to use when the cover is on the govenor and the cables are attached (!). We noticed that when you pull the stop knob it pulls a lever that stops the rack moving fully forward or, more to the point, if that lever is not in place the rack moves forward more than usual and more fuel is delivered: = "cold start" mechanism.

In our case we are wiggling (technical term) the rack itself by hand and the stop lever is out of the way.

The thread referred to has an exploded diagram of this lot. The rack (the plate) has 3 slots in it: 2 closed (B), 1 open (A). Slot A takes the pin on the injector, that controls the piston angle and thus the fuel volume per spurt. Slots B take pins (on the ends of externally inserted bolts) that limit the forward-aft movement of the rack. We found that someone had been less than careful in putting the pump back in so that pin A didn't engage in Slot A an this had bent the rack plate (idiot). The plate then didn't slide to the limits defined by Slots B and the throttle never went to 100%.

Moral of the story: watch that pin A engages in Slot A before you go torquing down the pump...

[nick.theboatman]

Originally Posted by Wotname

I'm not being funny but there are only 5 ways that it can leak and you have to double (or triple) check each one.

Agreed....

Originally Posted by Wotname

1. valves

New valves and valve seat polished...
And seating checked by pressurising the pot (admittedly to 100psi) with compressor through the injector port ...

BUT BUT BUT

7. Springs

What about the valve springs? This test pressurised the pot. It didn't rely solely on the springs alone holding the valves shut.
Any ideas...?

Originally Posted by Wotname

2. rings

New rings, honed bore

Originally Posted by Wotname

3. head gasket/head/sleeve interface.

New head gasket, red goo;
New piston;
No evidence of a sleeve actually - you sure this engine has sleeves?

Originally Posted by Wotname

4. badly cracked head (unlikely)

Inspected: no cracks; no puffs of smoke, no bits flying off...

Originally Posted by Wotname

5. injector (very unlikely)

New injector

Originally Posted by Wotname

IIRC, this is a sleeved engine. If so, was the sleeve removed and did the sleeve project evenly above the top of the block when refitted.

Top of bore is flush with top surface of block, no marks on head gasket indicating raised lip.

Originally Posted by Wotname

Or was the compression testing methodology was wrong???

No that was fine - checked against known pressure (in the compressor, relying on reading on compressor pressure gauge); and the gadget we made to take the compression tester gauge we checked with bubbly water and it was sound.

Originally Posted by Wotname

Opps, make that 6.
6. Bent rod; not that this causes leaks but it does lower compression.

Connecting rod or rocker rod? All seem to be in good shape...

So. Next...?

[nick.theboatman]

Originally Posted by Sailing_Beard

I think this makes most sense, the air intake valve stays open long after BDC and should be shut at BDC, should it not?

It would explain the compression not being able to build more than 140psi.

Just a thing.
My manual for my BMC Commodore (4-pot, built 1950 and still popping happily) shows that the input valve closes 30deg ABDC #1 (meaning starting to close at 135, closed at 225). Not a lot happens in the first 45 degrees after BDC and most of the force is exerted between 225 and 315 (when the piston is rising fastest) - just when the valve is fully shut.
Am I missing something here?

[edmundsteele]

A diesel engine needs some fuel air mixture in the cylinder and it needs compression. You don’t have compression and I assume you have done all of the testing for valve timing. For full disclosure, I have never done this with a diesel engine but have used the technique with several large gasoline V8s having a similar rebuild problem. The issue is that the cylinder walls are “dry”. If you squirt a little engine oil into the top of each cylinder, you will get a temporary compression boost. It will smoke like a bugger after it starts but the next time you try and start the engine, the cylinder walls, rings etc. won’t be dry. Once upon a time mechanics used to paint the pistons etc. with STP when reassembling but this is a quick fix. Good luck.
Ed

[Wotname]

Originally Posted by nick.theboatman

.........
No evidence of a sleeve actually - you sure this engine has sleeves?

