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Author Topic: New pistons Petter PJ2, block after short time engine running. Clearance?  (Read 2642 times)

Rob PetterPJ2

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Hi, I'm Rob from Amsterdam, NL, new to any forum.
English is not my native language, and with the technical stuff I have to look up the english words and I may not understand everything you may try to tell me, right away, but let's give it a try.

I had no experience working on a diesel engine before 4 years ago, but I do have a technical insight. I learn while doing, and I ask a lot and read a lot, especially now that there have been and are serious problems with this old machine. I'm used to open every household thing that's broken and try fix it, and mostly I can. But I know I'm still very much a beginner with diesel engines, compared to the advanced hobbyist mechanics.

I wish I had a manual for exactly this engine Petter PJ2, 22 HP air cooled. Motor nr 13724, put in a Harding life boat in 1972.
When, after a few years the engine started to show problems (smoke, overheating) small pieces of one piston appeared to have broken off, I had an engine revision workshop find me 2 new pistons (they got them from the Lister-Petter company) and have the cylinders honed by them.
Now that I've put the engine back together, and both cylinders firing, after little time (2 minutes various speeds, 10 minutes slow speed) the engine slows down, and when I turn it off, the flywheel can't be turned for a short while, and after that only with force. When the engine cooled down, it all turns easier, as normally. I guess it's a result of the pistons expanding by the heat and then get stuck in the cylinders. The oil in the carter is Shell Rimula R4 Multigrade 10W30.
A manual of a similar engine says, with new pistons one must indeed let the engine run first for just 2 minutes, without any load, then 10 minutes let it do some work, and then longer and longer before really having it run for a normal, longer trip. What worries me, is that the first two times the engine stopped after 2 minutes, for blocking itself. The third time after about 10 minutes running slow. The pistons, or at least one, gets stuck and the flywheel can't be turned for a minute or two.
How normal or abnormal is this? To me it doesn't 'feel' good, that the pistons get stuck.
Both cylinders seem to warm up normal, and develop an equal temperature.

1. Should I be worried about the piston clearance being too little?
2. What else could cause this rapid blocking, that seems so related to the heating up?
3. Who could provide a manual for exactly this engine?

I'll of course be happy to hear some responses

glort

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Your english is excelent so do not worry about that.  By " Blocking" I take it you mean  Siezing.  That is when the engine locks up and  won't turn because the parts tighten up on each other.

There is no way the engine should Sieze because the pistons heated up and swelled. The clearances are way too tight. The only way this could fix itself is to wear either the pistons or the bore or both so there is adequate clearance and neither is at all a good thing.  You will get the sides of the piston scrubbing and smearing and possibly breaking again as before. The place that did the job botched it.  Most times bores are  honed out then Finally finished to suit the pistons.  Maybe they missed the last step and only bored the block to the piston size not allowing for final finishing and clearances.

The engine needs to be torn down again and the clearances Checked and corrected. Make sure someone competent also check the barrels are round and Square to the block. I would also be checking oil pressure just in case it's not the pistons but the bearings. Unlikely but there is defiantly a substantial problem somewhere.

If the engine was overheating before rebuild, was this checked for blockages in the water jackets and passageways? If not you may be getting localized heating which is causing the Piston to Seize.
In any case, the engine needs to be pulled down again and these things Checked because engines should NOT sieze while running and the engine is doing a LOT of damage to itself by doing this.

ajaffa1

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Hey Rob, I agree with every piece of advice from Glort, however he missed one thing(not like him), I would be looking at the piston ring gap. Piston rings grow as they get hot, if the gap between the two ends is too small the engine will seize after about five to ten minutes. Very easy to fix: remove the piston rings and place them in the cylinder, use the bare piston to push them down the cylinder so they are square to the bore. Use a set of feeler gauges to measure the piston ring gap at the top and bottom of the bore. If the gap is too small, file or grind the end of the ring until they are within specification. Do this for every piston ring and then reassemble. The problem should be solved.

