HP 500 EFI head gasket failure
 

Bad timing, in the heart of the summer. I was trying to go as slow as the boat would go on plane, about 2800rpm and it suddenly lost power and started falling off plane. I pushed the sticks forward, lowered the drives and it struggled back up on plane. Was close to destination, backed down the engines and no waked for about 5min, parked all day. port engine sounded funny on start up but boat ran up to 3500 cruise for 7 miles home. Next day port was popping and not wanting to rev. loaded it and took it home thinking bad gas(I wish) or something. Plugs were sooty 4,6,8 were wet. Comp test was spot on 1 3 5 7 and 2, 4 6and 8 had 20psi or less. Leak down revealed leakage between those cylinders. It being summer, I knew there was no way to get any serious issues fixed in time, so I opted to take a peak with the engine in the boat(oh my aching back). Head gasket was melted between cylinders 8 6 and 4, #6 piston and CC were clean, 4 and 8 looked normal. After cleaning everything up, I may get lucky and can salvage the summer. My question is why was 6 washed? did the gasket blow in the 2 spots and then the adjacent cylinders fuel plus its own fuel make everything clean? or did something happened in 6 causing it to blow into the 2 adjacent cylinders. Heres some additional info. I tested fuel pressure while diagnosing the fouled plug issue 38-40 on prime, idle and as much easy rpms as i could give it. I left the gauge on it( they could have put that shrader in an easier spot) and 2 days later it was still holding 25psi, when i pulled the intake. The Boat is a 2000 Baja 342, the HP500EFIs have 688hrs. This port engine still had the factory seal on the front intake bolt( had to cut the wire). I bought the boat with 603hrs and did valve springs before I ever started it the first time. I have meticulously maintained it for the going on 4 years i have owned it, including a mid season oil change and compression test/plug change every season. I am hoping it is just age, but if there is anyone who has had a similar issue and knows the cause, I would be thankful for the info.
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That type of damage can be caused by detonation. Might not be a bad idea to have the injectors cleaned and flow checked.

Personally if it was mine there is no way I would have it pulled down that far and not do the other side too.

Well this is a temporary fix, to hopefully get thru the summer. the compression test on the other side was identical to the one I did pre season. If I had intended to do both sides I would definitely pull the engine, and if your gonna pull one might as well pull the other, and if you got them out might as well do rings and bearings and so on. You guys that do this all the time in the boats are complete animals! Im 58 and this will be the last time lol. I was actually planning to do them this winter. Of course I was planning on last winter too lol.

Mission Creep is an issue at the best of times...it's a nightmare when you actually find more things that need doing...lol.

In this case, I think the suggestion of checking the other head/gasket would be the prudent thing to do. Wouldn't take long...and maybe it was on the way out too...and that would dampen the summer x2.

Do the other side too. If you don’t it will bite you in the ass at some point. If you take it apart and it all looks good at least you can sleep better at night knowing you did the right thing. Really, what’s it gonna take, maybe another hour of your time and another head gasket cost? Good luck. :D

I assume those are stock un opened. It was a somewhat common problem if I remember correctly. Like other said do both sides and if you have not did springs and seats, do them now.

I understand you want to get back out but a failure on those and you will have bigger issues.

If you pull the other head, I’ll bet you find the gasket looking like charcoal
in the adjacent cylinder area….this isn’t uncommon with these, you probably got more hours than most

while you’re in there, might want to pull the lifters and check the condition of
the rollers

Shotgunn,

One word.... Cometic. :ernaehrung004:

Thanks. Brad.

Ok sheese, We may need to start a go fund me for my back surgery. I will pull the other head Saturday. Thank you guys for your inputs and convincing me to do the right thing. Hopefully I'll be relaxing(recovering) on the sunpad in Party Cove next weekend. The charcoal thing was pretty convincing lol.

Glad I did the other side! Thanks
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Aluminum heads on BBCs have many benefits...

Be grateful you have the room to do some surgery...I would have to pull the engine to pull the heads. Even get the exh manifolds off.

Glad you were able to get more data on how the stb head gasket failed.

As Brad said...worth just having a look at rhe rollers on the lifters and the cam lobes.

Tartilla,

I’d love to take credit, but that was JayTee.

But I do stand my my Cometic recommendation.

Thanks. Brad.

I did peek at the rollers. The main reason I bought this boat was the HUGE engine room, but I never planned on pulling the heads in there. I have extension boxes so I dont even need to pull the drives to get the engines out. Im gonna try to remember to fix the float switch before I put the exhaust back on. I dropped 2 bolts(stainless of course) and was able to simply reach down and retrieve them. I sure hope this works out, I really do prefer being on the lake rather than being in this engine room.

I bought a telescoping magnetic pick-up tool to keep on the boat....but .ost of my hardware is stainless....lol...so it mostly gets used for the odd socket that migrates to the bilge.

I have two of these.(they fo make a much longer one too ) . Super soft aluminium. Will bend into any shape.
I broke off the magnet off one. I bend the end into a U. Size depending on objectvtrying to get. It lets me pull things forward on floor of boat under engine without getting stuck on other metal things .

