I`ve just discovered I had a flat lobe on one of my engines. I pulled the engine to swap the cam. My intentions were to replace the one camshaft, re-install engine and continue boating for at least another month or 2.
To speed up this process, I went ahead and bought all the parts that I`ll need. I had to order the cam, but it came in a couple days ago.
I`m working on Merc 420 with flat-tappet hyd cam.
I assumed these engines were original and still running all the OEM Merc pieces. Therefore, I ordered a replacement 420 hp spec camshaft. I was wrong.....
Upon removing the engine and pulling the camshaft, it was apparent that these engines had been into before. After removing the cam and checking the numbers, I realized that this cam was not a 420 hp spec cam, but merely an RV type, mild performance replacement.
So now I`m kinda in a dilema..........
Do I order a cam that matches the cam I pulled, so that each engine will match, even though I`m leaving horsepower on the table ?
Or do I order another 420 hp cam and yank the other engine and install the CORRECT cam in both engines ?
Or do I order a pair of hyd flat tappet cams to upgrade the performance, custom grind, etc ?
OR.....Do I pull both engines and swap the entire valvetrain to ROLLER ?
Either way, I`m probably done for the season.....

These engines never would pull past 4800-4900 rpm, so now I know why.
Having the correct cams in should help out, but I`d really like to go roller and eliminate all these flat-lobe problems --- but that`s a fairly big expense.

Here`s the specs for the Merc 420 cam :
.530 / .551 --- 228* / 236*
2800-5800 rpm

Here`s the specs for what is in now :
.529 / .525 --- 222* / 234*
2200-5200 rpm

I always wondered why these engines idled so smooth for 420`s..........

WHAT WOULD YOU DO ???

At minimum bring engine's up to 420HP specs !!!

That's what came with the boat when new and that's the minimum that should stay with the boat if it get's passed on.

Plus, all other advice from 'like Sutphen' owners give you will be more accurate for you.

BTW: I personally would never install a flat tappet again, unless forced to by a rule book, which I have to do at times. Just not worth it anymore.

If you stay flat tappet talk to a cam expert on getting better cores and better lifters than what the the companies list in catalogs. There are better components available, even if the guy on the tech phone doesn't know it.

If you wiped a lobe the engine needs minimally new bearings. This includes total teardown and cleaning of block and all parts, new oil coolers ect., aside from a new stick and lifters. Any less and you will not be happy.

BT

Being in the position that you are, I would consider bringing the engines up to date with some hydraulic roller cams/lifters. They will give you more power, and reliability with basically no "break-in" period vs flat tappet hydraulic cams/lifters which need to be "broken in" properly and are quickly becoming a thing of the past.

After discussing the budget with my financial advisor, the wife has given approval for the extra expense of swapping in roller cams. Looks like I need to contact Bob now...

Sweet on the HRC's! CUSTOM HRC's.

Bearings are too cheap, not to.

Go for the Crane Golds, too.

I am conversing now with Bob about cam selection. I have decided to refresh both engines while they`re out.

I already have the Crane Gold rockers.

I have more power than you are looking for 650hp what I am getting to ,I LET Isky cams helped me pick my cam out, and will use them for ever. I went from 595hp to 650hp with cam and head change from what we built before.

HigherPower

I too am in need of going over my 420's. See attached link.

http://www.offshoreonly.com/forums/s...d.php?t=137967

Please enlighten me on your cam selection. What did you and your 'accountant' feel would be required in $ to go to the roller setup? I too am in need of negotiating with mine. )

I got 850+ hours out of my motors so I a wondering if I really got lucky or is there a need for the upgrade?

Thanks in advance.
Trevor

It is a pretty expensive conversion. Cam, lifters and pushrods are about 1000.00 a set. Changing valvesprings is also required because hyd rollers require more spring pressure and generally have more travel. Also a cam button is required to limit fore, aft movement of the cam. It's probably good for 50 more hp than a standard 420 cam though.