.............

No, I'm not sure. As previously posted, I'm not familiar with the VP 2001 but I had a vague feeling it was sleeved - however if you haven't removed it, then either it doesn't have one or if it does, the sleeve is still in the same place so it shouldn't be an issue.

[Lou-In-NJ]

Firstly, what model engine do you have?

I concur with an earlier post about your compression being too low. My Volvo MD17C calls for between 284-355psi, when turning at 200rpm; and that's at 17.5:1 compression, which is on the lower side for a diesel, but pretty normal for marine applications.

First check your valve lash, you may not be allowing a couple of your valves to fully seat.
If that doesn't make any difference, it's time to start looking for the source of the compression loss.

If this doesn't work, you should try some pure alcohol in the cylinder and see how long it takes to disappear, and you should do this at BDC, TDC and two more points in-between. You may have a bad hone job, or your rings are not fitting well enough to seal. (and I'm not a fan of the new "ball" style honing tool for anything but a new bore, you are much better off with the traditional three stone honing tool, this tool will help even out waviness of the bore, that the ball style may actually make worse!) By the way, it's typical for an engine's compression to increase as new piston rings seat since they will wear to conform to the bore, but this is presuming a good bore and honing job. Also, if the engine overheated, you could have warped the cylinder liners, and then you're stuck, no amount of honing will fix that.

If your bearings were shot, I'm guessing you had the crankshaft re-ground, so the question here is, did the machine shop de-stroke the engine by using the wrong offset on the throw journals? To test this you need to calculate the volume of the cylinder, including the head, at BDC and divide that by the volume at TDC (the cylinder you can calculate on the back of an envelope, the head volume you'll need to measure with liquid and a graduated cylinder...don't forget to add the head gasket volume!)

But I frankly think the crankshaft throw offset is the least likely issue with compression, you probably should get your valves and seats, ground at a shop; there is a relief angle of usually 0.5 degree between the two surfaces to ensure centering of the valve face in the seat, and lapping worn valves may make the sealing worse; you should lap them after grinding.

I wouldn't bother doing anything until you get the compression up to at least 300 psi; keep all your injectors out when you crank the engine to do the test, until you get a satisfactory result.

Also, you have a problem across the board if you can't get any cylinder to fire, so whatever is wrong, it is wrong in every cylinder. The smoke you see coming out is just high temperature vapor, you're not actually able to burn anything with such low compression.

Don't leave us hanging, post your progress.

[nick.theboatman]

Hi Lou thanks for all this - lots to unpack.

So:

Originally Posted by Lou-In-NJ

Firstly, what model engine do you have?

2001 - 1-pot

Originally Posted by Lou-In-NJ

I concur with an earlier post about your compression being too low. My Volvo MD17C calls for between 284-355psi, when turning at 200rpm; and that's at 17.5:1 compression, which is on the lower side for a diesel, but pretty normal for marine applications.

Completely with that. As I said before: "so where's it going?"...

Originally Posted by Lou-In-NJ

First check your valve lash, you may not be allowing a couple of your valves to fully seat.
If that doesn't make any difference, it's time to start looking for the source of the compression loss.

He re-ground the valves using compound (coarse and fine) and a drill. When I looked with a glass I could see coaxial grooves and shoulders at the edges of the mating surfaces. He bought new valves and then ground them in and also polished a bit with the cerium oxide. But we haven't cut the seats themselves with a seat cutter...

Originally Posted by Lou-In-NJ

If this doesn't work, you should try some pure alcohol in the cylinder and see how long it takes to disappear, and you should do this at BDC, TDC and two more points in-between. You may have a bad hone job, or your rings are not fitting well enough to seal. (and I'm not a fan of the new "ball" style honing tool for anything but a new bore, you are much better off with the traditional three stone honing tool, this tool will help even out waviness of the bore, that the ball style may actually make worse!)

