Weird Engine Issue

[ESPNSkier]

I have a 1993 MasterCraft ProStar 205 with an Indmar 351 with about 1,100 hours on it and it has been running great. However, last week as I was coming into the course the engine blew out the spark plug in cylinder #2. As it turns out I have a cracked head and I'm replacing both heads. The weirdness happened when I pulled the heads and discovered that the piston in Cylinder #6 (2nd cylinder on the port bank) is rotated upside down. If you look closely at the 2nd image you can see the word "Up" and an arrow....pointing down! I have owned the boat for more than 19 years and the engine has never been apart so I assume that it was assembled with one piston reversed at the factory. Should I be concerned or just put the new heads on and hope for another 1,100 hours?

 

[oldjeep]

If the valves haven't contacted the piston in the last 1100 hours it should be just fine as long as the new heads don't require more valve clearance than the old ones. It is interesting though ;)

[ESPNSkier]

Thanks @oldjeep, that's what I'm hoping!

[bigskieridaho]

I would change it around if you are going to put new heads on it. The clearances won't be the same, and it wasn't right in the first place. I know it means pull the engine, but will be a piece of mind in the long run. You can leave it, but I wouldn't. Easy to pull....Git er dun!

[gregy]

nice quality control there. Some Ford tech was asleep that day.

[303Skier]

So weird! Was installed that way or the rod broke. I'd install new heads and then hand rotate crank and feel for any binding. remove all spark plugs.

[cruznski]

Since you have it all down to this level I'd pull it and rotate that piston- it's just not right. Kind of a testament to the tractor nature of those motors, but still you aren't that far away from correcting what was a factory major faux pas.

[DanE]

Turn it around, there is more to pistons than meet the eye. For instance bore for the piston bolt could be assymetrically positioned. The recesses are not for valve clearance they are combustion chambers. probably has a slight efffect on intake and exhaust breathing of that cylinder as well as mixture when the chamber is assymetrical like that ( looks like it ran a little richer than the others)

[DmaxJC_ski]

19 years and over 1000 hours..... if you are using a stock replacement head, I would run it. And if your concerned about clearance run a thicker head gasket.

[wettek69]

Take it out and get the piston put in correctly. Piece of mind. That would nag me until I gave up and pulled it, once I had seen it.

 

"Fix forever, or forever fix."

[Stevie Boy]

Aircraft Engineer, I would not be able to live with myself, if I ignored it, think about it, you go to all the trouble to, put nice new heads on it, and the bottom end gives out, or the piston makes contact, no good just turning the engine over, to see if it makes contact, when the engine is running there is certain amount of throw, with some wear as well, that piston could travel quite a bit more and make contact.

[oldjeep]

I'd be more concerned with opening up the bottom end and getting a case of the might as wells. Once you pull a rod bearing, might as well replace them all. While you are at it might as well replace the crank bearings. Have to take the piston out, might as well hone the cylinder and put in new rings - can't do just one so might as well do them all.

Once that engine comes out, might as well just do a full refresh;)

[Gloersen]

The time and effort to rotate that piston will not likely provide any gains considering the history; it'll just reduce water time.

 

diligently prep the block's mating surface for the new head gaskets, use new head bolts, replace with new heads and... go ski!

 

 

[Stevie Boy]

Out of interest, 1100 hrs, how many hours left before a Engine refresh is likely to be required ?

[ESPNSkier]

Thanks all, great advice here! Given the time of year, I agree with @oldjeep and @Gloersen and plan to put on the new heads and hope for the best. These are GT40 heads and the Machine Shop is telling me that these heads have a crazy amount of clearance. If it was December I would most likely pull the engine and do a total refresh. As @oldjeep said, once I pull the pan I would pretty much have to do a total refresh....maybe next winter. @Mark_Matis, I believe you hit the nail on the head as there was significant blockage in the cooling passages which I'm sure contributed to the cracked head and is probably related to low water levels this spring.

[kdeupser]

Don't tear that motor down just to flip the piston. It will probably destroy itself if you flip it since it's worn in upside down. If you have any concern about piston to valve clearance just clay one piston and then mic the clay.

 

Those are very low compression pistons anyways so you should be fine. I've seen the 351 windsors go for 2 to 3 thousand hours.

 

I would probably go with a head from "Trickflow" if I were you. Then when you see the need to freshen up the bottom end I would go with at least flat top pistons with a mild cam. That engine is easy to make respectable power out of so good luck.