Your English is very good, good luck, let us know how it goes,

Bob

glort

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Hey Rob, I agree with every piece of advice from Glort, however he missed one thing(not like him), I would be looking at the piston ring gap.

Didn't Miss it, never even occurred!

Good pickup Bob!
With a bit of luck, it might be that simple and easy to fix.

When I used to do hi performance 2 Strokes, I used to like to use " filebacks" for rings. These were oversize rings that you Filed the gap back to that you wanted. You could get real trick and file the ends back at an angle so they over lapped and gave even better sealing.  Never had a problem with them heating up and sticking, maybe I put more clearance than I realised. :0(

I marvel at modern engines with just one tiny thin ring even on 4 Strokes.  Probably explains why they only last 20 hours and you have to replace the rings.

ajaffa1

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Hey Glort, used to do similar stuff with Cord over sized rings in the UK, my thing at the time was Mini Cooper engines. Had a few seize after a few minutes because we went too tight on the rings. Had a lot of fun with those simple engines, miss the reliability, simplicity and cheap parts.

Bob

Rob PetterPJ2

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I SEE NOW, THERE ARE MORE RESPONSES. I'LL ANSWER THEM RIGHT AWAY.

Thanks, Glort, for your quick reply.
Ha, you meant seizing, instead of siezing. Yes, it gets jammed.

Cooling.
There's no water cooling. It's air cooled. I'll attach a movie of an identical engine, that I found online.
https://www.youtube.com/watch?v=TxLd4O31AMY

As also that movie shows, after just two minutes of running stationary, no such engine will get jammed for overheating, even if the air cooling system isn't attached, as was also the case when I had my test runs. Do you agree, or am I mistaken? Before it was never a problem.
After two minutes running I could still touch the cylinder fans, without getting burned. But the engine was slowing down and getting jammed.

Oil supply pipe. Seems OK.
Oil does flow to the rockers of the valves. When I turned the flywheel by hand (feet, actually), and the oil supply pipe not yet attached to the cylinder heads, I saw oil was coming out at the top side of the pipe.

Oil between cylinder and piston. Seems OK.
When I had already taken the cylinder heads off, after the second jamming, to check if there was any visible damage, and then turned the flywheel by hand, I saw the cylinder wall got oil.
I'm not sure where the cylinder gets the oil from, by the way. Does it come, partly, from the oil of the valve rockers through the valve of the air inlet, or does it just splash up, from the carter, against the bottom side of the pistons and cylinder, as I read somewhere?

New pistons, slightly different from old ones.
The new pistons have fewer of those little holes for the oil to go through. The engine workshop guy says these holes are to drain off the oil, while I thought they're meant bring the oil to the cylinder wall, after it splashed up against the bottom of the pistons.
In any case, turned by hand, the pistons and cylinder wall show to get oiled.

Oil pressure. Don't know (yet)
I don't have a meter for that. But I know the oil is supplied to the valve rockers.

Bearings getting oil?.
The bearings of the pistons at the crankshaft, right?
Hm, I hope I never have to get in there, that far. Do they get oil through the crankshaft itself, or from oil splashing up? I don't have a manual of this particular engine.

"check the barrels are round and square to the block"
You mean the cylinders, right?