Possible.
Bore could be oval... but it was popping right up to when it decided to not start. New rings...
And it was a "ball" honing tool - issued from Yanmar for their sins; and worked well on revitalising a seized engine before.
I take your point..

Originally Posted by Lou-In-NJ

By the way, it's typical for an engine's compression to increase as new piston rings seat since they will wear to conform to the bore, but this is presuming a good bore and honing job. Also, if the engine overheated, you could have warped the cylinder liners, and then you're stuck, no amount of honing will fix that.

One of the things that stands out is the way that the air was escaping when we put the compressor on through the injector port. It was hissing from the top (a bit) but not the crank case. But this might have been wishful thinking. However pressurising the bore forces the valves shut so looking more like that, maybe.
I feel like I'm chasing ghosts.

Originally Posted by Lou-In-NJ

If your bearings were shot, I'm guessing you had the crankshaft re-ground

Er not exactly (as in "no" - he popped the new shells straight in. Being fair, although the journals were a bit scored they weren't all shot to hell.)

Originally Posted by Lou-In-NJ

so the question here is, did the machine shop de-stroke the engine by using the wrong offset on the throw journals? To test this you need to calculate the volume of the cylinder, including the head, at BDC and divide that by the volume at TDC (the cylinder you can calculate on the back of an envelope, the head volume you'll need to measure with liquid and a graduated cylinder...don't forget to add the head gasket volume!)

So I did have a think about this and got a spreadhseet out... never was any good at thermodynamics - but we seem to be agreed that we have the opposite: while the engine was running without any bearings the piston was lower by approx 2mm. Now that the shells are in, the piston has moved up by 2mm so the compression should be better. So that element looks unlikely.

Originally Posted by Lou-In-NJ

But I frankly think the crankshaft throw offset is the least likely issue with compression

Agreed but very interesting point and certainly worth mentioning.

Originally Posted by Lou-In-NJ

you probably should get your valves and seats, ground at a shop; there is a relief angle of usually 0.5 degree between the two surfaces to ensure centering of the valve face in the seat, and lapping worn valves may make the sealing worse; you should lap them after grinding

This looks like a good step to take.

Originally Posted by Lou-In-NJ

I wouldn't bother doing anything until you get the compression up to at least 300 psi; keep all your injectors out when you crank the engine to do the test, until you get a satisfactory result.

(only 1 pot so we don't get that luxury)
300 might be a bit optimistic - but 270 agreed.
The point is that it is a big jump from 140 to 270
This seems to be the central issue so thanks for your thought.

Originally Posted by Lou-In-NJ

Also, you have a problem across the board if you can't get any cylinder to fire, so whatever is wrong, it is wrong in every cylinder. The smoke you see coming out is just high temperature vapor, you're not actually able to burn anything with such low compression.

(1-pot) yup we also tried a blow-torch on the exhaust and it did burn.
We also tried lots of other nefarious things that I couldn't possibly mention
By the way where can you replace a melted-crashed-and-burned hot-air gun...?
(note to self DON'T spray in the Easy Start at the same time as the hot air blower is on..)

Originally Posted by Lou-In-NJ

[B]Don't leave us hanging, post your progress.[/B

Of course we will - very grateful for everyones comments and thoughts.

I've been working on diesels in various shapes and sizes for over 20 years and I've never known one like this little darling.

[Hesti]

The piston does go right up to the top of the cylinder, doesn't it? I've had that ages ago on a small motorbike, that at some time, they had changed connecting rod length and also the position of the eye in the piston in the design. A short rod with a piston that had its eye nearer to the top didn't give enough compression.


The valve timing thing sounds like it is worth investigating further. If the intake valve does not open at all, you would also see not enough pressure when spinning the engine with the starter motor.



The "some oil into the cylinder" (something like a teaspoon full) is always worth trying.


Some engines have decrompession levers on the head to support hand starting. That might also be something to check on your engine.

