1970 chevy 250 inline 6 yet another post!!

[70Silverline]

ok so we figured out the problem from my first thread i sputtered out on the river aha the problem a bad thermostat stuck in CLOSED position OUCH dang near fried the motor compression is still reading good however i now have a very slight blow by on the rings ok heres the new quistion....

i am going to start to take this motor apart bit by bit to make it lighter since im working with scaffolding and a 5000 lb chain lift the lift aint my worried the scaffolding only holds 1000 lbs im afraid it might give way and tear a huge hole in my boat lol anyways im gonna take it apart and pull the block out and rebuild this entire engine with my dads 30 + yrs help in automotive engine building however what needs to come off before we take out the block does the outdrive need to be taken off?

if i do need to take the outdrive off what else should i replace now granted the boat is 39 years old and god only knows last time bellows were replaced and there dry rotted now!!

i will be building this engine in a machine shop with very high performance parts hopefully to gain another 150 hp can my outdrive take this pressure or should i beef it up somehow?

just to recap motor is coming out what else needs to come off before motor can be pulled?

motor will be all high performance (racing) engine parts so going from about 140-165 hp to about 250-275 hp probably (will be dynoed with paperwork and blueprinted engine) so does my outdrive need a beefing and rebuild as well or just few new parts and paint?

 

[70Silverline]

Re: 1970 chevy 250 inline 6 yet another post!!

also just to add ALL WIRING to be taken out i got all diagrams just to add that as well because im redoing floors, seats, all holes filled and redone and repainting as well might as well pull outdrive then huh?

 

[sutherj]

Re: 1970 chevy 250 inline 6 yet another post!!

I've got a 72 inline 6. I've had t out a couple of times. I don't think you need to mess with the outdrive unless you want to. I would suggest taking one project at a time and do the motor first. If the outdrive is good leave it be. I bought another boat a year ago to scavange some parts. I pulled the motor and outdrive out of it and junked the boat. The outdrive comes out easy enough but if it's not a problem I'd leave it alone. Those outdrives were in a lot of v8 boats. I'm sure it can handle the new HP.

 

[ziggy]

Re: 1970 chevy 250 inline 6 yet another post!!

start by reading your service manual. the part that says removal/installation section. you'll find your answers there.

yes, you remove the drive 1st. you remove everything that's connected to the engine in any way shape or form. then remove the engine.

i'm not aware of any marine gearhead parts for a 165hp mercrusier/chevy 250.

i'd suggest you build it by the mercruiser service manual and have a nice reliable 165hp L6 when your done.

and do the pm to your drive while you've got it off too...

 

[70Silverline]

Re: 1970 chevy 250 inline 6 yet another post!!

i have found ALOT of performance parts for this motor such as cam head (this has intergrated head so im doing away with that) also going to through the hull exauhst for a kick (*****) sound and doing away with through the prop also gonna TRY to change this over to fully self conatined liquid cooled with radiator just wondering about how to cool the outdrive like that im gonna fully restore the boat to factory and better with my brother(hes a painter) hes gonna do a 4 layer graphics flame job on it and the new name for the boat is KICKN UR BASS due to the lightweight and small boat config and the hp ratings i have seen some inline 6's get 650 HP out of them at the track so im sure theres a way to make it much much more heavy duty and faster i want at least 65 MPH out of this boat i may even go with a 4.3 liter and do away with the 4.1 any thoughts on that i KNOW there are a ton of performance parts for that motor i got one in my 97 gmc jimy and has a ton of power will break wheels if im not careful in 4 wheel drive!!

 

[70Silverline]

Re: 1970 chevy 250 inline 6 yet another post!!

another quick quistion since the boat is 39 yrs old how much would a full rebuild and reconstruction of the outdrive run me approximatly to inlcude all new bearings and all new gears and dont forget the badd wicked paint job on the boat dont want the outdrive all dull and ugly!!


just a estimate i dont do outdrives motors and wiring i can handle lol

 

[fishrdan]

Re: 1970 chevy 250 inline 6 yet another post!!

Yup, read up on the service manuals as Ziggy said.

