HP 500 Rebuild expertise
 

so last year I pulled my engine out to do a freshen up and came to the conclusion I would not be re boring the block due to corrosion and age. I than went ahead buying a brand New GM Block newest version (I believe Gen V1). the rebuild turned into almost a new build, we used new pistons, cam, roller rockers, lifters, intake, oil pump, timing chain , completely rebuilt original cast heads with new springs and valves etc, rebuilt carb... basically everything except crank and connecting rods. We built the motor to mirror the stock HP 500 merc with OEM parts, mostly since I was looking for reliability... I wanted the same motor package as I had before.

close to the end of the season I noticed I was slightly down on power ( maybe 25 hours max on new motor) and we found that I had reversion problem with some rusty valves and cylinder walls/rings, the exhaust and tails were new and pressure checked and not the cause of the problem. Fast forward this winter I have the motor at the machine shop totally apart for machine work and to put it back together. I plan on going with dry exhaust since reversion seems to be the only culprit. My question to the motor gurus out there would you put this motor back together with the stock OEM mercury racing cam that came with the HP500?

Do you have silent choice? Could the reversion be caused due to bad flappers?

I just hate putting engines back together stock so I'd bump the cam a little to the 741 provided your springs are ok with seat and open pressure. I would think they would but something to consider anyway. Just how much HP gain I'm not certain but I'd guess 25-30. Same cam in 525 hp efi I believe. Maybe some others have done the same thing am can chime in.

no silent choice , flappers were good,

[QUOTE=getrdunn;4526808]I just hate putting engines back together stock so I'd bump the cam a little to the 741 provided your springs are ok with seat and open pressure. I would think they would but something to consider anyway. Just how much HP gain I'm not certain but I'd guess 25

good point not sure if the 525 cam is direct swap , the 525 efi cam may have or may not have a gear for oil pump...not sure im explaining correctly but I remember hearing something along those lines, curious to hear more people chime in

HP 500 carb or efi? From what I understand the pre efi units were 110lsa while the efi units 114lsa

my motor is Carb NOT EFI

The 525 EFI cam has the distributor gear and is a 114 lsa, the 741 is same lift and duration on a 112 split according to Crane

110lsa then, as far as I know. "Almost" guaranteed reversion if that's the case depending on exhaust, valve timing, etc. I don't know why you got away with it on the first motor.

does that mean it will swap directly, does my HP500 have the gear as well?

If your using a gen 6 block your cam should be step nose ?? then they should swap, the cam gear spins the distributor shaft that the oil pump shaft seats in

exactly what I was thinking, last motor lasted 15+ years same spec

At least your going dry. Opens the door to more options regardless.

I'll take a very wild a** guess that the cam was degreed differently enough on the rebuild to be the critical difference? I have no practical experience on the matter.

What exhaust do you have? Newer style Gils with the hump or the older straight ones?

What cam is in it now, the exact hp500 cam or a similar cam? The hp500 cam was on a 110lsa and prone to reversion.

What is the idle speed? If it is set low and you idle a lot you may see reversion compared to a higher idle.

Just some thoughts/questions on your engine. I think the 500efi cam, or the 731 would be a good upgrade but of course opinions will vary on that.

i have two hp 500 efi engines in the shop,just finished one of them.all the big block chevy,s have a gear on the cam to turn the distributor&oil pump.as already stated,the hp 500 carbed engine has a lsa of 110 and is prone to reversion,the hp 500 efi has a cam with a lsa of 112 or 114,i can,t remember but it is a better choice.my question would be what has changed since the rebuild to allow reversion.

Wonder also if OP pressure tested manifolds. That could easily be the culprit.

maybe the replacement cam is not the same as the old one.do you have any paperwork on the new cam,also,what year was the old engine?

I wonder if he is referring to a fuel pump lobe instead of an oil pump gear???

By degrees differently do you mean different specd cam ?

Sorry to hear about your luck!

Mike's correct need to figure out what changed to prevent future problems.

Too bad you didn't start a thread sooner we could have twisted your arm into upgrading to EQ heads, wouldn't have cost much more with the sale of yours

I found the cam spec they used but can't post the pic of the spec does anyone have an email I can send it to and post it for me? Reading cam spec is like reading chinese to me

no doubt spent more rebuilding the gm heads than going with the eq,s.

t7p, ill pm you my email

Not to be a smart azz but I don't think he knew what he was trying to say. I would guess however he meant to say the cam could have been degreed by installing it advanced or retarded. Not 100% though. I would say it's more likely the builder may have picked out a cam close to but not exact with tighter lsa, etc. I've seen that happen a lot with engine builders that predominately do street and track builds. Just not marine savvy.

here you go

that does not look like a hp 500 cam.

Looks like this ?? no nose, but I think you can run this in a gen 6 with a button

http://www.ebay.com/itm/22223-Mellin...-/301990673099

Mike do you think the spec is different enough to have caused all my problems... What cam would you replace it with? Is 525 cam cool?, keep in mind I'm going dry exhaust

that sure is not a hp 500 carb cam,i don,t see all the specs so i can,t say for sure that is the problem but i would bet it is.is it a step nose or flat nose cam?

that sure is not a hp 500 carb cam,i don,t see all the specs so i can,t say for sure that is the problem but i would bet it is.is it a step nose or flat nose cam?169611 crane cam is what a hp 500 carbed engine came with.if you install one you won,t need to go with a dry exhaust,but the sound of dry exhaust is sweet ,until you get you,r first noise ticket.

that sure is not a hp 500 carb cam,i don,t see all the specs so i can,t say for sure that is the problem but i would bet it is.is it a step nose or flat nose cam?169611 crane cam is what a hp 500 carbed engine came with.if you install one you won,t need to go with a dry exhaust,but the sound of dry exhaust is sweet ,until you get you,r first noise ticket.cam cost 424.09 at summit.

i would get a hp 500 efi cam for the engine,it and you will be happier.

That cam posted is a 502/415 hp mpi cam isn't it.

if it is it was installed wrong,the 415/502 cam is not a reverter.

Not to hijack here but have a quick question and don't think I have seen a cam thread in some time.....

I have 500efis with top ends done not long ago let's say 50 hours. Could I swap the 500 cams for 525 efi cams with out changing any thing else? Or will some changes to springs and such be needed as well?

here u go. Sure exhaust isn't cracked?

yes.it may need a computer reflash.