Slant Six Forum
https://slantsix.org/forum/

Opinions on reusing a slightly damaged piston
https://slantsix.org/forum/viewtopic.php?t=63359		 Page 1 of 3
Author:  JukkaK [ Sun Mar 03, 2019 8:55 am ]
Post subject:  Opinions on reusing a slightly damaged piston
Hi,

My 225 Slant six has several broken piston rings. Cylinders are fine and not even worn that much so I'll hone them and install new piston rings. All the pistons seems to be fine except one, it has slight damage. Do you think that I can still use this piston since the damage is only in the upper part which doesn't need to be sealed by the rings.

I can remove any rough edges with a fine sanding paper plus the piston is softer material than the cylinder so I don't see any problems still using this piston. What do you think?

Attachments:
20190303_183713-768x1024.jpg
20190303_183713-768x1024.jpg [ 168.6 KiB | Viewed 6684 times ]
Author:  Badvert65 [ Sun Mar 03, 2019 9:01 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Look for cracks and make certain that the ring lands are not pinched (rings move freely). You will likely be fine.
Author:  JukkaK [ Sun Mar 03, 2019 9:08 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Quote:
Look for cracks and make certain that the ring lands are not pinched (rings move freely). You will likely be fine.
There is a slight pinching point which can be seen in the pic but I can carefully work that off. And of cource I'll check the clearances with the new rings. Thank you for your answer!
Author:  GregCon [ Sun Mar 03, 2019 10:07 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
There are a bunch of 'why's? that go along with this....like why did those marks happen in the first place, and why are rings breaking? I was expecting to see a nicer looking piston...that one looks like it's seen a hard life. Will it run? Of course. But why use it? New ones are $16...unless (from your name) you are not in the USA.
Author:  JukkaK [ Sun Mar 03, 2019 10:34 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Quote:
There are a bunch of 'why's? that go along with this....like why did those marks happen in the first place, and why are rings breaking? I was expecting to see a nicer looking piston...that one looks like it's seen a hard life. Will it run? Of course. But why use it? New ones are $16...unless (from your name) you are not in the USA.
This whole thing wasn't something I expected and/or prepared for, it is already going well over my budget, and no, I'm not from US so there's that.

I know what you mean by the why's. Why there are so many broken rings? Only answer I can think of is that somebody installed them using too much force and didn't use proper tools and technique. Why the piston looks like that? Well in that cylinder the top compression ring was in many pieces and propably one of the pieces got stuck in between the piston and the cylinder temporarily, maybe it eventually got out through the exhaust. The valve and valve seat had pretty bad scoring in them too.
Author:  slantzilla [ Sun Mar 03, 2019 11:43 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
That cylinder has been detonating. IMHO that piston is junk. You can roll the dice and try it, but I wouldn't.
Author:  GregCon [ Sun Mar 03, 2019 1:10 pm ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Yea, I agree it's detonation. Back in the olden days, we used to run 440's with the stock cast pistons on crummy unleaded gas...you could never get enough timing in without rattling. When we'd finally take the engine apart all the ring lands would fall on the ground. The rings, too.
Author:  JukkaK [ Sun Mar 03, 2019 9:16 pm ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Quote:
That cylinder has been detonating. IMHO that piston is junk. You can roll the dice and try it, but I wouldn't.
Well, the timing was way too advanced when I got the car so you might be right. About the piston...what do you think are the risks of reusing this piston? I mean if I'd carefully remove any rough edges and make sure that the ring groove is ok and the ring has proper clarance in the groove. To my understanding this top part of the piston doesn't really touch the cylinder walls.

