502 build
 

My 502 started losing oil psi and i found some metal in the oil filter when i cut it open so i feared the inevitable and pulled the motor. I will start by claiming i am NOT. A mechanic but i know a little and try to do what i can. I dropped the motor off to the builder and here is what i know so far. He hasnt gotten it torn down all the way yet but gave me a quick update

Gen 4 bowtie block
Eagle crank
Merlin heads ( said it looked like some port work had been done he was guessing 120cc but hadnt really got into yet)
Dish pistons (motor had a blower at one time) again he was guessing 8.5:1 compression?
Lunati rocker arms
Roller cam (doesnt have it out yet but will put it on the cam dr and find out what it is)
Dart intake
Holley carb ( not sure on specs yet)
Msd ign

He said he found a trail of rusty colored crap from 1 head bolt. That it possibly might be getting water in? The oil looks fine. Also the tray under the intake had some weird rusty looking crap. Other then that he thought the motor looked really good. Also said he saw some odd wearing at the top of the cyclinder walls didnt know if a normal hone would get it out?

He is suggesting rings/bearings and valve job at a minimum. Obviously i wanna keep it as cheap as possible but while its open if there is anything i can do to increase power without. Taking out a loan im all ears

I will know more next week after he gets it all tore down.


Just curious if you guys have any suggestions?

what's your end game? Same performance? Boost it? First you need to find out why it failed but it sounds like your mech is on top of it.

Ideally id like to make a little more but id be happy with the same i suspose. I want reliability more then anything. No blower for me. Would like to be in The 475-525 hp range without changing pistons (assuming old ones are fine)

Im guessing bearings are worn from the little ive done to it. (Lost oil psi at hot idle, bronze colored metal flakes in filter)

Builder said i saved myself some $ by pulling it when i did. Was still running great but i figured it was on borrowed time.

I'm no builder, but if the Pistons are good to go then new rings, bearings, rebuild and shave the heads a smidge, use the thinnest head gaskets available, find a better cam, and enjoy another thousand hours out of it.

If it has "dished" pistons in it, you're alot lower than 8.5:1. A merc 502 with a small "DOME" piston, is around 8.75:1.

Crane 731 (low to mid 500hp) -741 (mid - semi upper 500hp) with Lightning exhaust.

You may be correct. I thought he said dish but maybe it was dome. He did say it was somewhere around 8.5:1 compression just from looking at it. He said it had the stock rods as well which he thought was odd considering what else he had found but said it was ok for what we were doing. Again this all assuming everything is in good shape.

Ive got stainless marine exhaust. A new set of lightings isnt in the cards. I had them on my last velocity and they are pretty bad ass.

So one of my heads is cracked and isnt worth it to be fixed. Basically looking for a new set of heads. End result is im looking for about 600hp now. Cam isnt ordered as were waiting to decide on which way to go with heads

Any thoughts on a set of heads that wont break the bank?

Its no joke when someone tells you what what ever budget is to double it!

Set of EQ's and a Crane 741 will get you 600.

Will the crane 741 work with stainless marine exhaust? Does have long tails.

There have been a few engine builds here using the 741 with Stainless Marine's. One even had the RHS/Protopline heads, which is now the EQ heads.

I'll see if I can dig up the rest of the info...meaning, a link.

Works fine with my Gil silent choice exhaust

You lost me at "cheap as possible". Lol. However I do understand. Heads and 741 cam would wake it up pretty good. Other heads to look at that if you go that route also is profiler 320cc. They flow excellent out of the box with minimal clean up.

Trust me when i say nothing has been cheap on this project

My problem is i told my wife it was gonna be a simple refresh.....lol

Now its twice the estimated budget and every dollar spent from here on out is comming from a kitchen remodel budget that i have been promising for over a year

Im just trying to avoid her cutting me while im sleeping!

Welcome to the 99% 's.

Rule number one. Don't use credit card. Rule number two. Sleep with one eye open. Most women have no clue or understand what we have to do and in many cases want to do when it comes to this hobby. At least at this point you still have both your wife and your boat. I've had a couple that made me choose. Lol... Something about high octane and gunpowder that puts a big azz smile on my face.

Actually, some pretty good advice there. I had to re-employ the stash method of paying for boat related. I was just running into too many retaliatory purchases by my wife!

I really recommend you call the guru BM before doing anything, right Tim? LMAO

HAHA I just went thru this with my wife, she thought I said 800 last fall and what I really said was 8000. We atleast have separate accounts so that makes it some what easy.

Yep, if my wife found out how much my last build cost, she would be making the shoe store and the furniture store very happy!

Would he be able to make it to 600 with a set of AFR 265's and some Lightnings? The smaller chamber of the 265 would bump up the compression. I might actually be tearing into mine this fall, and if so, ya never know, might be a set of low hour ones going up for sale.

i might be interested in the 265s,let me know if you decide to sell them.

Definitely some smaller chamber heads would be ideal to bump the compression and make some good power gains at the same time. he'd really have to do some under the radar back alley trunk deal on those heads though. What chamber size are the oval 300's? List goes on. Then intake etc. $$$.

