TylerBurich

Yesterday i had the boat out with hopes of breaking in the new motor. Boat is a 88 formula 311 with merc 420hp 454's. Boat ran great for first hour of use, did a lot of cruising sweeping from 3k rpm all the way to 3800. On the way back to the ramp the motor started popping through the carb so i shut it down immediately to prevent any more damage. After reading some threads on here i am almost sure it is a valve train problem more specifically a cam issue. My question is.....what IS the proper procedure to break in a new cam. My new motor was not dynoed before installation, i believe the motor only had just over 1 hour of run time before popping occured. Did i do something wrong???? I hope the marina can fix this before labor day, boating season in illinois just ain't long enough!

Griff

You need to run a flat tappet cam at 2500-3000 rpms for the 20-30 mins on a new install. Run it in nuetral at the dock. Do not let it run at idle!!!!

TylerBurich

the marina ran it for about 15 min. at that rpm, i was there when they did it. who knows, maybe it's another component in the valve train that failed....we'll see. she goes in tomorrow for them to look at.

jackhammer

I chased a popping carb all the way from valve train through carb... finally replaced distributor and all ignition components for the fix.

blue thunder

Cut open the oil filter and look for magnetic flakes of death. In addition to what Griff said, it is important to run the right oil with flat tappet cams. Rottella T works well and add in STP oil treatment for extra protection. Heavy metals are not in the non diesel oils anymore, they are what helped make flat tappet cams live. Roller cams are fine with todays oil.

TylerBurich

Heard back from the marina today. Intake valve on cylinder #1 stuck open, that is causing the backfire through the carb. The head comes off tomorrow for further inspection....in the meantime...any guesses anybody?

KAAMA

iTrader: (1)

Not exactly sure what may be the cause, but it sounds like perhaps the valve guide clearances may be too tight which is usually typical of an engine builder who is used to building car type engines vs marine engines. Marine engines usually need to have the valve guides of the heads honed for greater clearance vs a car type engine.

mrhorsepower1

The proper camshaft break in procedure would be to NOT run the engine at 2000 RPM in neutral. This is the ABSOLUTE WORST thing you can ever do!!! When you are off the idle circuit of the carb, you are into the main jet. You are dumping tons of fuel into the engine which is not being effeciently burned because the engine is not under load. Let the engine warm up slow and get water temp, Take the boat out and run it normal. Ease on plane, tuck the drive in and build oil temp slow. After you have oil temp you can loosen up the trim on the drive a bit and vary the engine RPM. RPM range for the first half hour should be between 2500- 3000.

jmherbert

Thats OK for rollers but not for flat tappet, not per cam manufacturers!

http://www.cranecams.com/pdf/548e.pdf

I'd bet 99% of engines in neutral @ 2500-3000 RPM are still in the idle circuit. You barely need to crack the butterflies when there is no load on the engine. I've had brand new carbs idle that high out of the box, before the idle speed screw was adjusted.

mrhorsepower1

BS....Camshaft manufacturers recommend the 2000 RPM to protect themselves. There is plenty of oil flying of the rotating assembly at idle to lubricate the camshaft. Believe me.....50 years of experience in the biz here bro. I am just trying to shine some light on a topic which is very misinterperted. I have never lost a camshaft yet doing things our way but, I have seen others kill engines do things the cam company way.