Should I replace this piston?

[Reggie08]

Pulled the pistons out of my motor over the weekend. I know I have to replace one, but there is another one I'm unsure of. The grooves that run along the outside of the piston are worn down to the point they're almost gone. Is this something I should go ahead and replace since I have the motor apart?

 

[Reggie08]

Re: Should I replace this piston?

Oh, and both cylinder heads have a few "dings" in em (#2 and #3 cylinders). Is this something I can have fixed up at a machine shop or do I need to replace em?

 

[marinegrh]

Re: Should I replace this piston?

Man, the first question I would have to ask is what caused such damage?. That #3 looks slapped around pretty good. What is the block like, are the sleeves as bad or can they be bored over. I would look at each very carefully. What is the HP and Year or this demon. When looking at piston replacement you also need to keep in mind that because you change the pistons, rings etc the sleeves are bored right and the root cause is identified and repaired so you dont do that damage to the new pistons. I'd look real good at the remaining pistons/sleeves and integrity of the powerhead before jumping into an afterburner. Post as much info as possible theres alot of great mechanics out here to help you through this

 

[marcysibyll]

Re: Should I replace this piston?

You have bigger trouble than just replacing pistons. First, determine what caused the damage, then fix that. If cyls have matching wear (grooves and scratches) they need to be addressed. A rule that I use when it comes to replacing things is, if you have to ask, it probably should be.

 

[Reggie08]

Re: Should I replace this piston?

The motor itself is an 85 'Rude 90hp with 140hp carbs and exhaust. The history behind the motor according to the guy I got the motor from is, the VRO went out. He initially thought it was a power pack. The last time he used it (a few years ago), he limped it back to the boat ramp, pulled the plug on the #2 cylinder and found it caked in aluminum. The #2 piston actually looks worse than the #3. He told me back in the mid to late 90's, he had the motor re-sleeved. The #2 cylinder has a little bit of aluminum transfer from the piston and the #3 has a little bit of scoring. However, I won't be using this block. I'm getting another block to rebuild. The existing pistons I believe are .030 pistons (they're stamped "030" on the ends) so the new block will be bored .030 over.

I've been told having the 140 carbs and exhaust caused the motor to run lean. I don't intend on putting those carbs and exhaust back on. I'll stick with the 90hp. A buddy of mine in Iowa (boat mechanic) told me he thinks the fuel/oil mix wasn't getting into the #2 cylinder causing it to burn up. So I'll also be installing new fuel lines.

Right now, I'm not out any money save for my time and a few dollars for an OMC Parts catalog and Service Manual. But I do plan on rebuilding the motor while taking my time. I intend to rebuild the carbs, replace the t-stat and install a new VRO (but I'll pre-mix my fuel and oil to 50:1 instead of using an oil tank) and whatever else I think needs/should be replaced/rebuilt to give me a warm fuzzy before cranking this motor over.

Here's a picture of the #2 piston and the respective spark plug.

Edit: Additionally, in my haste to tear into this thing, I neglected to perform a compression test.

 

[iwombat]

Re: Should I replace this piston?

VRO failure does not only effect one cylinder. Your whole motor would look like that. If you're planning on premixing you'd be better off replacing the VRO unit with a plain old fuel pump and saving yourself a couple hundred dollars.

If you've only got one cylinder with this problem, it is more likely a clogged carb jet. You'll want to really inspect the bearings carefully, or just replace them. If the upper cylinder didn't get lubed the crankcase probably didn't either. Like was said before, you'll need to go up at least one overbore.

If it were mine, I'd be taking all the pistons to the machine shop and have them checked for roundness and matched to the bores. Let the machinist make the call.

 

[captbjack]

Re: Should I replace this piston?

VRO failure does not only effect one cylinder. Your whole motor would look like that. If you're planning on premixing you'd be better off replacing the VRO unit with a plain old fuel pump and saving yourself a couple hundred dollars.