Now that you’ve schooled in doing these, you should probably plan on doing
its neighbor to the right….. I’ll bet they’re in the same condition as the head you last removed

Next time they are getting pulled lol. The other one had a top end done before I got it. The little wire lock through the intake bolt is missing and the head gasket looks different. I am unsure exactly when but was told it was recent(by the salesman, so you know its true). I am planning to yank them this winter and turn them into 509s. The boat runs plenty good so maybe just a bit of head and intake work and a better tune, and hopefully all set for another 600hrs. Maybe my next life I'll get my staggered Top Gun with some serious power, but this go round I'm a Baja baby. I really do like these HP500EFIs, the boat is pretty solid with all the luxuries you could ever want, a pretty good starter boat into a realm I wish I'd gotten into years ago.

How’s the block deck under that really bad gasket?

it was fine, cleaned it up and put a straight edge on it. I will work on it in the evenings and hopefully find out by this weekend.

2 down. 2 to go.

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Toogoodtobetrue?
Is this right? Part number says it fits HP500EFI are they counterfeit? is there a better option?

Hopefully Smitty ( Articfriends ) on here will see this, he is the King of injectors........If you're buying injectors for 10 bucks a piece they are junk.

Thats what I was thinking. Who makes the oem mercury injectors?

First off why do you think you need new injectors ? Ive sent several sets over the years to Smitty who has cleaned, flow tested, new parts if needed and new O rings.........send him a PM

If they are stock 500 efi injectors they are no longer made

Smitty may still have my old stock 500 efi injectors if you need some I replaced all mine when I did rebuilds this summer.

So I wastn't sure what was wrong when this first happened and was searching a lot of stuff including new injectors. So now almost 2 weeks later, all my feeds and emails and weather pages are full of injectors lol. these just popped up somewhere this morning, and I saw the 8X and thought that has to be a typo...
I will definitely send them off(hopefully to Smitty) this winter to have them checked/fixed.

To read on 500 FI injectors Artic friends did a lot of threads on this period even the 496 Guru guy that said he came up with a perfect matching side of 500 if I injectors, they fell short just because something is rated at the same flow at the same pressure as what they’re replacing does not actually mean may perform the same this a lot more than those two numbers.

to date there is no replacement injector thats a dead match, the 500 efi has tiny injctors flow wise for its power level at 36 lbs. The 42 lbs you found flow more at static and most likely less at lighter settings on top of fact they are chinese junk and wont flow real great overall at 10$ a piece retail, lmk if you need yours flowed and checked, Smitty

So is there any solution if an injector goes bad? Or is the only thing to do replace all and retune?

Wildman, others...

The injectors for the 496 are 43lb/hr, right? Are they comparable, dimensionally?

Thanks. Brad.

There are plenty of injectors, I may not have been clear. Is there any that will not require a retune to the ECU?

All done, timing set at 8* in service mode. tested total in normal mode at 36*. Ran it yesterday and all's well ! Hopefully a great rest of the Summer, Thanks for all the input
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Great to see you back up and running! I’m one of the few others that also have a 342 with factory 500EFIs, it’s a nice running boat with those motors. I’m approaching the first valvetrain service, this has convinced me to go full shot with heads off and new headgaskets.

Those heads are heavy! Do you have extension boxes too?

Oh I know, I’ve built several big block motors! No extension boxes on mine.

They are even heavier trying to haul them in and out of the boat lol. What is your top speed? I'm curios what the boxes are worth.

Yeah, that’s got me thinking pull the motors when it’s time. I was going to just do the springs, retainers, etc and fresh rockers without pulling the heads because both engines still have all of the factory cable seals and I didn’t want to break them. But fresh headgaskets would give me way more confidence after seeing your situation.

I’m at 74-76mph on gps. 74 right now with 30P B1 props at 4,600 RPMs. I have the original 28P B1 props that had been cut down a bit, those were 76 at about 5,000 RPM. The 28’s would blow out easily getting on plane, 30’s are much better. I also get really good cruise speed and good efficiency with the 30’s. 2,750 RPMs is 40mph at 1.6 mpg, which is where most of my runtime is. Lab finishing the 30’s is the plan - at some point, lol.

How about you? I’m very curious about the extension boxes.

I have the cut down 28s, when they were fresh back from the lab I was at 80gps @5200, the props held very well. I am always gentle with the sticks when planing, cause of the bravo1 drives. I caught a log last year and dinged up both props, I fixed them myself cause I didnt want to spend another 1000.00 plus 2 weekends out. It hasnt run past 76 since. I was considering 30s after I do rebuilds on the engines. I cant cruise under 3000 and 3400 seems like the sweet spot at 50mph. I rarely take it to full throttle anymore mostly because of the hours.

I am also no genny and no AC, but everything else including a 50lb box anchor setup in my modified anchor locker. Shes a bit porky, but definitely rides nice on my wakeboat, mini yacht infested lake lol.

That’s solid speed for our boats! I haven’t been running it hard because I’m worried about the original injectors suddenly going lean and causing a catastrophic failure. I just bought a spare set from another OSO member that articfriends had recently cleaned. I’ll put them in when I have the time and send my originals out to him to be cleaned/flowed.

I’m also no AC/genny.

Enjoy it and have a great season!