'89 7.4L with prob. wiped cam- what grind to use?
 

I'm helping a buddy with a boat he inherited recently. It's a '89 mirage with a 7.4L/bravo 1 and through-hull exhaust. All he knows is that the engine was "bored out and had a cam installed". It does have a comp cams sticker on the valve cover.

Short version: what cam should we use (on a budget)? I'm thinking an edelbrock performer rpm or summit racing brand.

Long version: Boat lost power and only ran 40mph. Next time out it only ran 15mph with no power. Now it won't start. He had weak spark and replaced coil, dist, wires, plugs- now good spark. Bad fuel- replaced all 40 gallons of it. New edelbrock 750cfm carb. Engine has an edelbrock performer 2-0 intake- I'm going to get him a square bore to spreadbore adaptor for the engine. He had bolted the carb straight on.

Engine still cranks slow- new starter, batteries. Starter melts. Replaced. Battery cables melt. New cables.

He runs out of ideas and calls me up. I recheck all his work and we have good fuel, spark, and timing. Engine turns over very slow. I check all accessories with belts off and they turn freely. Something is holding up the engine.

Compression test reveals #2 and #3 have 30psi. Another is 90psi, the rest have 130-150.

So either the rockers are broken, came off, or more likely, wiped a few lobes off the cam. That would explain the hard to turn over since the valves are remaining shut. Also explains the burned up starter and melted battery wires.

We're going to tear it down this weekend. If the cam is shot- what should I replace it with? He's on a very limited budget- so we'll do this bottom dollar. I'm thinking a summit racing or edelbrock cam/lifters, and a felpro gasket set. He should be back in business.

I don't know how little you are wanting to spend. If you go on summit's site you can look at tons of cams and cam kits. Good luck with your build. BTW, you may want some better advice as to the cam specs before you buy. If they are too aggressive you could do some more damage when it is fired up! Just trying to give you a heads up.

Crane #134241. #134242 is kit with lifters. Priced right as well. Check to make sure his springs have the right pressure.

Either that or just use something close to staock mag cam. .510/.510, 220/220, 115 lob sep.

That's what I needed. Thanks Griff.

Cam/lifter set is $175 and fel-pro cam change gasket kit is $35.

Anyone know if the late 80's 7.4l had adjustable or fixed rockers? Will my fixed rockers from a gen VI 454 mag work on it? (I have them sitting on my workbench).

Late 80's are adjustable, why would you want to change.

are you saying the thing still cranks hard w/ the plugs out ? if so, not the cam. you will find out when you tear it down but wouldn't exactly go buying anything before i took it apart...

Good advise, don't buy anything until you tear it down.

You can buy a complete rebuild kit including pistons, rings, bearings, timing set, cam, oil pump, and gaskets for around $500...


My guess is that a couple of those cast pistons melted and that is why you have low compression. Unfortunately, been there, done that with a Gen 4 7.4L...

I've got a 120 hour stock 330HP 7.4L cam sitting in my basement free to anyone that wants it.

sounds like bad bottom end, not top end...

Fixed rockers will not work with the crane cam I posted and the stock stamped ones probably won't either. You will need a long slot stamped rocker or roller rockers.

I was just asking about the fixed rockers in-case he has some broken ones.

The engine spins over like a maniac without the plugs in it- so it's top end.

What cam will work with the stock rockers? He's not going for speed- he just wants to go boating. I only think it ran 50mph when it worked right.