Barrels square to the block.
What could cause them not being attached square to the block?
When I bolted the cylinders back on the block, 6 nuts per cylinder, I took care of bolting nut 1 and 4, then 2 and 5, then 3 and 6, building up the force used in 4 phases.
But maybe the gaskets that are placed under the cylinder make one cylinder tilt a tiny bitty?
Somehow, one of the pistons doesn't reach the same height as the other one, and therefor, to get even compression, one cylinder gets a stack of gaskets under it, and the other one just one, a fraction of a millimeter thick.
Maybe that stack of 5 super thin gaskets causes a problem? Maybe some dirty under it, that I overlooked, makes a barrel tilt a tiny bit? Because tilting is what you mean, not?
What had surprised me, is that one of the (identical!) pistons didn't reach the same height to the cylinder head. What could be the cause? And earlier fixing of a problem that was before my time? Anyway, I decided the bump clearance should be equal, and therefor I took some gaskets away there and put them under the other barrel. The bump clearance is about 1 mm, now, as seems ideal for an almost similar Petter. When turned, the cylinders seem to have equal compression (very hard to get over it, pushing the flywheel with the feet) and when the engine is started, the seem to do fine, both cylinders fire and the cylinders get equally hot (felt by hand).

So, when I take the engine apart again, I'll check these gaskets and if anything would be there that make a barrel tilt.

Check the barrels are round.
OK, I will find a way to do that.

Piston clearance.
The manual of an almost similar Lister-engine "type LD" says the clearance should be no less than 0.005", being 0.127mm. BUt this is what I need  the right manual for...
Now I wonder, what did the guys of the workshop use as reference, then? I know they don't have that manual either. They surely didn't know what the bump clearance of this particular engine should be.
The new pistons definitely had a lesser clearance than the old ones, but I found that logical, for the old ones, and the barrels had been worn out.
But when I was putting the honed barrels back over the pistons, I was already worried about one not going in so well. Both of the pistons would lift the heavy cylinders up along their long bolts, when I turned the flywheel. No sliding. With oil, no sliding either. When I told the workshop guys about one piston needing more force, they said it was not unusual. Which I found strange, because it shows a difference that you don't want there to be, right? But they're the professionals, and they sometimes shake their heads when I talk with them, obviously not knowing the right terminology, the right names of the engine parts (I earlier had them check the fuel injectors, when I started with bringing this engine back to life 4 years ago, by cleaning the pipes).

When you say, the engine revision workshop guys may have 'botched' it, it is the first thing that came into my mind, when I was putting the engine back together and one piston clearance seeming so cramped.

Oil scraper ring. One more problematic.
One of the pistons went back in the barrel with more difficulty, especially for the scraper ring at the bottom. That needed some work to get it in. Different from the other piston. A second time that I took it all apart and back together, same thing happened.
Could that cause this engine getting jammed after a few minutes idle running?

Clearance again
I'll go confront the workshop with the clearance problem, again, then and ask them what measure they applied.

Glort, I'll be happy with some more of your thoughts about it all.

Cheers
Rob

ajaffa1

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Hey Rob, every symptom you have posted suggests that the piston rings do not have sufficient gap. It`s an easy fix but takes a little time. Much better an engine that is a little tight than one that is too loose before it`s done any work.

Bob

Rob PetterPJ2

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[quote author=ajaffa1
"If the gap is too small, file or grind the end of the ring until they are within specification. Do this for every piston ring and then reassemble. The problem should be solved."

Hi Bob,
oh, that'd be great, if that would be all. As I wrote as a reply to Glort, one scraper ring seems to be problematic, and also the second time I worked it into the cylinder.
These rings came with the pistons from Lister-Petter. Could they put the wrong rings on it, then? But how do I know "If the gap is too small"? I haven't found the manual for this thing yet. Is there a way to calculate it?

Anyway, I'm happy to hear that such a small thing could indeed jam that robust engine.
So, I happy to have found some guys at this forum who are really helping, and not speak technical 'chinese' to me leaving me puzzled about what the h*** they mean.

One of the bolts connecting the oil supply pipe to the cylinder head (to the valve rockers) appears to be a wrong one, slightly off size, too short, wrong thread, and when I bolted it back in, not yet knowing that, it decided to end it's working life (the thread got too damaged), so I need to find me one of have it made, before I can start the engine again. That will be somewhere next week I hope.

