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Author Topic: New pistons Petter PJ2, block after short time engine running. Clearance?  (Read 14844 times)

ajaffa1

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #30 on: October 24, 2018, 10:41:33 PM »
Hey Rob, honing tools come in different sizes for different size bores. Look on fleabay for one that will adjust to at least four inch. They also generally come with different abrasive heads, coarse, medium and fine.

Bob

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #31 on: October 25, 2018, 09:07:31 PM »
Hey Rob, honing tools come in different sizes for different size bores. Look on fleabay for one that will adjust to at least four inch. They also generally come with different abrasive heads, coarse, medium and fine.

Bob


Hi Bob, today I mail-ordered the proper honing tool with the proper 'sanding stones', honing oil, a piston ring opener, a 'tension wrench' that can handle the in the manual described force for the cylinder head bolts, and some more delicacies from the tool candy shop.
Before all that arrives, there's plenty to do: draining the oil from the block and cleaning it, cutting new gaskets, checking the shims or making a new one with the desired thickness.
And when Jim Perkin's package arrives with the manual, operation handbook, oil banjo bolts (one put in my engine wasn't properly fitting!) and two piston + .020 oil rings, I bet I'm going to have an interesting week after this weekend!

Here's the monster in the state I got it in, in 2011 (here without air cooling cover). It took me three years before I dared touch it. But all it needed for its first start was cleaning the fuel pipes (and a scooter engine to get the flywheel turning with enough speed).
« Last Edit: October 25, 2018, 09:23:40 PM by Rob PetterPJ2 »

Matt12

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #32 on: October 26, 2018, 01:41:24 AM »
Hi Rob,
            I'm a newby to this forum but am an ex motor mechanic, (retired).
Did you notice any scars on the piston skirts, assuming they are alloy pistons, if so, the pistons are 'grabbing' the bores, due to insufficient clearance, if not, then it's likely the top rings are too tight, ( too little end gap), this gap should in your case be around 4 thou per inch of bore, 4x4 = 16 thou.
Hope you have a successful outcome.

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #33 on: October 26, 2018, 12:01:39 PM »
Hi Rob,
            I'm a newby to this forum but am an ex motor mechanic, (retired).
Did you notice any scars on the piston skirts, assuming they are alloy pistons, if so, the pistons are 'grabbing' the bores, due to insufficient clearance, if not, then it's likely the top rings are too tight, ( too little end gap), this gap should in your case be around 4 thou per inch of bore, 4x4 = 16 thou.
Hope you have a successful outcome.

Hi Matt,
thanks for the extra info. I'll check for scars at the pistons, today. But the 16 thou may not be correct, at least not for this particular engine, as earlier written by dieselgman. According to his data is has to be like double that distance. The Petter engine collector Jim Perkins says the same. He'll snail-mail me the manual today.
When pushed the rings into the cylinder for about 2 inches, the gap is only 0.3 mm, which is 0.118 inch. According to the proper manual for this engine (PetterPJ2) it should be 3 times that.
« Last Edit: October 26, 2018, 12:12:28 PM by Rob PetterPJ2 »

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #34 on: October 26, 2018, 02:31:49 PM »

Have you got both cylinders off and checked the gaps of both lots of rings yet?

If so what were the gaps on each one with each ring?  Did you measure piston Clearance.

Hi Glort
yes but I'd already written so. at the top pf the cylinder the ring gaps are 0.4 mm. But 2 inch lower the gaps are just 0.3 mm (0.118 inch). All rings the same.

The piston clearance is around 0.3 mm (piston, when I had it lowered in cylinder, pushed to one side, feeler gauge at other side).
« Last Edit: October 27, 2018, 02:03:12 AM by Rob PetterPJ2 »

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #35 on: October 26, 2018, 03:46:47 PM »
You can't be that helpless, Glort! I have to do it all the time, go from mm to silly inches...
Here's a tool
https://www.rapidtables.com/convert/length/mm-to-inch.html

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #36 on: October 27, 2018, 05:22:26 PM »
Hi Rob,
            I'm a newby to this forum but am an ex motor mechanic, (retired).
Did you notice any scars on the piston skirts, assuming they are alloy pistons, if so, the pistons are 'grabbing' the bores, due to insufficient clearance, if not, then it's likely the top rings are too tight, ( too little end gap), this gap should in your case be around 4 thou per inch of bore, 4x4 = 16 thou.
Hope you have a successful outcome.

