Early SBC dipstick issues with Alpha exhaust

[benny92lx]

Hey guys, i recently picked up a command with the Alpha 1 drive. Stock mercruiser exhaust that has a cracked block. I ended up purchasing an early based 383 with aluminum heads. long story short, i was swapping pans and realized that the original motor had a later 350mag engine with the one piece rear main. not know chevy's to well, i didnt think anything of it. But then i quickly realized that the 350 had a starboard dipstick that was intricatly routed dipstick that brought it to the front of the engine. I however, cannot use that dipstick on the 383 being that it is a port side dipstick that enter at the headgasket level. normally it wouldnt be an issue, but i plan on using the stock mercruiser exhaust which conflicts with the new dipstick location.. has anyone else had issues with this? and how did you resolve the issue? im hoping i dont have to buy a new oil pan with a pan mounted dipstick. im open to suggestions. thanks!

 

[Scott Danforth]

a couple of things. while not impossible, it can be done.

first, on to the pre 1981 383 that you bought. with aluminum heads, you should run a heat exchanger. also, is this a motor built for marine use? what is it?

unless the motor was built up as a tow truck motor, it most likely was built as a high-compression motor for someones camaro. so the motor would need to be pulled apart 9:1 or lower compression and a marine cam would need to be installed. then the head gaskets would need to be marine and the core plugs brass.

now on to the flywheel. you will need to buy a new flywheel as the one that was on your original boat motor wont bolt to the 1-piece crank. you may also need a new coupler

as for the dipstick, you have to replace the dipstick tube in the 383 with a marine one (goes to the bottom of the pan) or get a marine oil pan with a dipstick tube that goes to the bottom of the pan. so either a really early mercruiser tube and stick or a new oil pan.

If the motor was not built for marine, I would simply sell the 383 that you bought and build one for marine use with new block, heads, crank, cam etc. for about $3k

 

[benny92lx]

Hi, it was built for someones camaro. but the compression is sitting at 8.7-1 with the MLS Marine gasket. The cam is subtle enough to work with my setup and not promote reversion. The heads are getting worked over with the valve guides getting a marine focus. Im also having inconnel exhaust valves put in while its there. The whole motor is getting reworked, new rings with looser gaps, new bearings, all now bronze plugs. New flywheel was bought bought and should work with the mercruiser drive hub which only has 3 bolts that bolt to the flywheel. I have all of that on lock down. It was just a kick in the pants when i over looked one small detail.

as for the dipsticks, you would happen to have a link for marine use dipstick. i cant find one anywhere. thanks for the response!

 

[Scott Danforth]

list your cam specifics. lobe center and duration at a minimum. if your cam 112-114 degree lobe center and under 268 degree of duration with a moderate lift, then it may be subtle enough. however every automotive cam out there is wrong for marine use as most are 108 lobe center. which is why when building a marine motor, think RV or dump truck (Which is why most RV cams are Marine cams) base timing also has a lot to do with reversion. I found that out the hard way.

you still need a heat exchanger with aluminum heads for both corrosion reasons and combustion temperature reasons

look at the parts break down for pre 1981 mercruisers.

 

[alldodge]

swapping pans and realized that the original motor had a later 350mag engine with the one piece rear main

Without knowing the exact year my guess would be items 18 and 19

http://www.mercruiserparts.com/bam/subassembly/31745/2691/210

As years progress the tube changes a few times

http://www.mercruiserparts.com/bam/subassembly/31751/12840/140

 

[benny92lx]

Its a comp cams 12-420-8 which is 215/215 lift, 270/270 duration, 110 lobe separation. its a little tight on the separation but should be mild enough on the lift and duration.

Thanks for the link all dodge! but those are for the dipstic on the opposite side of the engine. I need them on the driver side. I guess the real question is if the dipstick tube would fit between the exhaust manifold and the head. Looking at the old mercruiser 260's, it looks like thats what they did. but im not sure if the exhaust manifold is pushed out a little further to warrant more clearance between the manifold and head.

 

[benny92lx]

Also, thanks for the reply Scott. With as little as this boat will see the water (3-5 hours from havasu) and zero time on salt water, im really hoping to not have any severe corrosion on the heads, but i will look more heavily into an exchanger during the winter.

 

[Scott Danforth]

Its a comp cams 12-420-8 which is 215/215 lift, 270/270 duration, 110 lobe separation. its a little tight on the separation but should be mild enough on the lift and duration.

Thanks for the link all dodge! but those are for the dipstic on the opposite side of the engine. I need them on the driver side. I guess the real question is if the dipstick tube would fit between the exhaust manifold and the head. Looking at the old mercruiser 260's, it looks like thats what they did. but im not sure if the exhaust manifold is pushed out a little further to warrant more clearance between the manifold and head.

you WILL have issues with that cam because of the lobe separation and that you are over 268 degrees of duration if you are running traditional wet exhaust. suggest you go fully jacketed until after you exit the transom or change cam.

this is the marine cam where you start to run dry exhaust. this is a jet boat cam http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=100&sb=2

this is the biggest cam you run on a flat tappet motor with wet exhaust running a thru-leg exhaust. http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=99&sb=2

 

[benny92lx]

Thanks for the insight. it looks like im going to abandon the 383 project. Just too many loose ends, and the fact that the engine builder i had lined up is no where to be found. I found long blocks on summit for pretty resonable. ATK marine, heard of them?