When everything is apart you are going to want to replace the bellows, gimble bearing, lower shift cable, etc..

I think your goal of adding a 100HP to a marine 165HP L6 engine is unrealistic,,, if not impossible. Bump the compression and you can get detonation. Put in an aggressive cam and you can suck water into the engine. Boring won't get much added power. Chevy did make a 292 L6, so I guess you could probably stroke the engine using OEM GM parts and that would net some decent power. Kind of like the Mercruiser 140HP being a stroked version of the 120HP, 181CI vs 153CI).

But really, you should aim to build a reliable engine that will be able to run at max RPM for hours on end, balancing the rotating assembly, porting/polishing the head, gasket matching manifold, performance valve job,,, things that will add to performance while not hampering the engine's reliability.

 

[CheapboatKev]

Re: 1970 chevy 250 inline 6 yet another post!!

No way you are going to add 150 ponies to that straight 6...Do not confuse automotive builds that can get very impressive HP numbers with this marine motor...

Your gearing in the OD couldnt keep up with the engine...

Reliability is the trademark of the I6..You want big HP, find a way to stuff a big V8 in there with a Bravo OD...

 

[Bondo]

Re: 1970 chevy 250 inline 6 yet another post!!

i have found ALOT of performance parts for this motor such as cam head (this has intergrated head so im doing away with that) also going to through the hull exauhst for a kick (*****) sound and doing away with through the prop also gonna TRY to change this over to fully self conatined liquid cooled with radiator just wondering about how to cool the outdrive like that im gonna fully restore the boat to factory and better with my brother(hes a painter) hes gonna do a 4 layer graphics flame job on it and the new name for the boat is KICKN UR BASS due to the lightweight and small boat config and the hp ratings i have seen some inline 6's get 650 HP out of them at the track so im sure theres a way to make it much much more heavy duty and faster i want at least 65 MPH out of this boat i may even go with a 4.3 liter and do away with the 4.1 any thoughts on that i KNOW there are a ton of performance parts for that motor i got one in my 97 gmc jimy and has a ton of power will break wheels if im not careful in 4 wheel drive!!

Ayuh,.... Your Dreamin'.... It's a Boat motor, not a Race motor...

Come on back when you Wake Up,......

 

[70Silverline]

Re: 1970 chevy 250 inline 6 yet another post!!

ok just thought about what someone on here said and with a mild cam it shouldnt suck in water and just a .40 over or stroke it out and balance everything and port polish heads and custom valve job should run me about 900 all togather i checked on a few prices this morning just the dang head is gonna cost me 500 of it lol anyways you guys are right im thinking street truck and not marine engine im thinking about building a state of art L6 with all new upgrades like electronic ignition for one lol going with maybe mallory ignition or msd changeover the points which i hate!!

with a 170-180 hp coming from the engine and the short 16 and 1/2 foot stance of the boat equipped with a tri hull and a new paint job hopefully can get the boat to 55 or 60 tops with one rider

 

[cnr2003]

Re: 1970 chevy 250 inline 6 yet another post!!

Why not just throw a supercharger on there? Several of the hot rodders have installed the eaton blower off the 3.8L engine in their cars with little modifications. If you build the internals to be reliable and you did figure out a radiated cooling system, you wouldn't have to worry about extra heat generated by the blower. Plus this would bump up your hp to your desired range.

 

[IVAZ]

Re: 1970 chevy 250 inline 6 yet another post!!

You are not going to go 55 or 60 mph in that boat with the L6.
My dad "hot rods" those straight sixes on cars but we figured out it was not really feasible in marine applications. Intake and exhaust manifolds are going to limit your speed dreams.
Those engines are very tough reliable machines. Rebuild it to factory specs and enjoy it. My other boat had one and I enjoyed it. I even trashed the timing gears and was able to repair it and have it run good again (with iboaters help). My buddy bought that boat from me and is currently running it every weekend.