Assuming you have a dished piston, most "Dished" pistons in a bbc, are typically a -20cc dish. In a 502, with 119cc heads, you'd be looking at a static around 7.5:1 roughly. If you were to install say a 110cc chamber head on them, you'd be bumping it to a whopping 8:1.

If you're looking to build a decent pump gas engine combo, it sounds to me, like you're gonna need to change out those pistons.

Your absolutely right. For some reason I was thinking stock Pistons. Looks like a complete tear down regardless so OP gonna need Pistons along with whatever else builder finds. OP might wanna just do a rebuild with some machine work and new Pistons and refresh existing heads. Get compression up and do the 731 or 741 cam to keep it simple. Crank and cylinders ok? 2,500-3,000 when said and done.

Anybody see or even here of anyone running a dish in a 502 ?

Exactly.

I bet it doesn't.

We;ll see though,right.

Thanks guys. New pistons have already been ordered. I don't recall what he told me, but I believe it said it was a dome piston, and do remember he said compression would be between 9.25:1 -9.5:1. that was with him guessing, with the merlin heads (one of which is junk). So yea, the old pistons are not going back in. He did say my merlin heads had some pretty nice porting done to them, so he wanted to make sure we got something comparable to what I had.

I;m kinda surprised this motor ran as good as it did. One head had 2 different cracks (one of which had previously been repaired, which failed), the other crack ran through the head bolt area. The cam had a worn lobe.

block checked out ok, but he had concerns about piston to wall clearance, he said it would be over 7 thousandths, and wasn't keen on that. , Gen 4 bowtie block, with roller conversion. Block is getting bored .030. Crank polished.

600HP would get me solid 80mph GPS with this hull, at least it did with my 02 280.

He did say the motor looked like it was originally set up for a blower by the pistons, lower compression,, and cam grind. Which makes senses as the seller told me the boat originally had a blower, and he had it taken off. I'm guessing he literately unbolted the blower. I would have thought you would have to do some other tuning or something to make it run right, but the engine did run pretty good, I must admit. Had I never saw the oil psi issue, or cut open my filter I would have never known there was anything wrong with it.

I'll be talking to him tomorrow to figure out where to go from here. Just trying to do some homework in the mean time. Since I am gonna have to pony up for new heads, figure it kinda opened a door for a little more power.

600 is certainly achievable with a good head, cam, intake combo. Definitely plan on decent set of heads to get you there.

Heads, cam, intake combo and rebuild gonna getchur wife a lot of roses. Gonna be closer to 5-6k.

Maybe a little less. I forgot you had the dart intake. Make sure builder port matches intake.

I've been recently quoted 2-2500 for rebuilding short blocks with new pistons, etc. (I strip them and put the heads back on later)

EQ heads I believe I had $1400 in them with buying them bare and having a machine shop set them up. I'd have to pull recipes.

741 cam was $440

Gaskets were a few hundred along with longer ARP bolts due to heads.

I'd say budget for 5k and you should be fine. May get it done for 4k

Keep this thread going as you build it. I am looking at the same deal.

FYI, I am running a 502 with GM Alum 110cc 290 Oval Ports and a Dual Plane with 850QF. Isky cam very similar to 525EFI. 9.6:1. Runs really strong but I can't quite turn a 28 B1 fast enough so...

I am looking to build a 509 with a good set of Alum Rect. Port heads and make 600+. I want the 10:1 sound and fuel headache! I have a spare block and crank so might as well right?

As for the other issues, I'll ask my wife if I can buy a 30P B1. You have to let them see some things being bought, otherwise they get suspicious.

http://superboat.com/ open link go to downloads, page 40 of technical rules the 509 svl engine. i think in the race boat threads the svl guys are talking 630 640 hp range

He suggested promaxx heads. Bare unassembled and he will build em up. Said hes used em in past and they flow well and no issues although he admitted they do get a bad rap. I did some searching online and mostly good reviews for the $. Thinks i could be done with head work for $1500ish. Block is bored, crank was turned/ polished. Starting to blance the rotating assembly.

If on a tight budget, hands down i would go with a set of engine quest bbc iron heads, over those pro comp / promaxx chinese heads. Dont get lured into aluminum being superior to iron when it comes to performance. Even raw water cooled engines can corrode aluminum, throw in some cheap porous chinese castings, it could get bad.

Did this build ever happen? Updates?

His wife must have found out...

I don't even ask anymore. Easier to ask forgiveness.
That and Alzheimer's helps.

Lol. Yes it happened. Got the motor back in the boat in october. I got it on the water once before winter. I can tell its got more power but i never ran it over 4k. Rpms.

I am about $6100 into it. that includes a new quick fuel carb ($650). New set of promax heads bare that he assembled ($1500 ish). Custom ground roller cam. New pistons. I reused the crank (eagle), dart intake, ignition (msd). Motor wasnt dynod but he broke it in on his stand. I was there to verify. It sounds good, runs good but i only have 2 hrs on it so not much to go on yet. Overall ill be happy if it lasts.

Oh yea........wife thinks it cost $4000. She was more pissed about the 2200 i just spent on a tube swim platform then the motor