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Author Topic: New pistons Petter PJ2, block after short time engine running. Clearance?  (Read 2101 times)

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #30 on: October 22, 2018, 12:32:15 PM »
Does anyone have a tip for the best way to remove the piston rings? I'd of course do it extremely careful, but I don't know what I don't know. The scraper ring has a spring in the gap. Would that thing cause a problem?

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #31 on: October 22, 2018, 12:42:40 PM »
How many times have you run the thing when it locked up? Was it ever under load or making any power as in above idle?
Locking up an engine like that is a mechanical cringe fest.  Hopefully nothing bad has happened.

Also you will probably want new head gaskets as well. 

Hi Glort
I ran the engine a few times with no load. The first time it stopped itself after 2 minutes. The second time, I stopped it when it slowed down. The third time I had it run as slow as possible, no load. It then slowed down after 9-10 minutes so I turned it off. After each time it was impossible to turn the flywheel by hand, for like a minute or two.

The head gaskets I cut from material with metal thread in it, especially made for the hottest parts of an engine. Don't know the name of it. It's been awhile that I bought it. But yes, I'll cut new ones.

I'm very curious to see what the ring gaps are, tomorrow!

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #32 on: October 22, 2018, 02:09:09 PM »

The rings are removed as they say in the classics, Reverse of installation.
You just carefully spread them and ease them over the top ( or bottom) of the piston. You can put something thin like feeler gauges between the rings and piston and slip them over that way but as long as you open the part where  the gap is and ease that up and over you should be right. just be careful and try to spring them as little as you can.  I normally lift one end and then work the ring around till it pops off but see what feels best.  Just go slow and gentle.

It sounds like the damage may not be significant. Lot different to having the thing working hard and welding itself together.
I have no experience with engines locking up this way. Normally it is lack of oil or overheating or they become one in the same.

You have the best chance of getting out of this as easy as possible which is good.


Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #33 on: October 23, 2018, 05:28:11 PM »
PJ1 and PJ2 ring end gap  .029 to .037 inch
bump clearance .036 to .042
bore 3.8175 to 3.8185 inch

dieselgman

Hey dieselgman, I just measured the gaps of the first pistons' rings, when taken from the piston and put into the cylinder at the top side, and that was a bit over 0,4 mm, less than 0,45 mm being around 0,0165 inches.
(Photo attached to next post)
So, then indeed, the gaps are too small. They'd need double the size.

It means that ajaffa1 was spot on with his first comment!

Now shit happened. I still broke the 4th ring, the scraper ring. Dang! Got a bit confident I guess after the first three went OK. So, I'll see if Jim Perkins has one for me, part from the manual and an oil banjo bolt (replacing a wrong one put in by the life boat's former mechanic) he'll mail to me.
I still have the old pistons with intact rings, but they're a fraction thinner. I guess, worn a bit. What you think, guys? Would that indeed be a cause a problem?

I also see the tiniest vertical scratches, all the way down, in the wall of the first cylinder I just removed. How would I know which scratch is severe enough to demand new honing? And what if a second honing means a tinier wider cylinder, for the same pistons?

« Last Edit: October 23, 2018, 06:34:34 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 23, 2018, 06:02:26 PM »

If you se a line ( or several) run your fingernail across them and see if you can feel them.  If you can, will definitely need a hone, if you can't.... probably OK.

Be interesting to see some pics of the rings in the bore, the insides of the bores and the piston walls.

Hi Glort,
I now see you already gave an instruction to see if the scratches caused by too cramped piston rings are a problem. Most of them I can not feel with the nail. One I felt, though. I'll check again, all around.
« Last Edit: October 23, 2018, 06:32:05 PM by Rob PetterPJ2 »

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #35 on: October 23, 2018, 07:34:40 PM »

Yep, Bob is a clever fella with a nose for potential problems.  I don't think too many people would have picked that one up straight off the bat!

So far you are very lucky.  Hopefully the other Bore is just as undamaged.

As far as using the old rings, it would seem likley that they overbored the cylinders when they did them and the pistons are also larger. You'll need to know what size they went over. Generally the first oversize is  5 thou. If this is what they did which is likley, You'll need to tell the guy you are ordering the broken ring from. You won't be able to fit an old ring if the thing has been over bored.  Have a look at the pistons. They may have something like +.005 stamped in the crown. Might also be .010 if the bores were heavily scored or worn to start with.

When you rebuilt the engine, Did you do any of the bearings or just the top end? Also, did you get the specs for the head bolts and torque them down with a tension wrench in the correct order to the right specs? If not, best you do this time.

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #36 on: October 23, 2018, 08:10:11 PM »
As far as using the old rings, it would seem likley that they overbored the cylinders when they did them and the pistons are also larger. You'll need to know what size they went over.

When you rebuilt the engine, Did you do any of the bearings or just the top end? Also, did you get the specs for the head bolts and torque them down with a tension wrench in the correct order to the right specs? If not, best you do this time.

Ah, yes, of course. The engine revision guys said they'd order slightly bigger pistons, because of the honing.

I didn't do any bearings. I took the cylinders off, and removed the pistons. Nothing else.

And with the reassembly I followed instructions for how to bolt in the right order as I wrote earlier. No 'force meter', but an instruction of how the force used should feel/ I don't have all the specialists' tools.

I MAY BUY ME ONE, though, after reading about the importance of it (protecting the gaskets).

« Last Edit: October 23, 2018, 09:26:04 PM by Rob PetterPJ2 »

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #37 on: October 23, 2018, 08:40:12 PM »

Have a look at the pistons. They may have something like +.005 stamped in the crown. Might also be .010 if the bores were heavily scored or worn to start with.

The new pistons say 020 at their top side.... I guess that's 0.020 inch extra, then.
The old pistons have "196695  S" engraved, there. Now what can that mean?

