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My winter project was to re-vitalize my 1997 version carbed HP500 for my Boat. I really wanted to just freshen it up, but that fantasy didn't last long. It quickly turned into a full build-up. Not a big HP blower motor or anything like that, but (IMO) a solid build for a big heavy lake boat (on a budget) :D

Here it is in a nutshell;


8.9:1, .030 over 502 GM block (Gen V). Bored and honed with Plates, plateau honed, square decked .015 - .019. Align bored. GM forged crank, micro polished only. Dimple rods, resized and shot peened. SRP 4.500 -3cc dome pistons, JE rings. Pistons are .005 in the hole. Melling HV 1077 pump, standard press. Changed bypass valve to 30# in block and remote pad

Heads are stock 088 castings. I did an extensive bowl blend and opened up SS radius, polished the chambers, 5 angle int, full radius exh, 122 cc chambers (thanks Merc), Milled .010, .100 longer valves with 11/32 stems (REV's), 2.25 int, 1.88 ex. Flowed 358 @ .700. Morel lifters, Crane gold rockers

Dart intake (HP500), Gil exhaust, 800 cfm Holley, MSD ignition system.

Straub Hyd Roller (Squishy :D) 650/603, 228/242.

Made 544 @ 5700, 570 tq @ 4100... 510tq @ 3000.

Comes out of the hole like a rocket and accelerates a lot harder than expected. Still haven't pushed any top speed, but got it to 75 with 5 people and 80 gallons of fuel in it. I imagine I can get close to 80 if I work at it, and lighten it up. After I put some more time on it ;)

Chris gave me a lot of good advice, and supplied a lot of the parts for my build, and I'm a very happy customer. Thanks again for all your help Chris.

Dave
 

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steelcomp was here
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Sounds like a good job. Is this an I/O? Can't be...Chris has no idea what he's doing when it comes to those deals.;)
 

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Discussion Starter #3 (Edited)
Sounds like a good job. Is this an I/O? Can't be...Chris has no idea what he's doing when it comes to those deals.;)
HAAA!! In that Tennesee accent of his, " You mean it's got one of them outdrive deals on the back with the prop on it?"
 

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Dave,
No thank you for letting me be a part of the project. I think I go Stephen on the straight and narrow now and he should be happy with camshaft.
 

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Dave,
No thank you for letting me be a part of the project. I think I go Stephen on the straight and narrow now and he should be happy with camshaft.
Boy I hope so. I'm tired of towing his azz every year. 3 years, 3 motors. Unfortunately I think the cam is only part of his problem. Just sent me a picture of a plug that's missing the center electrode :))eek:)), AND he's wondering why the rocker arms move back and forth across the valve and retainer about 1/2" . Is it a bad thing when the heel of the rocker almost touches the Guide plates when on the seat :)hammers Maybe the pushrods are too short Steve!! :D
 

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steelcomp was here
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Boy I hope so. I'm tired of towing his azz every year. 3 years, 3 motors. Unfortunately I think the cam is only part of his problem. Just sent me a picture of a plug that's missing the center electrode :))eek:)), AND he's wondering why the rocker arms move back and forth across the valve and retainer about 1/2" . Is it a bad thing when the heel of the rocker almost touches the Guide plates when on the seat :)hammers Maybe the pushrods are too short Steve!! :D
Yeah, but I bet the roller is in the center of the valve...:)sphss
:)hand
 

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In the interest of helping the OP only, I am going to post in a thread I would normally stay as far away as possible.

Someone mentioned something about getting info from someone who builds Sterndrive engines, and it was mentioned many times about experience with the HP 500.

I do both for a living and have a lot of experience with both.

The failure is not from reversion. Reversion is not selective to cylinders or one bank of an engine. Although the HP 500 risers, especially if they are the short ones for silent choice, are prone to reversion, that is a separate issue from this failure. The exhaust seat came out. Period. Not from water. The water came from the exhaust valve not seating and therefore making that cylinder a reverse water pump. Those pictures show absolutely NO evidence of water reversion from the beginning. Anyone with real reversion experience can see that.

It also is not possible to force water past the impeller in the driveway. Especially with "ear muffs". You can put all the pressure a hose can supply by clamping the pickup hose over the garden hose and it still will not get past the impeller. And if it could, then what? The water entering the exhaust in the tail pipe is free flowing down the pipe and out the transom. At this point, the only possibility of water entering the cylinder is because of reversion, not water pressure. I only talk about this to keep the OP looking in the right direction.