Glort and Bob, thanks!
« Last Edit: October 18, 2018, 01:09:21 PM by Rob PetterPJ2 »

ajaffa1

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Hi Rob, there is sure to be a formula for working out what the correct gap should be, sadly I don`t know what that is. If you post the diameter of your pistons I am sure that someone like Dieselgman or 38ac will give you that information.

I am also a little concerned that you don`t have the same bump clearance on both cylinders, please check out how to set this correctly on the WOK at the top of the home page, courtesy of 38ac.

Bob

glort

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I don't see anything " Normal" about the pistons fitting the bores different.  They should all be the same size so why would one be noticeably Different to the Other?

When You pull the engine down I would take the rings off and see how the pistons fit and measure the clearance.  There may be a tolerance difference but not so much that one piston actually Binds.

As for lifting the Cylinders when Fitting the pistons, yes, that is not unusual but if it did it without the rings fitted, I'd be very wary of that.
The difference in piston height in the bores I also think is a concern.  Could be a bunch of things,  Deck heights not right, uneven piston heights, different rod lengths.... Again none of these things good or what you want.

You have a difficulty here in it seems you assembled the engine and the workshop did the machining. I would expect if they did the lot they would have checked things like ring gap and  piston heights and corrected them properly.
You don't need a manual for everything. Many things on engines are roughly the same and close enough is good enough and you know when something is not right.  For an engine that size, any Engine, I certainly wouldn't want a piston tighter than 5 thou and that sounds pretty tight to me.  On the skirt I'd be thinking at least 10 thou or more.  For the ring gap, it varies with which ring generally but something around 10 thou would be common.  It does depend on the ring type as well.

I doubt the oil ring would be causing the problem unless it has no gap because that shouldn't get very hot like the compression rings and expand that much but then again, if it has no gap....  Unfortunately this is all stuff that should have been checked as the engine was re assembled.
The holes in the piston should not be critical. The rings are generaly scrapers so are in fact drain holes.
One thing I always do on engines I assemble is to put a 2mm chamfer on the piston bottom edge. This allows the piston to ride up on the oil film and get between the piston and the bore instead of the lip scraping the oil away and there being no oil film between the 2.  The oil rings are to control the oil film so you do not want the piston skirt taking it all away before hand.

If the thing has been seizing  repeatedly, The bore may now be scuffed or scratched.  I'd be giving it a Close look over and probably running a hone through them  anyway just to make sure there are no high points now. If the ring gaps are too tight, you can almost guarantee they will have dug in and put scratches in the bore.  The gap is where the rings will try to push out the most and have the sharpest corners.  Something I always file a bevel on as well so the ends won't scratch if they are not pinned and can come round the thrust side of the engine.   Depends how deep any scratches are but if they are bad enough, the proper practice would be to go back to the start and hone the bores again and put in oversize pistons and rings.
  Again, depends on what you find and how critical a duty the engine has to do. You can get away with a lot if the engine is more for play but if it's going to do work you need to rely on, at best you will have an engine that probably goes through a bit of oil.

Depending what you find, it may be worth having the engine re assembled by the engine shop so they can check and set all these things.  If they don't do a lot of diesels, I'd be taking it to one that does because they will probably have a good idea off the top of their heads what the numbers should be in the ballpark of.  They don't vary all that much from similar engine to another.

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #10 on: October 18, 2018, 02:22:09 PM »
I am also a little concerned that you don`t have the same bump clearance on both cylinders, please check out how to set this correctly on the WOK at the top of the home page, courtesy of 38ac.

Hi Bob, but I wrote I had adjusted the bump clearances. They are the same now by putting more gaskets under one cylinder. I did that after I saw that one piston didn't reach as high as the other one. Somewhere further down there must be something that creates a 1 mm difference. This engine has been worked on before I got it. It shows at various spots.
Cheers
Rob

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #11 on: October 18, 2018, 02:25:55 PM »
Hi Rob, there is sure to be a formula for working out what the correct gap should be, sadly I don`t know what that is. If you post the diameter of your pistons I am sure that someone like Dieselgman or 38ac will give you that information.