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #38 on: October 23, 2018, 10:34:02 PM »

New Pistons are  20 thou over. Old rings definitely won't fit that large.
The old pistons probably just have the part number on them.  The S could be part of the part number or stand for something like Standard Compression.

You might want to feel the Rods and make sure there is no freeplay in the bearings. If there is any detectable movement especially in the big end, You'll want to do those as well whether it's a big job or not. Otherwise you could do damage and be pulling the whole thing down again anyway pretty soon.

Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #39 on: October 23, 2018, 10:44:53 PM »
You might want to feel the Rods and make sure there is no freeplay in the bearings. If there is any detectable movement especially in the big end, You'll want to do those as well whether it's a big job or not. Otherwise you could do damage and be pulling the whole thing down again anyway pretty soon.

You're not making me happy with this... I expect horizontal movement to be not a problem (even a necessity). Vertical it would be problematic. Before I did not feel any vertical freeplay, when I checked it for that purpose.

ajaffa1

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #40 on: October 23, 2018, 11:27:01 PM »
Hey Rob, looks like you may have dodged a bullet if the scoring is only very minor. A cylinder honing tool should fix the problem without having to do another re-bore. A tool like this is cheaply available in the UK https://www.ebay.co.uk/itm/CAR-ENGINE-CYLINDER-BRAKE-HONE-BORE-HONING-FLEXI-SHAFT-TOOL-51MM-TO-178MM/222367752202?epid=1146057264&hash=item33c626a00a:g:Ur8AAOSw2xRYbWnC:rk:3:pf:0

I know the purists are going to start throwing spanners at me for recommending such a low tech solution but you are only trying to knock the high spots of the scoring.

After honing clean the cylinders and then clean them again! (detergent and water and lots of clean rags) Now check the piston ring gaps and adjust as needed.

If you contact the machine shop that provided the pistons, their supplier should be able to send out a replacement piston ring. Might be worth asking for a complete set in case you break any more during assembly.

Glort is right about checking for play in the big end bearings, does your engine have a crankcase door? If it does then the cost of a new gasket and a pair of white metal bearing shells is a no brainer.

Bob

sirpedrosa

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #41 on: October 24, 2018, 12:37:29 AM »
Greattings to all

Sometimes I feel the same as Rob, but the guys around here have a long-standing experience - that's what I call masters.

I'm afraid the workshop where Rob had the job done knows less about it than he does.

As we say - a problem never comes alone! and maybe they've seen the bottom of Rob's pocket.

And also, as I had already said: "the machine works as it wants and not as we wish!"

Of course sometimes we doubt what our eyes are seeing, but the engine starts to take its weight in gold! and that does not cheer anyone.

Rob, dismantle the whole engine and resemble it again, each step makes sure that the whole assembly rotates freely - attention to the clearences because the engine heats up.

I'm sure it will get better!

Cheers
VP
Bernard 18A - 1968

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #42 on: October 24, 2018, 01:14:02 AM »

I know the purists are going to start throwing spanners at me for recommending such a low tech solution but you are only trying to knock the high spots of the scoring.

Dunno about that Bob. I don't think it's the low tech solution, I think it's the right solution.
Bores have just been done, it's only a bit of light scuffing... so far.  To bore them again and have to go to more new pistons and rings would be I think idiotic.
Like you said, run the hone round to knock off any high spots and that's it.  Not an F1 or Aircraft engine being built here.  :laugh:

Rob have you got the other piston out yet and have you also checked the pistons for signs of scuffing? I doubt now the pistons will be too tight BUT, I also don't know what effect having the rings so tight and jamming may cause as well.

Have to laugh at the description of the Hone.... BRAKE hone...... 51mm to...... 51 MM would be some BIIIG arse brake Cylinders! Maybe if you are working on Terex Mining trucks but...... Hmm. Then again, if you were working on anything with a 7" bore at the other end of their capacity...

RR Merlin was only 5.4".  Maybe for a ship engine 7" would be handy..... and then it would be the right tool for the brake Cylinders on them as well!   
Oh, ... wait.... Never mind!  :laugh:


Rob PetterPJ2

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #43 on: October 24, 2018, 08:10:31 AM »
Now I'm confused. In a catalogue in Dutch, the "schraper-veer", which, to me, seemed the Dutch word for scraper ring, is not the one I thought it was.

The one I broke was the 4th one, at the bottom side of the piston. It hides a spiral in it, that goes all around the piston and it has horizontal slits in its side. The Dutch catalogue has another name for it, with the word for "oil" in it.

What's its proper name in English, for the bottom ring that I broke?

Jim Perkins says he may have one, the plus .020 size. He's going to send me some stuff anyway. Otherwise I contact the online lister-petter shop.
« Last Edit: October 24, 2018, 08:21:19 AM by Rob PetterPJ2 »

glort

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Re: New pistons Petter PJ2, block after short time engine running. Clearance?
« Reply #44 on: October 24, 2018, 10:10:15 AM »

The bottom ring is often called the oil ring or the oil control ring.  The scraper ring is generally the 2nd ring down although may be the 3rd if there are 2 compression rings. It's usually tapered ( although might be hard to see) and also helps control the oil on the bore for the Compression rings and to steady the piston in the bore and keep it centred.

The oil rings are  hollow or have slots cut in for the oil to pass through and go back to the sump through the holes in the piston.

The extra piece behind the oil ring is the expanded. It's job is to help the oil ring exert more force on the Cylinder wall as the oil ring is supposed to have the greatest force on the bore of all the rings.
The top ring especially is helped to be forced against the bore by the combustion/ compression getting behind it and helping force it out but that doesn't happen with the oil ring which is the lowest on the piston.