1986Scarab1

Offshore family,

Let me start by saying I absolutely love this board and have learned tons reading through these posts. This time, I'm in need of advice to clear up a few things on the motor build I'm working on for my 86 Scarab 1.

A little background:

1986, 21 foot Welcraft Scarab 1
260hp Mercruiser 5.7
Alpha 1

I bought the boat in great condition back in 2011. The motor had recently been rebuilt and ran like a top. I had various small issues over the seasons but never anything catastrophic. At the end of last season I noticed that the fiberglass around the motor mounts was cracking. Upon further inspection I decided to yank the engine, have the glass and wood checked/fixed underneath, and give the engine a bit more power.

The wood in the boat checked out good, I had new mounts installed and glassed in, and decided to plop some vortec heads on the old 350 while she was out of the boat. I also installed the correct vortec intake which mated up to my quadrajet (I believe) carb. The motor ran perfect.

Here comes the juicy part.. After having zero issues all summer on this setup and gaining a LOT of punch I noticed that I was leaking a bit of oil. I checked the dipstick and to my shock I was significantly low on oil. No knocking, no low oil pressure, no loss in performance but I had to add 2 full quarts to get back to full. I started the boat and rode the rest of the day keeping a close eye on oil pressure and checking the dipstick to make sure no crazy leaks. The boat didn't lose any oil the rest of the day.

I decided to leave my boat at the lake at a close friends dock for the evening since I was coming back the very next day. I head home, take my wife to a nice dinner and shortly after sitting down get a terrible text from my friend letting me know that he was out on the boat and the engine started to lose power, he pulled back to idle, shut the boat off, and checked the oil, still full.

Started the motor back up with engine hatch up and heard the dreaded knock dang.....

Oil pressure still normal, oil level normal, etc... He shut it down and had it towed back to his dock...

Of course I came to pick it up the next day and right back to my shop. I pulled the engine, pulled the motor apart and found 3 pistons broken, two at the rings and one at the skirt. Had the vortec heads I installed on the boat checked out, they're cracked and no good.

I think some of this was me running low on oil and not realizing it. I think most of it was detonation due to low octane gas (I know, I'm an idiot)... I've always run 87 in the boat with the old setup and it was perfectly fine, didn't even THINK for a moment about the added compression and running premium. Am I correct in assuming the low octane gas did it? Should I be running 93? 89?

Now, here is where I'm at with my new build:

-Block is good and will be honed before new parts go in (pistons, rings, crank, rods, bearings, etc..)
-Reman set of Vortecs ordered and will be delivered soon
-I want to put in a more aggressive cam for some additional power over stock cam I have in there now. As I understand it, in order to do so with the Vortec heads I have to either
A) convert to roller (sounds like more work and $$$ then I want to get into) or B) Order this spring kit which installs without any machining

https://www.alexsparts.com/valve-spr...ssure-vsk4h50/ and choose a cam that will work with this spring setup.

My questions:
1. What cam should I pick? Flat tappet style right? I know this boat will never be a speed demon with a 350/Alpha setup but I'd like to gain some MPH. I hardly go WOT but even when I do the boat will only turn 4200RPM currently with my 21 pitch Mirage Prop at 50MPH GPS. I think I need to pitch down to get more RPM and MPH out of my setup? The factory cam seems really tame for these sweet heads. I'm sure there is a cam available that will gain me power everywhere that will work with this setup and spring choice above? I want the cam to be noticeable from an exhaust note perspective but I don't want to sacrifice the boats manners either as I do always have family and guests on the boat, I need it to be reliable.

2. The spring kit I linked above should save me the trouble/cost of switching to a roller setup correct? The only other thing I would need to do other than order a cam that's compatible (flat tappet?) with my Gen 1 block and the spring setup is replace lifters, check pushrod length?

3. Is there anything I should do to the carburetor after installing the camshaft?

4. Will the Alpha hold up to the additional power? Vortec heads and a nice cam should put me in the 350 ish hp range I'd guess?

5. Should I upgrade rocker arms to 1.6 over the 1.5? Do they even make 1.6 for the vortec?

Thanks in advance for everyones input and sorry for the super long post. I just want to make sure that I'm making the right decision here before ordering any more parts for my build. I hope to put this motor together, gain some power and ride reliably for years to come. Please let me know if I'm missing anything or not thinking about something critical.

Cheers and happy boating!

Heath

dereknkathy

The lighter the boat, the better the alpha holds up. That 21 scarab will be ok with that. And spares are cheap and all over the place. Forged pistons.

1986Scarab1

I probably should have went forged. The kit I ordered did not come forged... Ugh, should I call the vendor and see if I can exchange? Just the pistons? Everything?

Also, for the cam, would these work together?

​​​​​​https://www.alexsparts.com/valve-spr...ssure-vsk4h50/

​​​​​​12-236-3 - Xtreme Marine?

Do I need any additional parts other than new lifters?

Thanks!

phragle

iTrader: (3)

Something was off from the beginning... Im not small block guy, but if it was 260 hp, and your heads etc made a good bump in power, then lets say your at 300 hp. with 300 hp a scarab one should see 60.

SB

iTrader: (1)

x 2 ! I

Scarab1 with stock 260hp should be close to mid 50's with proper prop.

Don't worry about that damned Alpha, Some of us abuse the crap out of them and laugh at the alpha haters.

1986Scarab1

The MPH drives me absolutely freaking nuts... I did have a 19 pitch prop when I had the original heads on (260 HP) configuration and she would run 49 MPH GPS around 4600 RPM or so WOT. Switched back to the 21 since the 19 was beaten up a bit when I popped the vortecs on and still saw only 50 MPH..

The boat doesn't miss a lick when floored, recent tune up, fresh plugs, wires, cap, rotor, etc..

Maybe the timing is off? Could it be that off though and still run so well?

SB

iTrader: (1)

Yes.

And remember, a rebuilt 350 can be anything. And a lot of times, not what you expected. Suks.

1986Scarab1

True, but the boat ran excellent and honestly didn't feel down on power. Would pop up on plane real hard and pull to its top speed quickly, just would hit a wall at 50 MPH..

airjunky

iTrader: (2)

Did the same thing on almost the same boat , should of seen 5k rpm with the 21
Vortec blocks are less than dirt cheap and the oem roller lifters will support the ht383 dirt cheap cam.,that works with stock springs and pressed in studs probably see valve float after 5 5200 rpm or so . That helps keep the alpha alive. Lives on 87 octane till the cows,come home.
I'm thinking you were lean or had some cold water hit some warm pistons , get the whole vortec motor cheap truck flywheel good head gasket job and hammer down

SB

iTrader: (1)

Let's get this out of the way, what elevation do you boat at ?