Hi Matt,
i can't believe I hadn't noticed it yet, but indeed, one piston is clearly damaged in four places at its skirt. The other one a tiny little bit, but hardly.

So, then I thought, is it the cylinder, or is it the piston? I measured the clearances, at the top.
Piston 1 had 0.3 mm, piston 2 had 0.4 mm clearance.
Then I had the cylinders change place.
Piston 1 had 0.3 mm (0.0118"), piston 2 had 0.4 mm (.0157") clearance....
Meaning: the pistons aren't exactly of the same size, right? Not at the top, at least.

In inches, the measured difference between the pistons' diameters would be 0.0039".

Your suggestion and Glort's very first response (and my own in my 'opening speech', but that more due to not being hindered by any other knowledge) that the clearance between pistons and cylinder might not be enough, seems to be correct.
That fits to the picture of the damage.

Two inches down from the top, the clearance is about 75% of that at the very top of the cylinder, I noticed when I measured the ring gaps at the top (0.4 mm) of the cylinder, and further down (0,3 mm).

I'm not happy with these traces at the piston skirt, can you imagine...
I have to wait for the manual Jim Perkins sends me to see what the clearance should be.

« Last Edit: October 27, 2018, 06:29:19 PM by Rob PetterPJ2 »

mikenash

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #37 on: October 27, 2018, 08:15:26 PM »
Rob - quite a long way back in this thread you said that you had been supplied with oversized pistons because the cylinders had been honed.  When I read that I assumed you meant the cylinders had been bored to an oversize and you were just speaking casually. 

But, reading your comment re the piston skirts, I wonder if the cylinder has been bored correctly to suit the oversize pistons.  Do you know?

Just checking . . .

Cheers, Mike

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #38 on: October 27, 2018, 11:42:06 PM »
Rob - quite a long way back in this thread you said that you had been supplied with oversized pistons because the cylinders had been honed.  When I read that I assumed you meant the cylinders had been bored to an oversize and you were just speaking casually. 
But, reading your comment re the piston skirts, I wonder if the cylinder has been bored correctly to suit the oversize pistons.  Do you know?
Just checking . . .
Cheers, Mike

Hi Mike,
I had brought the engine revision shop the old piston that had little pieces broken off, and the two, scratched cylinders, and had them do what they had suggested: find a supplier of new, slightly wider pistons for this particular engine (given the type, model and engine number) and hone the cylinders accordingly.

When I later picked up the new pistons and honed cylinders, how could I expect the clearance then to be not OK? It was their suggestion to do it like that, and their job to do that right, wasn't?

I don't think I did anything wrong, with the reassembly, or it was that it didn't come up in my mind, that I should find a way to check if they'd done the job right.
I think... but correct me when I'm wrong.

« Last Edit: October 27, 2018, 11:54:10 PM by Rob PetterPJ2 »

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #39 on: October 28, 2018, 12:30:55 PM »
Yes, the engine re conditioners should have made sure the clearances were right and this is why YOU need to check them.  In the end, the responsibility ALWAYS lies with the guy assembling  the engine not the guy that supplied the parts. Anything wrong should be picked up during the build.

ASSEMBLY GUY's FAULT...
Dang, that's what I once told a publisher who had the emailed LOW RESolution example of my illustration printed on a book cover, instead of the high res, sent on a CD together with the typography and the design. 2000 books were printed with low res cover, not showing the fine details I'd put in. I said the production leader screwed up, for not noticing the mistake, that those who assembled it, had made. So, I get the point you make.

But still, what were the honing guys thinking?
When the engine seized after the first two tests, I wrote them an email about it, asking them what could have made the engine seize. All they replied with was: "A pity it didn't work out as we'd planned".

OVAL shaped PISTONS, or not?
I've also been measuring and measuring, over and over again, both the old pistons and if there's a difference between the longer and the shorter diameter of the oval, it's not more than 0.05 mm, which is 0.00197 inch, roughly 0.002".
The Lister LD manual I have doesn't say anything about the oval shape, when measuring the piston clearance doing maintenance. It just says: "measure it, it should be not less than this".
Could it be, that with these old engines, the oval shape wasn't yet invented, or that it isn't applied for every engine? Or is the 0.00197 inch difference in length and width of the oval shape about the expected margin?