Water intrusion COULD have caused the seat to come out. It would be from something like shutting a hot engine off in the lake. It runs backward for even a half revolution, filling that cylinder. Compromises the exhaust valve and seat, eventually failing. Just one possibility. I, believe it is more along the lines of that cylinder detonating.

During the rebuild, were any of the seats replaced?

The failure has nothing to do with the camshaft.
 

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Discussion Starter #11
Chris Straub,

Don't be shy... I know your reading this.
 

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BD

None of the seats were replaced. All original, Both heads were crack checked, and pressure tested after new guides.

The engine was never opened up prior to this re-build. Lock wires were still on the crank pulley, and the Intake manifold.

And yes, it has the short risers, and yes I tried calling you the other day about extending them for me, but no answer. I'll call later......

Dave
 

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BD

None of the seats were replaced. All original, Both heads were crack checked, and pressure tested after new guides.

The engine was never opened up prior to this re-build. Lock wires were still on the crank pulley, and the Intake manifold.

And yes, it has the short risers, and yes I tried calling you the other day about extending them for me, but no answer. I'll call later......

Dave
Sorry about the no answer. For some reason if we are on the phone, it is not rolling over to vm. If it was last week, we were at the boat show.
 

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Chris Straub,

Don't be shy... I know your reading this.
I was made aware of this thread right before lunch. I had a lunch meeting and I am back in the office. First I apologize to the OP for Tara/User/Sutphen30/Duke...hell i have forgot them all that he post under. His personal feelings for me leads threads into the trash.

The seat duration on this cam along with the lobe sep puts the overlap at 6 degrees less then what Mercury had on the reversion prone HP500s. In fact is the same as a 415 Mag 502. If reversion had been the issue you would have never gotten 40hours out of the engine.

The seat dropping out of GM heads on BBC in marine applications is well documented. From 330HP 454's to performance 502 platform engines.

Call me and let me know what I can do. I hate it when anyone has bad luck like this.
 

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The failure is not from reversion. Reversion is not selective to cylinders or one bank of an engine. Although the HP 500 risers, especially if they are the short ones for silent choice, are prone to reversion, that is a separate issue from this failure. The exhaust seat came out. Period. Not from water. The water came from the exhaust valve not seating and therefore making that cylinder a reverse water pump. Those pictures show absolutely NO evidence of water reversion from the beginning. Anyone with real reversion experience can see that.

It also is not possible to force water past the impeller in the driveway. Especially with "ear muffs". You can put all the pressure a hose can supply by clamping the pickup hose over the garden hose and it still will not get past the impeller. And if it could, then what? The water entering the exhaust in the tail pipe is free flowing down the pipe and out the transom. At this point, the only possibility of water entering the cylinder is because of reversion, not water pressure. I only talk about this to keep the OP looking in the right direction.

Water intrusion COULD have caused the seat to come out. It would be from something like shutting a hot engine off in the lake. It runs backward for even a half revolution, filling that cylinder. Compromises the exhaust valve and seat, eventually failing. Just one possibility. I, believe it is more along the lines of that cylinder detonating.

The failure has nothing to do with the camshaft.
That right there is BY FAR the most reasonable explaintion on this thread. Seriously ashamed I didn't think of it myself. With no exhaust seat the cylinder was free to suck water out of the exhaust during the entire intake stroke. Specially during closed throttle high vacuum ideing.


The whole idea about the garden hose in the drive way thing is not knowing the attitude of the boat and the angle of the exhaust. On the water this is pretty much a a given. Attached to the back of a truck, not so much.
I will agree it is almost impossible to force water passed the impellor with a set of muffs. With a direct hose connection, I've done it to a Merc raw water pump many times. It just takes time to fill the entire system, but it will do it. Your 100% correct, all it can do is exit the exhaust and it cannot fill a cylinder. But is the engine is cranked, not lit, and the bow is down enough, its much more likely to see reversion than a running engine. specially on the water.

My whole point here Brian was that if you have an deal on the edge of reversion, you need to be extra carefull in the driveway. Nothing more.

But hands down Brian, your explaination of events is dead on. Great diagnosis!:))THumbsUp Just matter of what caused the seat to pop. Sadly, shit happens. Wouldn't be the first seat that ever failed.



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Much of thread removed.

Stop the arguing and fighting on our forums.

Questions, read dyno rules.

Still have questions, read them again. admin3
 

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I'm opening this thread to add something constructive.

I did not read any of the mud slinging.... but think it might have something to do wiith a seat coming out and water.

I have found on Merc marine heads exhaust guides corroded inside the water jacket. Cannot see it only by pressure test. That would let water in and quench a seat.

Closed once again.
 
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