dragrcr1005

let me try to keep this as short as possible. I bought my boat in October 2012. after only using it three times in may of 2013 I had my first issue. as I was pulling into the marina the starboard motor shut off at idle. I tried to restart and would only start after cranking under full throttle leading me to believe that it was a carb issue(has twin hp500 carb motors) such as a stuck float. with some investigating after I realized it was not a fuel issue, I noticed the oil was over full but clean. I sucked the oil pan out and had water in the oil. thinking that I might have a gasket issue I did some quick rigging and plugging and put a pressure tester on the cooling system. I had a major leak. next I noticed that one of the headers was full of water from my pressure testing. I pulled all the spark plugs from that side of the motor and no water? after even more checking I had a cracked head. the crack was right above the exhaust seat on the #7 cyl. in the exhaust runner. my next thing was to buy new heads. trying to keep the motors the same, I bought the same dart iron eagles that were on it. when I did the work I noticed that the roller cam had a damaged lobe. not terrible but was going to need attention soon. at that point I decided to run the motor the way it was and pull it in the fall so I would not loose my whole summer with the boat. that brings me to the current problem. I noticed that toward the end of the year the motor was not running to good and had a miss at idle. I pulled the motor out and took it apart as planned. I noticed that the combustion chambers of both of the heads seemed excessively rusty. my thinking was to go thru the short block and do whatever it needed, replace the cam, and just check and clean the heads since I had just put them on 4 months prior. today I went to the machine shop and he showed me that all 8 exhaust seats were super rusted and pitted and would need to be replaced. also, the new high dollar Inconel ex valves I just bought were pitted and peeling on the stem and would need to be replaced. not what I was expecting. I pressure tested the hardin cyclone headers back in june and had no leaks. I need to do them again to make sure there isn't a problem there but I would think that if they were leaking then only one side would be leaking and not both but Im gonna pressure check them both in a few days to be sure. I have what I would consider to be the long risers and they have the exit at the very end of the riser so I don't see water coming all the way back up to the motor with those but maybe?. I checked the cam and I can not get any good numbers off of it to know the specs. since I am not trying to take the heads off of this motor in another 30 hours does anyone have any ideas of what would cause the seat and valve damage? the machine guy says water reversion but I wonder? I would have to agree because I cant see any other cause, but I am all ears and would love some other things to check while its all apart. since I do not know what is in the other motor and I could not identify the camshaft, I bought a crane 731. after doing some research on here I thought it would be the way to go. I only trying to do this rebuild once! thanks for any and all info anyone might have. thanks for reading!

FIXX

iTrader: (2)

usually that cam and gil manifolds revert water if the idle is to low..with you having a mis from one of the cylinders not firing that cylinder acts like a vacuum pump and will suck the water in the exhaust port..also if have your machinist check the rod length,,if you were sucking up and compressing water you could have bent a rod as well..you should have pulled both engine's,,if one is down the other usually is not far behind the other for a freshening..if your headers dont have turbulators in them you may want to consider getting some..they burn off excess moisture inside the tubes..

dragrcr1005

I had the turbolators installed. the rods checked ok. the port motor is a gen 6 and the starboard motor I am doing now is a gen 5. im guessing that the other motor is a much fresher engine just based on the condition of the outside of it.

Griff

I agree with your engine builder. Water reversion.
The 731 should not revert any water with Gil/Merc exhaust. The stock HP500 carb cam's reverted water because of the 110 lob sep.
Is there an MHP with a # scribed on the end of the cam????

FIXX

iTrader: (2)

correct,,it should not but it did??? drag,,like i mentioned if you had a misfireing cylinder at idle that cylinder will suck harder then a hooker on a friday night!

dragrcr1005

well not really, I haven't run the engine with the 731 cam to see if it reverts. I just purchased it to install in the new motor since the one that was in there was damaged. I have done a ton of reading on the stock cams but I cant find the mhp301 or 300 that is described on the forums . the cam that was removed was a cast hyd roller cam. the only numbers I can find is on the rear of the cam and reads as follows: "4603D494" I have not found any way to indentify it yet based on these numbers.

obnoxus

what do you idle at ?

500HP should be at 1000 rpm.

Personally I never set them that high because of shifting,,,,, but always bumped it up

Vinny P

So, you will be installing a new cam with a different profile in only 1 engine? How do you think the 2 engines will react with different cams?

MILD THUNDER

iTrader: (3)

Dart Iron eagles were not original HP500 heads. My guess, is if someone replaced the heads, they probably replaced the cams too. With what is the question. I'd be trying to figure out what cams you had in it. Who knows, they might be some stupid 108LSA car cams for all we know at this point.

With the 731 cams, everything magged and psi checked you should be fine. I will say though, for what you pay for a crane billet cam, Id be calling Bob Madera for a pair of his custom cams. The dart iron eagle is a pretty nice head, much better than a stock HP500 head. With the right cam, and a little more RPM, you can have some solid 575-600HP engines. I'd get a cam that will compliment the Dart heads. A lot of these off the shelf cams were ground based on the crappy GM exhaust port flow and IE ratio. The 10 degrees of added exhaust duration (226/236) is a bit much imo for a N/A with a decent flowing exhaust port. And I think i'd rather have the 114lsa over the 112. I am positive bob can design you a cam that will make more power, and be less reversion prone on that combo.

dragrcr1005

good point. this is my thinking. when I bought the boat it had a gen5(10 bolt cover) and a gen6(alum cover). the gen 6 had newer exhaust(per serial numbers from hardin), newer looking carb, and so on. my thinking was that it may have been a drop in or complete replacement. they don't look the same on the outside so whos to say they are the same on the inside? I have no way of knowing the condition of the engine or cam or any internals unless I tear it apart which I don't want to do. it might have the 731...who knows. the gen 6 has run perfect from day one. I have no way of knowing if someone took the time to build the motors exactly the same. sure doesn't look like it from the outside. lastly, if they perform different I will put the 731 in the other one. if you look at the profiles from the stock 500 to the 731 it is not that much different. doubt it will be noticed, but if so I will tear into my great running engine put the cam in it. I have been a mechanic for 19 years and a shop foreman for the last 10. I have become a firm believer that if it aint broke....don't fix it.