[spicoli]

I believe the piston dome is designed like that for a reason and really should be installed right way will it work, well it has been but that don't make it right.but I'm with old jeep if u pull it might as well put new bearings and ring it why not all that money brand new heads take your time do it rings and bearings are cheap compared to heads if you jump on it it won't take long turn few bolts o yea don't forget new oil pump and water pump

[spicoli]

O yea and what if the connecting rod is backwards then the oil holes could be off some

[Ski_Dad]

i personally would leave it - it has worn in the way it is. Cleaning the crud from the cooling passages is more important - i have 2 friends with same vintage MC engines that lost a cylinder due to the crud build up.

[MISkier]

I have heard of overheating in a specific cylinder and melted piston due to poor cooling created by silt blockage in the engine. Apparently, it eventually hardens to concrete inside the block.

[ESPNSkier]

Thanks @Mark_Matis, I may need to do some plumbing work this winter.

[Fast351]

The other thing about flipping that piston is that the rods are NOT symmetrical. The chamfer on the crank side of the rod has a bigger radius than the side that contact the adjacent rod. That means you have to flip the rod in the piston. This is not something you can do by hand without special tools since the piston pin is pressed into the rod. Machine shops use a special torch jig to heat up the small end of the rod so the pin can be pushed out.

 

Personally I'd leave it. Who knows what kind of strange wear patterns you could develop by putting a piston in that's used.

 

[Fast351]

@Stevie Boy It really depends on how diligent the owner is with maintenance. Generally speaking 2000 hours should be expected out of a marine V8 that has had reasonable maintenance. 3000 hours isn't out of the question but I would consider that near worn out.

 

@ESPNSkier put the heads on and run it. The amount of labor saved in doing a complete teardown right now isn't that great. You could always yank it this winter if it bothers you.

 

[DW]

@ESPNSkier : as an FYI, the piston pin is offset in the piston. The purpose is to reduce piston slap specifically on cold start up, which you may hear from your #6 configuration. As noted, the combustion characteristics will not be ideal or same as others along with the potential of valve to head contact being much greater with mismatched piston orientation. I would do a clearance check (using clay) for 2 cylinders to compare valve to piston clearance on standard v. offending one. All the comments on tearing the bottom end apart are valid.

[ESPNSkier]

Good point @Mark_Matis, I did not think about that! Don't tell anyone but I haven't skied a tournament since the mid 80s. The funny/sad thing is that we have had one of the windiest springs that I can remember but it has been glass calm every day since the spark plug blew out....and it's driving me nuts!!!

[ESPNSkier]

10 days and $1,300 in parts later she is running again! I did not get to do a test run due to rain late yesterday but....no weird noises, no visible leaks and no sign of water in the oil after running in the boat house for about 30 minutes....hopefully, all is good! Had a scare when one of the new head bolts rung off while doing a final torque to 110 foot pounds. Replaced it with one of the old bolts and hope all is well.

[DW]

@ESPNSkier : I assume you mean rounded off the bolt head, not snapped one of the cylinder head bolts? One can be somewhat leery depending on where sourced of new hardware quality, many reports of defective hardware from off shore suppliers. Not parts you want on that airplane you are about to lift off terra firma on...

[oldjeep]

x2 I'd be a bit concerned with a head bolt that you could snap off with only 110 ft/lbs

[ESPNSkier]

@DW, no, I mean''t total bolt failure as one of the new 1/2" bolts snapped in the threads above the block. Fortunately it came out and I did not have to drill and tap it. The others torqued OK.

[oldjeep]

Keep an eye on them and consider re-torque after a few heat/cool cycles to make sure.

[ESPNSkier]

Thanks @oldjeep, that's my plan!

[DW]

@ESPNSkier : That means at least one of your new head bolts is defective assuming it was being torqued at the correct level. Your ease of extraction implies no issues with the block threads being an issue. Hopefully none of the others are defective although the probability exists others could be very close to failure if those are all from a single batch. As @oldjeep noted, keep an eye on them. When you were torqueing them, did you feel any weirdness or stretch as you closed in on the final torqueing sequence?

 

Did you get them from a reputable source? You might consider sending the broken one off for failure analysis and also getting the seller to pay for the check as they should not want to have a defective batch of cylinder head bolts.

[LeonL]

You know, I've rebuilt several engines of my own and always reused head bolts. I've raced drag cars and used head bolts over and over and over. Never had a failure.

[oldjeep]

As long as they are not torque to yield, I never replace them either. The newer torque to yield type are supposed to be replaced every time. Most newer Vortec truck engines use them, not sure on the marine engines but it seems pretty likely that they are.

 

Pretty sure an old 351 wouldn't have them

[ESPNSkier]

All of them felt fine through the final torque sequence with the exception of this one which felt a bit spongy until it snapped. I sent the bolt along with the Lot number back to the supplier. I would have just reused the old bolts but several were in bad shape. Yes @oldjeep, these are not the one-time use "torque-to-yield" bolts.