[Lou-In-NJ]

Originally Posted by Sailing_Beard

I think this makes most sense, the air intake valve stays open long after BDC and should be shut at BDC, should it not?

It would explain the compression not being able to build more than 140psi.

Yes, with the operating rpm of a diesel, there is little "volumetric efficiency" to be gained by allowing the intake valve to be open after BDC, I'd say double check your timing marks, and don't rule out the idea that you may be looking at an erroneously marked gear. Search online for a picture of that part and see if the keyway and timing mark match what you see on your engine. If you do the trigonometry, you might find that if the intake valve closes 23 degrees late, that only gets you about 10:1 compression, and that might be the entire issue.

[BlueH2Obound]

Timing has been mentioned several times, not going by the marks, but from TDC, compression stoke. I have come across engines that had gears with incorrect timing marks, marks that fit another engine on them. When rebuilding, I generally verified marks by finding TDC compression stroke, then using inclinometer on the crankshaft to verify degrees of rotation for firing. IIRC, I've found probably 2 or 3 engines who's timing marks have been off. Caused a WORLD of heartache and frustration until the problem was identified!
Although an aircraft engine, and gas (same principles apply), the best one was I came across was a Lycoming IO360 that customer purchased as a Factory Re-manufactured engine. Aircraft wouldn't climb worth a damn, and lacked take-off power after engine replacement. Tried EVERYTHING, then finally used a degree indicator on the nose cone and discovered that the timing marks on the ring gear were 12 degrees off of specs . . . Engine company ended up paying for all labor charges, and sent parts to correct the error . . .


TIMING!

[Lou-In-NJ]

I forgot the basic leak-down test. Test each cylinder for how long it will hold 140psi; crank the engine by hand and stop at TDC. I'd say less than 15psi per second (for the first 2 seconds) would be at the limit of acceptability; any more, then you have a sealing issue.
Check this out too:
https://www.youtube.com/watch?time_c...ature=emb_logo

[jimbunyard]

Originally Posted by nick.theboatman

Yes did that - in terms of drew up a timing diagram.
Remember that this is a 1-pot engine...
Exhaust valve is closing from 630 deg to 0 deg; opens from 510 to 585; stays open between 585 and 630;
Inlet valve opens from 0 to 90, stays open 90 to 135, closes between 135 and 225 (spec says 30deg > BDC #1);
Injection cam starts rising at approx 260, peaks at 380 and is back down by 450; manual says injection at 22 +/- 1 BTDC (#2) (ie 338). We are squirting at 338.

I realize this is a pretty obnoxious question, but are you spinning the engine in the correct direction when you're making these observations?

[Scubaseas]

Its been apart don to the crankshaft, and back, 5 times now in the past 3 weeks
reassembled including trying 4 degrees advance on the crank-cam angle (note that when the 2 dimples on the cam line up with the one on the crank this gives 5 degrees after TDC);
straightened damaged and bent rack;
re-set the injector pump shims to correct height assuming 22 degrees BTDC injection point;
lots of new gaskets;
compression test but shows only 140psi

It sounds like a cam timing issue.



You need 275 psi to 400 psi compression to run a diesel.


How are you able to change the valve timing? There are keys and keyways in both the crank and cam shafts, yes? You should be in the 2 on cam one on crank teeth.

[DougR]

It’s never gonna run on 140 psi compression pressure. Standard spec for this engine is 20-25 Kp/cm2, which is 285-355 psi, and you are less than half of the minimum. New valves, rings, etc. should be over 300 psi easy.

If it’s an early version engine with the valve decompressor, remove the decompression lever, pull off the valve cover and make sure the de-compression shaft is correctly positioned and not holding the exhaust valve open a bit. Then recheck the valve clearances.

If that’s not it then follow all the leak down stuff previously mentioned.

Also, if you are timing the injection with a Wilber tube, or similar, be sure you don’t time it with the pump in the cold start position. The cold start position increases fuel flow but also retards it about 8 degrees.