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Author Topic: New pistons Petter PJ2, block after short time engine running. Clearance?  (Read 1386 times)

ajaffa1

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #90 on: November 01, 2018, 09:15:17 AM »
Hey Rob, when I read your earlier posts I assumed that a re-bore was what you had done. The way this works is: you measure the wear in the bore. Oversize pistons generally come in increments of +.010 inches. If the wear is less than .010 inch you re-bore to allow for a +.010 piston. The cylinder is then honed to provide a key for the new piston rings and very small groves/indents for the oil to sit in to lubricate the new piston rings.

If what your engineers have done is to hone a cylinder out without a re-bore and then try to fit an over sized piston they should be shot for criminal incompetence.

Very sorry to hear the Dutch government have joined in with the all pervasive green stupidity. Could you find a mooring outside of Amsterdam, so you can continue you passion without being robbed by the taxman?

Bob

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #91 on: November 01, 2018, 09:17:11 AM »
I thought you fitted over-size pistons and rings? 5 or 10 thou is a lot of metal to hone off if the pistons are oversize.

It's a HUGE amount to do with a hone. And..... you would NEVER be able to keep the barrels straight and true with an engine hone no matter if you set it up in a drill press or whatever. They would be wide in the middle and narrow at the ends guaranteed.  Definitely needs to be done on the proper machine by an expert.

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #92 on: November 01, 2018, 02:05:53 PM »
I thought you fitted over-size pistons and rings? 5 or 10 thou is a lot of metal to hone off if the pistons are oversize.

What about 20 thou... as +020 are the new pistons. But it was that engine specalists plan to do it like that, and they carried it out, so they said. If you look back in the posts, there are all the details about this.

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #93 on: November 01, 2018, 02:16:40 PM »
It's a HUGE amount to do with a hone. And..... you would NEVER be able to keep the barrels straight and true with an engine hone no matter if you set it up in a drill press or whatever. They would be wide in the middle and narrow at the ends guaranteed.  Definitely needs to be done on the proper machine by an expert.

They talked about honing  and I think, indeed, the barrels aren perfectly straight, because that one piston that does seem a fraction larger (or deformed), when I push it through the barrels, the resistance is not equal everywhere.

And sure, that's exactly what I thought about honing. They way it's described, "never have the stones go out of the barrel" means everything away fro the ends of the barrel will be touched by the stones more than the ends.

So, Glort, I should go there and...

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #94 on: November 01, 2018, 02:35:20 PM »
The 20+ thou should be the original bore plus 2o Thousandths of an inch to get to the right size.
That size should allow for the required clearances as well.  Normally they would check the piston size, whatever it was then bore  to allow 1-2 though MAYBE for honeing/ final finishing and check that was over size enough to allow clearance for the piston fitted.

Maybe your guys got the numbers wrong, only bored and didn't do the final finishing, the pistons they got were from another similar engine and were 20 thou over that engines bore not yours or...... who knows?

Thing is whatever the size, the pistons should have had the required clearance in the finished bore whatever size that was and then the rings would also be ajusted to their gap even if the bore was not 100% to spec.
As the pistons and rings were very tight, the only conclusion can be the bores were not finished to the proper size for the pistons supplied.

If you are going to get a new Piston(s)  get them first and see how they fit. Might just turn out they do fit the bores correctly.  The finished size is not as important as it being correct clearance  for the pistons fitted.

 If you have any intentions of keeping the boat and running it for more than a few hours DO get a new rod. When you change the rod, put new bearings in.... both big ends. they will probably only come as a set anyway.  You do need to check the clearances on those as well and tightening the big end caps with a tension wrench is CRITICAL.  Install bearings, torque them down with a plastigauge or similar in place, unbolt, check clearance, if OK, put something like cam assembly lube in the bearings, reassemble and torque Down.


Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #95 on: November 01, 2018, 03:23:20 PM »
I wait for the manual t be delivered, look at the advised clearance, then check it with the one OK piston, and then see.

sirpedrosa

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #96 on: November 23, 2018, 02:16:33 PM »
Hi Rob

How things are going with your JP2?

BR
VP
Bernard 18A - 1968

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #97 on: November 23, 2018, 02:31:03 PM »
I've sent the engine workshop who bought the pistons and did the honing the info from the manual, about the exact measurements for the cylinder for a +020 piston and asked if they'd want to take a look into it all being right, and do another measuring, when I'd bring the stuff over. I also asked where they'd bought the new pistons because I wasn't all that happy with them being different from the originals at various points and that I considered doing some shopping again. I didn't mention any blame. Just the things as they are: I have these questions.

10 days later, still no response.

I got very busy with other stuff, though.
The plan, now, is to contact the two resellers of Lister Petter parts and see if they have pistons that look more, like the originals, preferably, identical!

I have ONE question, that I do not find the answer to in the manual: what the clearance should be between the piston skirt and the barrel!

Cheers
Rob

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #98 on: November 23, 2018, 02:33:54 PM »
I understand I may find the exact measures of the barrel and that of a piston, and then deduct and find the clearance.

sirpedrosa

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #99 on: November 23, 2018, 04:46:53 PM »
Hi Rob

see may thread (reply 131 >>): http://listerengine.com/smf/index.php?topic=8320.msg97563#new, and pay attention to 38AC's notes.

BR
Pedrosa
Bernard 18A - 1968

sirpedrosa

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #100 on: December 04, 2018, 12:04:54 PM »
Hi Rob

No news, good news, or not so?

BR
VP
Bernard 18A - 1968