Piston is damaged...replace?

[Mokkan]

I've removed my head to replace valves since a previous owner let the timing belt wear out and slip. The pistons showed signs of valve kissing, but nothing too serious. Then I took a closer look at piston #2 and found damage at the very edge of the piston face, enough to leave a visible mark on the cylinder wall. I can not feel the mark at all, so it is not into the metal. My gut reaction is to replace the piston. My second thought was to remove and file/sand the damage smooth. I'm planning to leave this engine stock, so I won't be running crazy boost or anything.

A. Is either step necessary?

B. If so, will repairing be sufficient (with new rings)?

Engine 4G63T - 1990 w/ 162k miles

Compression test (damaged valves):
dry - 30psi
wet - 42psi

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[lowcashleblanc]

I would replace, in my mind those spots can prove to be failure points due to metal expanding and contracting from heat cycles. It may not happen right away or even a month or 2 from now, but could still possibly happen. Safe move would be replacing or either taking them to a shop for inspection. Either way your gonna have to remove it to safely work on it. Might as well have somebody knowledgeable take a gander.

 

[Mokkan]

I'm planning to run this in a stock SCCA class for rally cross, which would require OE or OE replacement pistons. I'm not familiar with dsm aftermarket suppliers yet, would topline pistons be considered OE replacement or a performance upgrade?

 

[nfernotalon]

They are oe replacements. Theyre not forged. How would they know what piston or rod youre running anyway?
http://www.extremepsi.com/store/product.php?productid=18466&cat=1362&page=1

 

[5150DSM]

A little quick dremel work and that piston would probably be fine. Personally, I would suggest a basic stock rebuild which could be done for under $1000.00 including machine work and gaskets, if you do the work yourself. The peace of mind is more than worth the expense.

 

[Mokkan]

Personally, I would suggest a basic stock rebuild which could be done for under $1000.00 including machine work and gaskets, if you do the work yourself.

I've got about $800 worth of parts on order. Gaskets, pulleys, belts, valves and a new exhaust manifold...

How would they know what piston or rod youre running anyway?

They wouldn't. Honor system and all...

 

[nfernotalon]

I've got about $800 worth of parts on order. Gaskets, pulleys, belts, valves and a new exhaust manifold...



They wouldn't. Honor system and all...

Yea let me know its the same ones from that link. Save yourself a few bucks.

 

[Nitrobasher]

Replace the piston and try honing out the cylinder. If you can buff the scratch out there shouldn't be an issue.

If you have the time however it would obviously be beneficial to tear the block down and get it inspects/cut.

 

[Mokkan]

Alright, I've got new pistons on the way. Now I have to remove the old ones. I've read all the guides that seemed relevant, but did not get an answer to this question:

Can the pistons be removed with the block still in the frame?

I'm hoping I can jack up the engine, remove the pan and access the rod caps. Is this the case, or do you have to remove the front case and oil lines as well?

 

[Afizzle]

The piston is damaged and you want to know if you should replace it.

kinda answered your own question there.

 

[Mokkan]

The piston is damaged and you want to know if you should replace it.

kinda answered your own question there.

Not all piston damage requires replacement; valve 'kisses,' for example. And yes, I was looking for confirmation of what I already knew.

Regardless, now I'm trying to find out if it is necessary to remove the block from the car in order to remove the pistons or if it can be done while the block is still in the frame.

 

[keveka2]

No you can leave it in the car just be sure not to get the rod caps mixed up and your going to have to take the pistons and rods to a shop.. For the pistons to be pressed off and then the new ones put on... If it was me I would of popped the piston and rod out and filed it down and let it ride.. I've done this before and never had any kinds of probs with it.....

 

[91fwdnightmare]

Get yourself a ball hone and a drill and give it a couple licks infact do them all to knock all the fuel off the cylinders without taking material out.

 

[Mokkan]

Awesome. I've already invested enough in new tools without looking for a hoist and stand.

I'm taking the pistons to a shop fore sure. I've gotten in enough fights with presses in my life to be willing to pay someone else to deal with that.

Honing is probably a good idea too. I was initially against it, but I think I was just against the thought of more work.

 

[Afizzle]

as you know you can remove the piston w/o removing the block. Oil pan comes off and the cranks right there. 2 bolts and the piston comes out.

A little trick to hone without getting metal shavings on the crank, make a cardboard cutout of the exact dimensions on the cyl wall and wrap a shop towel/rag around it and shove it all the way down. if its done right and snug enough there should be no metal touching your crank

 

[nfernotalon]

Your pistons are on the way! I can usually man handle the shortblock out with no head id rip it out of the car makes life easier in the long run or get a buddy to help you.