DAMAGE TO PISTON
Here's a picture of the damage to Piston 1. It has similar damage at the opposite side. The grooves rubbed off, here.
Piston 2 has tiny traces of damage. The grooves still there, and all around.
« Last Edit: October 28, 2018, 03:09:15 PM by Rob PetterPJ2 »

ajaffa1

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #40 on: October 28, 2018, 10:15:03 PM »
Hey Rob, pistons should be round and the sides should be parallel. The cylinder bores should also be round and the the same size all the way up the bore. The manual should tell you what the correct clearance between the piston and the cylinder should be. Some pistons have a mark on them indicating which way they are to be fitted, this is usually because the gudgeon pin (wrist pin) is slightly offset in the piston.

The wear on the piston in the photograph suggests that the piston is not round and that the clearance with the cylinder wall is too small. Alternatively the cylinder walls are not parallel. Take them back to the shop that did the work and shout at them until they put it right.

Bob

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #41 on: October 29, 2018, 11:52:50 AM »
Hey Rob, pistons should be round and the sides should be parallel. The cylinder bores should also be round and the the same size all the way up the bore. The manual should tell you what the correct clearance between the piston and the cylinder should be. Some pistons have a mark on them indicating which way they are to be fitted, this is usually because the gudgeon pin (wrist pin) is slightly offset in the piston.

The wear on the piston in the photograph suggests that the piston is not round and that the clearance with the cylinder wall is too small. Alternatively the cylinder walls are not parallel. Take them back to the shop that did the work and shout at them until they put it right.

Bob

Hi Bob
you might encounter a dispute with the other guys here about the possible oval and parallel shape of pistons in general. I've read there are even barrel shaped pistons, and the oval shape would be normal when the piston is cold. It would get round when heating up. It's all about fractions of mm. When I measure the old pistons, the difference in length and with of the oval would be no more than 0.05 mm (roughly 0.002"), as written earlier.
The Lister LD manual, of a 1 cylinder engine, does mention the  direction of the pistons and says it would show the right positioning by the word "Camshaftside" on it.
My old-, nor the new pistons mention any such thing and do not show a mark, or sign. It only shows a number.
When I look into the bottom side of one of the old pistons, I see a tiny desaxation. It could be as little as the thickness of a penny, or even half of that. It goes to the side of where also the number is written at the piston's top.
I understand the function the desaxation (now that I've read about it).
I may have put the new pistons in wrong, both of them with the number at the other side. But could that have resulted in seizing after two minutes running stationairy without load?

I'm waiting for the better manual to be dropped in my mailbox, that's being sent by Jim Perkins from the UK.
It's a pity he had to tell me its a manual of a slighty different model, still... hm. I'll know how 'slightly' when I have it in my hands and see the illustrations.

I wait for that, study the book, before I dare go back to the engine renovation garage to show them what happened. I bought the honing tool and oil, but if honing needs to be done, I may still have them do it.

And yes, I will consult an expert, Matt!

There's one more unusual thing, with this engine: one injector has 4 spraying holes, the other one only three. This was discovered when I had them tested. For the rest, they're identical.
« Last Edit: October 29, 2018, 01:16:47 PM by Rob PetterPJ2 »

sirpedrosa

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #42 on: October 29, 2018, 04:31:42 PM »
Hey Rob

Cheer up!

Unmount everything until the last piece, rebore cylinder to next oversize (or get new standards), fit new pistons (send damaged ones to recycle to get some pennies to help buying new ones).

I'll get there, with more acurate patience, and more burned eyelashes.

Think of the new pistons as less of a headache pill you did not spend at the pharmacy.

Don't forget its your boat engine, it must be reliable.

Thumbs up!
BR
VP
By order of firing up:
Bernard 18A - 1968 (mama's water pump - year of my birth)
Petter PAZ1 - Jun 1967, 3HP, sn 416xxxx
Petter PAZ1 - Nov 1979, 3HP, sn 425xxxx
Lister 12/2 - 12651227, the pearl!

guest23837

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #43 on: October 29, 2018, 05:41:19 PM »
Holding back again Glort! You should say what you think

mikenash

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #44 on: October 29, 2018, 05:47:58 PM »
Holding back again Glort! You should say what you think

Yes.  Man turns to the forum for some advice and support and gets this.  Dickhead