 

[ziggy]

Re: 1970 chevy 250 inline 6 yet another post!!

changeover the points which i hate!!

you must not have a dwell meter. points ain't that hard to set. i dwell and timed mine yesterday after removing the distributor to repair an oil leak on the fore pushrod cover. took me more time to go get and to hook up the dwell meter and timing light than it took to set them both.. points type systems have worked well for years and you gain nothing that i'm aware of performance wise by going electronic ign. you do gain that you never have to set dwell again. but like i said, setting dwell ain't that hard to accomplish...

there just don't seem to be much you can do to the 4.1L L6 to make it any more than it is. in the marine environment. get used to this idea and devote your time to setting your engine up to mercruiser specs. and it'll treat you kindly for years to come... me personally. my goal for my L6 is to have it run as good as my buddies 08, v6, 220hp fuelie. and his runs like brand new which it was last year. so my bar is high for my goal.. like i said. get used to the idea that the L6 will never be anything more than they are. which is a very good, long lasting marine duty engine. if you treat them right...

 

[Bondo]

Re: 1970 chevy 250 inline 6 yet another post!!

and you did figure out a radiated cooling system, you wouldn't have to worry about extra heat generated by the blower.

??????

 

[IVAZ]

Re: 1970 chevy 250 inline 6 yet another post!!

Why not just throw a supercharger on there? Several of the hot rodders have installed the eaton blower off the 3.8L engine in their cars with little modifications. If you build the internals to be reliable and you did figure out a radiated cooling system, you wouldn't have to worry about extra heat generated by the blower. Plus this would bump up your hp to your desired range.

He is not going to easily or reasonably figure out the radiator issue. It would be best to sell that boat and start with one that has a 350 or 454 and take it from there. I bet it would even be cheaper that way.

 

[cnr2003]

Re: 1970 chevy 250 inline 6 yet another post!!

??????

I was referring to heat in the engine bay. If he already had a custom radiator he could just plumb in an intercooler. That would keep the supercharger cooled.

 

[Bondo]

Re: 1970 chevy 250 inline 6 yet another post!!

Ayuh,...

And why would you put a radiator in a boat that surrounded by Millions of gallons of Cold water,..??

 

[cnr2003]

Re: 1970 chevy 250 inline 6 yet another post!!

Ayuh,...

And why would you put a radiator in a boat that surrounded by Millions of gallons of Cold water,..??

I'm not saying I would. Mercruiser did it with one of their 4-bangers didn't they?

Anyways, I would definitely like to see the engine built up. It may be a reliable motor as is, but anytime I replace something I try to upgrade. If he's going to tear it down, why not build it better?

At the very least, a little porting of the head and maybe an upgraded carb would probably wake this old motor up.

 

[70Silverline]

Re: 1970 chevy 250 inline 6 yet another post!!

hey just out of curiousity i began tearing it down today and found my motor is perfect i ran a comp check with WOT and hitting 149 almost 150 on the nose all cylinder i pulled the head and everything and dang does it look nice in there i bielive the motor was rebuilt some time ago but i dunno my quistion is i have gas on my brand new plugs? lots of gas? i can see and smell it there not dry? is it the carb not set correctly i just had it rebuilt is why im asking wanna use it again maybe get a bigger better one dunno yet or sell it as a rebuilt model?

 

[70Silverline]

Re: 1970 chevy 250 inline 6 yet another post!!

heres a short list of the upgrades.... SO FAR anyway

new cam
port polish magnaflux clean and shave heads and high performance valves
new rings oversized ofcourse probably .40 over
new pistons
ofcourse bored and honed
new lifters
rods
bearings
total new motor paint job
all new marine seals and gaskets
new oil pump( double pumper for double flow )
new marine grade timing set
MAYBE new 2 barrel carb instead of old 1 barrel
new riser due to adding captains choice switch for exaust
new chrome exauhst housing for the rear
new sterring cables and throttle cables
new bilge pumps (2 of them at 500 a piece with floats Thats GPH ofcourse)
new blower (double the speed of old )
ALL new chrome pieces on boat
Repaint and reseal and coat the boat
chrome dipping of windows surrounds
new steering wheel
new throttle lever
new stereo
new fuse blocks
ALL new wiring
rebuild starter
redo floor
refiberglass the stringers (while floor is off )
new floatation in the floor (also while floor is off )

WORK WORK WORK AHEAD OF ME LOL