What cam???
 

Ok, so I got a 91' mx19 as a project. 4.3l merc Engine is in pieces. With the boat I got reconditioned heads, crank, and block. Now the block is a casting number 1986, is bored .060" over. But in all the boxes I got, there is no cam or lifters. Just pushrods. So I'm trying to find out if this would have been a flat tappet or roller. I just put a GM crate 4.3 in a friends 91' Chevy truck and the original mill with over 350k miles was a roller. But it seem Merc was all over the place in using both. Anyone have a clue what I should go with? Hoping it's a roller as to avoid the flat tappet cam break in!!!!! Thanks

Re: What cam???
 

Anybody have any input?????

Re: What cam???
 

You might get somewhere on mercruiserparts.com and search a serial or model or year. The diagrams might help you out. I dont personally get into these engines to know about the valve-train.

Re: What cam???
 

I just picked up one of those Clymer repair manuals for Mercruiser engines and out drives for years 86-94 and it says Merc didn't start using the 4.3l Gen2 with the roller cam and balance shaft until model year 1993. So I guess mine will be the flat-tappet cam then.

Re: What cam???
 

What I've found says roller. What's the push rod length ?
Flat tappet use 7.8" rods whereas rollers use. 7.3".

Re: What cam???
 

Push rod length is a hair over 7.75". Which I think are flat-tappet push rods. Roller push rods are like 7.25".

Re: What cam???
 

I didn't catch the 1986 the first time around. Best I can find, 1987 is when they went roller.
I wonder why the 86 motor in a 91 boat ?
But there ain't nothing wrong with flat tappers. Just have to add zinc at every oil change unless you can find SJ rated motor oil. Last time I looked, it was up to SN on the code. I think you could use Valvoline VR1 20-50 and be golden.

Re: What cam???
 

I don't think the block is the original one. Original one must have cracked because I sandblasted the exhaust manifolds and one was cracked and the other had epoxy in a crack. I don't have the original block but the guy said all the engine parts that I got came out of the original engine from the boat. That's why I concluded it was a flat tappet because of the pushrods length. I know there's nothing wrong with a flat tappet cam, just was trying to see what my boat originally came with. Plus I hate doing flat tappet cam break ins!!!! Thanks for your input though, appreciate it...🍻

Re: What cam???
 

You going to convert to roller ? You've got to buy a cam and I'm ass-u-meing that you have no lifters. Change the dizzy gear and new push rods and you'll have a roller motor with no worries of cupping.
Just saying...

Re: What cam???
 

In addition to needing the things you mentioned, I would also need the lifter guide plates, lifter hold down spider, and I think it takes a different cam gear for the timing chain. I don't think my block has the bosses for the lifter hold down plate. I'll have to go out and check, I just picked up the block from the machine shop.

Re: What cam???
 

Dude. I'd leave it flat. I was just showing off I knew about rollers !
New lifters will come with the tie bars and you wouldn't need the spider. The spider holds the alignment of the lifters. And your right, you'd have to change dizzy gear. $60 for stock. Something know one mentions is a thorenson bearing for can walk. A cam button doesn't last long. (As I've found out!).
I've NEVER worked nor not built a marine motor but I'm doing a ton of research on them. Totally different beast from all my off road machines. I had every intention of taking one of my 640hp 6.2 LS motors I've built and putting it in. I've learned they won't live long not will my Bravo III outdrive. I'm taking my stock stuff and going to do the usual port matching, radiusing, chamfering of oil ports, and ARPs all around. Point being, stay stock ! Back pressure is your friend on marine. Love seperation is VERY VERY important.
I sure do like working on my boat cause for the first time, the entire family benefits

Re: What cam???
 

Oh I am going with the flat!!!lol just hate doing the cam break-in. I rebuilt the 350 tbi in my truck last summer and went with the flat, RV cam. An LS engine wouldn't last? Why is that? They are bulletproof in the trucks. 600+ hp in a boat would be insane!!!

Re: What cam???
 

Don't let me mislead you in thinking I have hands on experience. Just repeating everything I've researched.
I was under the impression that the Mercruiser 454 was JUST a rebadged, street engine. Not so. The spinning gear is all specially formulated parts. The piston have a very low silica ratio for possible water contact. The rods are heavier duty than anything GM ever offered. Sodium filled exhaust valves came from Mercury. Our engines are much beefier than their street versions.

Now, this is my opinion so take it as you wish;
The LS is the "smartest" engine ever built by any manufacturer. The cathedral intake runners, the windows on the main crank caps. The simple but major problem solving "steam pipe". The six bolt caps to the powder metal con rods. All smart and all stronger than anything, anyone, has ever made before.
But
The block is vulnerable without that awful ugly oil pan. The pan is actually structural and if you you replace it with a pretty gold anodized Moroso, the block WILL contort and twist, taking the main bearings with it. Slow death but it still will cause uneven wear across the bearing. To save weight, the bell housing of the 4L60 and 80 are figured into structure and it is engineered that way.
Here's a huge issue for me and not doing the LS. The programming running these beast are looking and struggling to keep the stoic...stoic. The OBD-II and the evil, CAN bus are ALWAYS struggling for that 195-205 water temp. Too cool, it leans it out. Too hot, richens it. So, the O2s can't get hot enough and the flip flopping between open loop and closed looped etc etc etc.
hands down, I believe (opinion again) the LS is the only way to go in a consistent and semi-controllable environ like the street. But when you start throwing constant water temp changes, crazy humity changes (MAP sensor) and I can see a programming nightmare.
Oneday, I'm going to look for folks who've made the swap. I'd like to see how they overcame the issues I named.
One last thing I just remembered.
All of the motors I've built over 500hp, all had to run on V-MS109. It's $750 a barrel (54gal?). That's around $13 a gallon. I could back some timing out on the cam gears but that's a lot of tq thrown away.
I believe Mercury did their homework on these motors. As bad as I want to hop it up just a little, I'll heed the warnings from those that scream "Leave it alone!"

if you take anything from what I've said, take this one thing. Get the biggest push rods you can ! I know a fella running a twin turbo 4.3 and he was constantly bending the 3/8 rods. He was running a very mild cam and low CR due to the turbos. After he bent the second set, he brought to me (us) and I measured with my adjustable and got the rockers centered on the valve stems. The third set of rods were the Comp Cam 3/8 chromos and he bent them !
Comp "comped" him and he went to the 7/16". That was 2 yrs ago. We would have gone with 1/2" but the guides were too small.

Re: What cam???
 

IF a guy were to swap an LS into a boat, I would forego the EFI and just get a 4 barrel intake made for the LS....would simplify things immensely.

Re: What cam???
 

I agree on the simplifying but those electronics are the magic of the LS. Really, any modern engine. I hated OBD systems when they first came out but I forced myself to learn the 5 major sensors, counting the IAC as a sensor, and not including any speed density,and haven't looked back since.
BTW. Do you have any clue how you could mount an O2 sensor in the exhaust ? I could bung it up so it stayed dry but you'd think the steam would dilute the exhaust mixture.
I'm going to put a bone stock 1997ish Mercury MPI. I have access to a complete system. I wonder if it's speed density...
Was going to do a complete FAST 2.0 set up but everyone has talked me out of it. Seems the Bravo III is running at the ragged edge with 400hp.
My hole shots are non existent. And my top end, right now, is in the 35mph range.