If you've only got one cylinder with this problem, it is more likely a clogged carb jet. You'll want to really inspect the bearings carefully, or just replace them. If the upper cylinder didn't get lubed the crankcase probably didn't either. Like was said before, you'll need to go up at least one overbore.

If it were mine, I'd be taking all the pistons to the machine shop and have them checked for roundness and matched to the bores. Let the machinist make the call.

not sure about that i once had a suzuki 115 that burnt 1 piston. (oil line to the carb came off) not sure if this motor has individual oil lines or not.

 

[Faztbullet]

Re: Should I replace this piston?

That damage could be from fuel due to a partial stoppage of the high speed jet. I doubt it being a fuel supply issue as carb shares single float for #3 & #4. From the looks, I say it is a preignition issue due to overadvanced timing or bad bias circuit in one of the packs.

 

[emdsapmgr]

Re: Should I replace this piston?

The fact that the carbs are from a 140 should not be the issue. The 140 carbs should have been able to supply plenty of fuel to that engine. I would also be interested in what the high speed jets look like from the carbs. If the prior owner had a cracked reed, it could also run lean on one cyl, so check them closely. If the engine has the recirc system, be sure all the hoses are in good condition, and not cracked, leaking. That one cyl does look like the timing was too advanced. It may not have been set at high rpm. Another possibility: one side of the block overheated and no horn went off.

 

[Reggie08]

Re: Should I replace this piston?

If you're planning on premixing you'd be better off replacing the VRO unit with a plain old fuel pump and saving yourself a couple hundred dollars.

iwombat,
I'd much prefer to go that route you suggest. Any idea where can I find a good part number for the proper fuel pump?

That damage could be from fuel due to a partial stoppage of the high speed jet

That's exactly what my buddy in Iowa said (I said "fuel line" which, after re-reading my emails from him, I now know is wrong) The carbs are going to get a thorough cleaning

If the prior owner had a cracked reed, it could also run lean on one cyl, so check them closely.

I'm going to check the reeds out real good. I noticed one set of reed valves has small pieces of aluminum from what I am assuming is the #2 piston. Is there a good/proper way to clean them without disassembly? I just received my service manual yesterday in mail and glanced over the leaf valve section.


The crank looked as if it had plenty of oil all over. No signs of scoring or having gotten hot. The needle bearings and cages on all 4 rods look good as well with plenty of oil around them as well.

Based on what I've read in this thread thus far, I need to make sure the advanced timing is set properly (just read about that this morning in the manual) and make sure the high-speed jets are clear and carbs are cleaned. Maybe check the powerpacks as well?

 

[iwombat]

Re: Should I replace this piston?

Reggie, what model # are we talking about here? If there was a SPL version of that motor for that year, just lookup the fuel pump for that model. Really, there isn't a lot of difference between fuel pumps that use a hose (as opposed to mounting up over the pulse port), mounting is the only real issue.

 

[Reggie08]

Re: Should I replace this piston?

The model number is E90TLCOS.

 

[iwombat]

Re: Should I replace this piston?

A couple of threads for you to read:

"http://forums.iboats.com/showthread.php?t=213623&highlight=vro+pump+conversion"

"http://forums.iboats.com/showthread.php?t=202794&highlight=vro+pump+conversion"

 

[Dhadley]

Re: Should I replace this piston?

What spark plugs were in it?

 

[Reggie08]

Re: Should I replace this piston?

Off the top of my head I couldn't tell ya but I'll try to find that out tonight when I get home from school.

 

[Reggie08]

Re: Should I replace this piston?

What spark plugs were in it?

Champion Spark Plugs QL77JC4

Manual calls for QL77J4.

So it had the correct plugs in it from what I can tell.

 

[emdsapmgr]

Re: Should I replace this piston?

If you think any of the reeds are damaged, why not consider a set of composite reeds? Use the cages and replace the reeds. There are benefits to them, from an idling and midrange perf. standpoint.

 

[Reggie08]

Re: Should I replace this piston?

I've actually been giving it some thought to replacing them if for nothing else, because I have the motor broke open and it's one less thing to have to worry about in the future.