I posted this question in the general discussions area also, no need to answer twice.

I have a question for all you motor heads out there. I ran the boat for the first time last week end. Started fine, no noise, plenty of oil pressure, everything fine. I ran for about 2-3 hours and had to out run a thunderstorm to a marina. When I got in out of the rain, I checked things out and found oil in the bilge. Checked and I was a little low, looked like it came out the dip stick(?). Added some oil and started the motor and I had a low energy knock coming from the top and back of the motor. I idled it home and put it on the trailer. Got this feedback from the mechanic today.

Originally thought it was a fuel injector, nope.

Now, after talking to Mercury High Peformance, he thinks it is a roller follower on the cam, may need new cam shafts and roller rockers and exhaust valve springs. He says oil in the bilge was from a front seal leak on the drive (not there last fall when winterized).

He said that this cam/rocker problem is not unusual for the 1998-1999 HP500's with approximately 150 hours on them. Mine is a 1999 with 175 hours on it.

Anyone else have this problem?

"He said that this cam/rocker problem is not unusual for the 1998-1999 HP500's with approximately 150 hours on them. Mine is a 1999 with 175 hours on it."


Welcome to my world


I'm in the middle of a major rebuild catastrofic (sp) valve trane failure at a 160 hours. Don't use Crane springs! even their upgraded spring has too much seat pressure.

I don't know what to say about the oil I don't think guessing (the merc guy) is the right way to handle it. Start searching with a mirror or whatever it takes to find the leak. Slim chance but you might of run low enough on oil to cause some of the noise.

BTW my motors are 98 HP500 carbs but I think they used the same springs in 98 and 99. Good luck scott

Thanks for the reply Scott,

As far as the oil leak, it was dark oil in the bilge and since the boat only had a couple of hours on it from the last oil change that made me nervious also when I saw it. Could have been drive lube, said he found lube in the bellows and on the y tube (I have Silent Choice exhaust).

I'll ask about the Craine springs, he stated that they (Merc HP)changed the parts on newer engines and in the replacement parts. Don't know if they are still Craine, what are you using.

I hope I caught it early enough to limit damage, it was quiet when I put it in, so at most it knocked for only a couple of hours of running, most of it at around 3500rpm cruise speed or idle.

I'll be sure to post what I found out when we're done.

Here's the latest.

Mechanic can not find any visible signs of damage in the upper end. He talked to Merc HP and Bob Teague, both have said no problem with valve springs on the HP500EFI, it was a problem with the HP500 carberated engines.

Cams look fine and engine is clean (no metal shavings), replacing lifters should have the boat back by next weekend, will update after I run it.

Thanks for all the input and advise

This may not apply to your situation... One of my boats a 7.4 carbed had a noise much like a valve train or real slight rod knock. Couldnt pin point it other than it was from the rear of the engine. The begining of the next season still same noise only other thing I had noticed the prop spun by hand compaird to when I purchased the boat seemed different. Any way took it to a friend for inspection. He said everything was fine except forward thrust washer/bearing were bad and forward gear was close to exploding. He also ask me what lube I was running ...I said Amsoil ..he said no problem. He replaced forward gear and with a H/P one and guess what mistery noise is gone. I then remembered the guy that owned the boat before me did alot of tubing ski stuf then it made sense. He hammered out of the hole a bit too much.

turbo,

did the knock change whether you were in gear or not? Mine does not.

I would be in the yard running it with the muffs and hear it but since the drive was gone through its gone. Not saying its your problem but you never know and if the lifters dont fix it ?

Lastest update, knocking returned very quickly (matter of minutes on the water), mechanic took a compression check and found number 7 cylinder down to 40lbs. Pulled the head and found the number 7 piston burned.

Knocking now expected to have been carbon hitting the head.

No final cost yet, but expect it to be steep, and I have lost half my summer.

Hopefully it will be fixed (correctly this time) by this weekend.

Mama tryed, Kenny (aka Wheeler Dealer) and AeroBob thanks for all the rides in the last 6 weeks, with any luck I won't need them any more.

There are many questions as to why this was not found earlier, but live and learn.

For what it is worth, I have now also been told (second hand) that several HP500's have had the number 7 piston go south in our area.

What do you mean by burned?? Considering that you had 40 lbs of compression, I can assume that you don't have a hole in the top of the piston. Therefore I think that you mean the piston is burned around the edges. If that is the case, doesn't your mechanic think it could have been caused by a lean condition ie:an injector problem??? I would look for a cause before just replacing a piston and running it again. If it is a lean condition, the problem will return to haunt you again.

Can you post a picture of the piston?

Bad plug wires on number 5 and 7 cylinders could cause excessive advance in 7 and therefore detonation. This would result in "burnt piston" for #7. I would at minimum replace those two wires nd make sure they are well seperated on repaired motor.

BT