[Bigred89]

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

[Bigred89]

Anybody have any input?????

[Motoxxx43]

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.

[Bigred89]

Originally Posted by Motoxxx43

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.

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.

[Brian Belcher]

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

[Bigred89]

Originally Posted by Brian Belcher

What I've found says roller. What's the push rod length ?

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

[Brian Belcher]

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.

[Bigred89]

Originally Posted by Brian Belcher

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.

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...🍻

[Brian Belcher]

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...

[Bigred89]

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.