Don't get me wrong, I have no intent to argue, I'd just like to hear the reasons why it wouldn't work.
Author:  slantzilla [ Sun Mar 03, 2019 10:28 pm ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
I would really be afraid it's going to continue coming apart.
Author:  emsvitil [ Mon Mar 04, 2019 1:22 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Quote:
I would really be afraid it's going to continue coming apart.
the ring lands could just about be ready to break apart...…………..
Author:  DadTruck [ Mon Mar 04, 2019 1:51 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
If there is a concern over cracks in the ring lands due to detonation,
Get the piston really clean then inspect the ring lands with dye penetrant.
Either a zyglow type that uses black light or the dye that uses a white powder
as a developer.
I don’t think the crack inspection technique that uses metal shavings and a magnetic
field would work on non ferrous.
An engine machine shop that works aluminum heads would have the ability to inspect the pistons for cracks.
Author:  ceej [ Mon Mar 04, 2019 6:54 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
What did the cylinder mic at? What's it going to mic at once it cleans? Is it the only one?
What size is that piston?

I'm with Zilla. Pitch it before it breaks your enigne. Not worth the chance.
If it's the only piston that was detonating, why?

CJ
Author:  JukkaK [ Mon Mar 04, 2019 7:44 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Well, you guys wonder why would I use this piston and I get it, I would wonder the same thing.

There are couple of reasons for it, one is budget, this whole thing wasn't something I prepared for. The other reason is that because the piston pin is pressed fit in the connecting rod and there are risks in removing those piston pins. The fact is that replacing just one piston isn't possible, or maybe it is but I would have to weight all the pistons to make sure that they are the same weight, without doing that it is basically the same kind of gamble.

Now, why wouldn't I just wieght all the pistons to make sure that the new one is the same weight? Removing piston require the removal of the pressed fit piston pin. If something goes out of spec or breaks during the pin removal then the connecting rod and piston pin is likely going to be junk. If one connecting rod gets ruined the possibility for me having to get all six new connecting rods and piston pins increase dramatically because the connecting rods need to be the same weight too. In that case the engine wouldn't get assembled because I couldn't afford it. Also, I would need to buy the right tools for pressing out the piston pins, that isn't cheap either. The same thing about the piston pins and connecting rods getting ruined in the process of the removal is mentioned in the -66 Dodge Dart service manual.

I had a talk with an old guy I know, he has built all kinds of engines professionally and as a hobby from a daily driver application all the way to the racing engines for at least 50 years and he told me that it isn't even uncommon that in the process of removing the pressed fit piston pin it just goes out of spec, even if it doesn't seem to get damaged or anything but when it is put back together the fit is too loose. His main concern for these pistons is that the ring grooves are too worn and the clearance when the rings are installed will be too big, that I won't know until I get the new rings.

Of cource this damaged piston is a risk, everybody knows that. I'm just weighting my options here and calculating the risk/cost ratios. It migt be a good idea to run this piston by a machine shop to check for any cracks if they are able to do it with the connecting rod attached to it.

Like I said, my purpose here isn't arguing about this and all the opinions and ideas are appreciated!
Author:  JukkaK [ Mon Mar 04, 2019 7:51 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
Quote:
What did the cylinder mic at? What's it going to mic at once it cleans? Is it the only one?
What size is that piston?

I'm with Zilla. Pitch it before it breaks your enigne. Not worth the chance.
If it's the only piston that was detonating, why?

CJ
Haven't measured them yet but the block seems to be bored into maximum size, it says +060 at the top of each piston. Cylinders actually don't seem to be worn that much from the last time they were bored. My options are quite limited here.
Author:  GregCon [ Mon Mar 04, 2019 10:06 am ]
Post subject:  Re: Opinions on reusing a slightly damaged piston
1) I wouldn't worry one bit about the weight of a new piston. It'll be 'close enough'. Balance is a greatly misunderstood topic when it comes to reciprocating engines.

2) I recently pressed out the pin on my Six and used a Dake press. I can tell you from experience that it took around one ton of force. I made no effort to protect the pistons skirts - they were sitting up against the steel bed of the press - and they were not damaged. If you did want to reuse the piston, you could cushion it with some wood and it would be fine. You could even make a puller with some 1/2" all thread that would suffice, if you don't have a press.

3) Don't know where you live but in most parts of the world there is a machine shop that has an electric or propane heater that is used for piston pin fitting. It's cheap.


It might cost a few dollars to replace the piston but it'll cost you way more to pull the engine back out and go through it again if the ring lands give up 300 miles down the road.
Page 1 of 3 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/