1995 454 gen 5 - piston replacement

[mBurns]

So after some in-depth troubleshooting to my problem from a while back - we think we found the problem. Think it cross-fired, which blew the head gasket between #3 and #5 cylinders, and broke the #5 piston. engine is out, and on a stand - planning on dropping the oil pan tomorrow to check for metal. hoping the flakes are only in the upper half. the pieces are tiny. In addition, there was definitely a little bit of water in there too. source - i'm guessing up the exhaust manifold. the darn flappers were totally gone.

Anyway, I've got the heads at a local machine shop for repair, but I'm drawing a blank on the piston. Is there a way to purchase a single piston? I can only find sets..
1995 7.4L 454 w/ Bravo 3. SN 0F614755

shown below is cylinder 5

 

[alldodge]

You could probably go to a junk yard and find a piston.

IMO you need to bore the motor, look at the difference in piston gap, it appears (to me) the bore has dished out on the bottom. There is a difference side to side. maybe it's just the pic

 

[Scott Danforth]

You have the motor out. A set of cast pistons and a bore and hone job with new bearings is the way to go. Not just a single piston

 

[tpenfield]

Not sure you can get proper rotating assembly balance with replacing one piston. Usually is why they are sold in sets.

 

[flipbro]

Agree with Scott. Time to rebuild.

 

[mBurns]

well uh.. that certainly ups the cost of this repair then.. turns out what i thought was a set of pistons, WAS actually a single piston. looks like ~$200 per piston, and ~$100 for rings per piston.. so at a little over 300 per cylinder (not counting the machine job) 8 cylinders.. seems extremely overpriced. or am i missing something?

 

[alldodge]

No, you can get 8 pistons and rings for around $500 for the set. This is for .030 overbore size of 4.280 for original flat top with valve relief cut outs.
http://www.summitracing.com/search/...2+4294951398+4294951383+4294883983+4294880229

There are other types which run up higher
Here is a set of stock for under $300 for the set
http://www.summitracing.com/search/...94882392+4294951398+4294951383+4294883983+510

 

[Scott Danforth]

well uh.. that certainly ups the cost of this repair then.. turns out what i thought was a set of pistons, WAS actually a single piston. looks like ~$200 per piston, and ~$100 for rings per piston.. so at a little over 300 per cylinder (not counting the machine job) 8 cylinders.. seems extremely overpriced. or am i missing something?

Are you trying to buy thru a Mercruiser dealer? If so, Mercruiser buys from GM which buys from Federal Mogul. So yeah, buying a $36 piston that has been marked up 2.4 to 5 x each transaction would be pricey. As AD pointed out. Cut out the middleman. Many times your machine shop even gets pricing better than Summit

 

[mBurns]

Well, I use perfprotech dot com to find the part numbers for what I need - then google around the part numbers.. wasn't getting a lot of results. ebay had those pistons as low as like 210 apiece. I figured a piston should cost like 20 bucks. I'll give the shop a call after lunch and see if they can find me a better price. If they can't, I'll probably go with these guys: http://www.ebay.com/itm/261049346817...%3AMEBIDX%3AIT

full rebuild kit for 650. unfortunately for me, I already have all the gaskets I need for the rebuild. (jumped the gun and ordered stuff before I knew how deep the damage went).

thanks for the advice guys!

*edit* -- Dodge, I wasn't ignoring you post -- I'm just a little skeptical with the way summit racing doesn't specify how many a "kit" is. just says "quantity: sold as a kit". I'm sitting here like, well great. is a kit what's show in the picture for all 8 cyliners or just 1?

 

[alldodge]

No worries

I would suggest looking for a complete long block rebuild kit, but your machine shop could do that for you. If you do it, just need info from the shop as to bearing sizes for main and rods. Kit can include oil pump, timing set, brass core plugs, gaskets and seals

 

[mBurns]

Not sure you can get proper rotating assembly balance with replacing one piston. Usually is why they are sold in sets.

This might actually become another issue to deal with now.. Heard back from the machine shop -- turns out they don't make these pistons any more. and the "replacement" part is no longer made. so there's apparently a 2nd revision replacement part that is available - however the we're worried the weight wont be the same.

I dropped the oil pan, and pulled the bearings and the pistons today -- and surprisingly, the bearings were in remarkable shape. the 2 cylinders that originally had no compression were found with the top compression ring frozen. other 6 pistons had good rings. plan is to go ahead and replace all the pistons, rings and rod bearings (takin' y'alls advice) and the oil pump.

I can see where they drilled the crankshaft to balance it with the current pistons.. how likely is it that I'll have to get it rebalanced with the new pistons? should I go ahead and pull the crank too? (if possible, I'd like to mess with the timing as little as possible - this is my first rebuild..)

 

[Ibl0wstuffup]

I wouldn't skip checking and replacing the crank bearings while it's out. I would have the machine shop magna Flux the crank, heads, rods and block while it's apart.

https://youtu.be/rFSyCOiQe1I

 

[alldodge]

Heard back from the machine shop -- turns out they don't make these pistons any more. and the "replacement" part is no longer made. so there's apparently a 2nd revision replacement part that is available - however the we're worried the weight wont be the same.

Never heard of such a thing. Now if you were trying to get the exact same type then I'll agree, probably no longer made.

Pistons are made as a set, and while not balanced to the gram they are fairly close. If all pistons, rods, pins and bearings all weight the same your good. The crank is balanced to the crank. I have had several engines further balanced by finding the lightest and heaviest piston in the set of 8, then balance all to within a gram of one another. This is done by removing aluminum from the underside of the piston, doesn't take much, as before their pretty close.

Maybe I missed something in all these years of motors, and have been wrong before. So maybe some input from Bondo Scott Danforth Tailguner may comment

 

[flipbro]

Get one of your pistons off and weigh it. Then find pistons as close to the weight as possible. Be sure you don't end up with a heavier piston ring rod and pin then what your crank was originally balance 4. You don't want to be needing heavy metal added to the crank to balance the Bob weight out. It's very expensive.

 

[Scott Danforth]

They make pistons every day for the Mark IV, Gen V, and Gen VI motors (same parts)

Either get a set of pistons and give to the machine shop, or better yet, take the motor to a different machine shop because the one you picked doesn't know what he is doing.