Diameter of pistons: 99.6mm = 3.9212598425"
I've contacted dieselgman.

Thanks
Rob
« Last Edit: October 18, 2018, 02:48:12 PM by Rob PetterPJ2 »

ajaffa1

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #12 on: October 18, 2018, 11:52:37 PM »
Hey Rob, When you fitted the new pistons did you fit new small end bushes (wrist pin bushes in the USA)? generally these are made of bronze and are pressed into place. They require reaming afterwards. If the machine shop reamed these out of square the piston will bind at the top one side and at the bottom on the other. When you checked the bump stop did you use two identical length pieces of lead, one either side of the piston above the gudgeon pin. The two pieces should measure the same thickness after performing the bump. If they do not then the bush is out of square.

Bob

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #13 on: October 19, 2018, 01:31:29 AM »

Hi Bob, but I wrote I had adjusted the bump clearances. They are the same now by putting more gaskets under one cylinder.

You shouldn't have to do that, it is really bit of a band aid solution.  Packing anything with multiple gaskets where there is not meant to be to take up dodgy tolerances is never a good practice. All the heights should have been checked as things went along.  The cylinders for instance should have been checked they were the same height and machined if they were not. I would hope the machine shop did that but they might have done as asked and nothing more and if not asked in the first place..... same as the pistons, rods  and normally the crank throw out would be as well. Bob found his bearings were out when he did his engine. It starts at the beginning and goes from there.

I think this is a concern that the engine has been put together without these basic and fundamental things done.
Unfortunately you can't ever assume things fit together right because they are new or refurbished.  There are tolerances for a start. Everything has a margin of this to that rather than one specific. If it is within the range then it's good. The thing is on occasion, all the margins go to one side instead of balancing.  If the bore is tight and the pistons are large and the ring s are a fraction oversize..... it all adds up to a tight engine that could cause problems you are seeing.  you really need to pull it all down and check everything to see where the problem lies.

It could be none of the things we have suggested. It's not easy to diagnose things when you can't see them and only relying on the info you are given. Possibly one look at the engine would make the problem obvious, maybe not but there is nothing like seeing and playing with something yourself same as not actually being able to see what the engine does when it stops.

I have often found the shortcut to problems is doing things the long way.  There is every possibility you may have more than one problem so pulling the engine apart and starting from scratch may in fact be the quickest and easiest fix.  Start with you bump Clearance and find why that's different.  are the Cylinders 1mm different? if so then you can get that fixed. maybe the pistons are different heights in the crown, are the clearances OK or is one far too tight? What ARE the ring gaps, is the bore still OK or does it need re machining now?..... so it goes.  If the cylinder heights are out and the Ring gaps too tight then you have fixed both things.

Also, if you don't have a manual, how did you determine and what did you set the rocker clearances at?  Won't have any effect on the problem but it's a measurement that needs to be set for best performance.  10-12 Thou would be ballpark on these too but just wondering how they were set and where the number came from?


38ac

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #14 on: October 19, 2018, 03:18:18 AM »
The bump clearance on a PJ is indeed set via the number of and various thickness of the base gaskets which are actually steel shims. As I remember three different thickness are available to be used in combination as needed. That being said 1mm is a LOT or variance. Much more than,would be seen normally and can be due to issues that are not readily apparent. From what I have read on this thread you need to put down the tools until you have a manual. A person can feel his way through a simple overhaul but when an engine has suffered previously in unknown ways all that can be accomplished by me from a distance is to throw darts at it. One possibility that will not be in a manual is that the shop that honed your cylinders did not use a fixture that simulates being installed on an engine. The bores are pulled around by the clamping forces thus A cylinder that is made round while not clamped will not be round when installed.
« Last Edit: October 19, 2018, 11:01:15 AM by 38ac »
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