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Discussion Starter #1 (Edited)
Little piston problem???

I am trying to figure out what I did to number 4 on a mercruiser 454. The temp sender was in the wrong location, so I don't if it got hot or lean. Also I noticed number three or number five had sunken the exhaust valve. I was running pretty for about five miles in my formula. I have also heard of other boaters having problems with mercruiser 454s on number 4
 

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Discussion Starter #3
750 vacume with factory jetting. 975 elevation and slightly tan plugs. I did have a very small blister on one plug but it came from the rear of the engine. I still had 123 psi of compression on that piston at 7100 altitude It was a poor rebuild sine the pistons are closed chamber.
Thanks for the reply
 

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Would be interesting to know the clearance at the time of the build. I would say it got hot.

Don't slam the builder for using close chamber pistons. Its common as dirt when trying to hit a specific compression ratio. There are only so many dome configurations on shelf stock pistons. By using CC pistons they can hit compressions higher than a flat top would give them, without going to high with a open dome. When the dome is that low, it does hurt anything, and it probably wouldn't have run any different with a lower open chamber piston.



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Discussion Starter #5
Thanks Bob It really was a poor build since the temp sender was in the wrong place. The exhaust valves were hitting the pistons, wich I know is common on closed pistons. The cam was too big and had Rhodes lifters to calm it down on the bottom (as was pointed out to me by the previous owner), the carb baseplate gaskets were Teflon and Glued on to the intake and ruined. Just a few things, I do very much appreciate your replies and your input but it was a crappy build. The builder was also the installer.
The good side is that it will be done right, I moved the temp sender to the intake by the thermostat already! The boat only has 182 hours on it, the same engine had previously dropped a valve when the boat had 140 hours on it. It only had 155 hours on it when I bought it. I just wish I had an accurate temp reading and this would have saved me a lot of trouble
Thanks for the input.
 

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If it was heat and because it was only one hole, sender location might have made a difference if it was on the head that got hot, if it was on the intake it would read the average of both sides of the motor and it might not show if just one side was burning down.
 

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Discussion Starter #7 (Edited)
Ya, but it wasn't in either head or intake it was in the wrong side of the big thermo housing that goes to the riser. I never worried about it running cold. I bought the boat took it to the cold lake here in colorado. It ran great and never was ran more than a few miles on a rough lake, so no sustained speed. I dragged it 12 hours to Missouri, rejeted it. Ran it hard for a couple of miles. Check front And rear plugs , nice tan color. Then the next day went for a longer trip ending with top speed(65) for a few miles and then boat started slowing and the rest is history. I went through the trouble of pulling exhaust and plugs. I also put in another thermostat. That is when I noticed the wire to the sender was a little short because the sender had been relocated. I did manage to salvage the weekend because it still ran pretty good besides the blow by!
 

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Would be interesting to know the clearance at the time of the build. I would say it got hot.


Yes, what was the piston to wall clearance and ring gaps on the build sheet.
The p/v clearance specs and required piston work.
Any builder notes ?

If the motor got hot it was not the temp sensor :))eek:)) fault

More like a water pump impeller that came apart
and screwed up your water flow

Went thru hell once finding all the pieces of a old impeller that failed
 

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Discussion Starter #9
Would be interesting to know the clearance at the time of the build. I would say it got hot.


Yes, what was the piston to wall clearance and ring gaps on the build sheet.
The p/v clearance specs and required piston work.
Any builder notes ?

If the motor got hot it was not the temp sensor :))eek:)) fault

More like a water pump impeller that came apart
and screwed up your water flow

Went thru hell once finding all the pieces of a old impeller that failed
I am not blaming the temp sender. But since it was in the wrong spot I was unknowingly seen low temps. No build sheet, but you'd be surprised how many machinest / builders here wouldn't clearance a boat any more than a car. The impellar was the first thing I changed when I bought the boat. I put about a hundred miles on it after I hurt it( I thought I had broken a skirt because it still had decent compression and had a full week planned at tablerock. The engine temp gauge works great where the sender is now , but too late and I will never know if and how hot it was or weather the piston simply expanded in a cold block. I hurt it July 4th weekend . Ran it x few more times here and just got around to pulling and fixing it.
 

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Would be interesting to know the clearance at the time of the build. I would say it got hot.

Don't slam the builder for using close chamber pistons. Its common as dirt when trying to hit a specific compression ratio. There are only so many dome configurations on shelf stock pistons. By using CC pistons they can hit compressions higher than a flat top would give them, without going to high with a open dome. When the dome is that low, it does hurt anything, and it probably wouldn't have run any different with a lower open chamber piston.
Looks like a stock Mercruiser piston to me.
, Leaned it out and over heated it . No truth in that mercruiser has a problem with #4 cylinder
 

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I am not blaming the temp sender. But since it was in the wrong spot I was unknowingly seen low temps. No build sheet, but you'd be surprised how many machinest / builders here wouldn't clearance a boat any more than a car

I see you are dealing with complete idiots !

A marine engine needs very special attention, they run a very high duty cycle,
like pulling a trailer up hill all day at or near wide open throttle.

I ship race motors to real experts, when needed.
You don't have to look very far !

Scott Foxwell and C Straub, excellent for heads and cams
Barry -obnoxious 001, excellent builder
Pfaff - ditto
Teague -ditto
Joey Grose-ditto
out here on the west coast.

But, you also need a sharp installer,
making sure everything is as it should be.

Better to pay more and know what you have is done right.
Than deal with the shit your going thru
 

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Discussion Starter #13 (Edited)
Grammer

Its most likely a JE piston that is very similar to those they supply for the Mercruisers.

But it is very obviously not an original Merc assembly.[/QUOTEIts a ,030 over closed chamber. Hopefully I can buy just one. I can't complain too much since it ran great, still has original interior and I only paid 8300 for her. Pics on first post. We gave some great machinest in the area. This rebuild was not done by one of them
 

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Discussion Starter #15
No, it will have to go .060. It is stamped L23490. It is a TRW. I will check into your SRP part number. I got an idea the builder had them laying around. What would cause an exhaust valve to sink? It was on the opposite bank. It was hitting the piston lightly. Heat, lean, soft seat or something else. Heads are 049s, the valve job/ seats were done by a pro. The builder was an assembly guy, not a machinest.

Thanks for the info
 

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Discussion Starter #17
No,only one piston was hurt, I was surprised how nice the other seven looked. But it doesn't matter much, I will do it right. The valve was on number 5. When I sell it I will be happy to know it was done right.
Thanks for the part numbers and I have heard you guys talk before about what bent valves do to seats Funny that the intake valve also left a perfectly round impression in the bad piston?? 4 pistons had ex dings and one had an intake impression. I think these pistons were used in another engine. The dome on 8 was hitting the head near the machined part of the chamber exhaust side thanks again for the help, I have learned a lot on this forum
 

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Might look into .040 over so you can hone it instead of boring to its max. I see the zero gap ring in the 3rd pic I wonder if there enough clearance. I have run them before in one of my engines without any problems so I am just asking.
 

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Discussion Starter #19
I wish I could go .040 but the cylinder will not clean up at .010 more. I'll check the gap on the other bores out of curiosity. The ZGS rings are kind of a dated idea now.
 
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