SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: MerikaRogers on January 24, 2018, 12:19:59 PM

Title: Cam question.
Post by: MerikaRogers on January 24, 2018, 12:19:59 PM

Looking for recommendations. I've got a 454 30 over with stock parts 750 Holley and through transom headers. I Think I have a lobe going flat and wanna replace the cam and lifters before something bad happens. Just wondering what get

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

Title: Re: Cam question.
Post by: 86caribbean on January 24, 2018, 01:17:08 PM

First thing is to be sure you actually have a lobe going away, take an oil sample to see if there is any signs of metal. Then pull the spark plugs so you can perform a compression test to possibly pin point the problem cylinder, then pull off both valve covers and roll the engine over to check for excessive clearance between the rocker arms and valve stem tips. Then if you think you found the suspect lobe, install a dial indicator on a known good lobe, intake or exhaust, and take a lift reading at the rocker arm/valve and compare it to the suspect lobe. Sad news is, if you actually have a lobe/lifter that is failing; the metal contamination has already traveled throughout the entire engine's oiling system and impregnated into the cam, main & rod bearings, it’s time to completely dissemble the engine have everything properly cleaned and certain components replaced and prepare for a clean fresh assembly, that’s if someone wants to do it right, short cuts could result in another premature failure due to the residual contamination….good luck

Title: Re: Cam question.
Post by: bobjthomson on January 25, 2018, 12:02:06 PM

X2 , don’t risk it . It’s what I am in the middle of


Sent from my iPhone using SoCal Jet Boats

Title: Re: Cam question.
Post by: 96Laveycraft21Xt on January 25, 2018, 04:46:28 PM

Well, when you get the problem sorted out, i would highly recommend the Schneider Racing JB3 cam.  Just put that into my Boss's 454 (468) and pulled 503HP.  It is a marine cam designed for jetboats and performed GREAT . I also had a 750 carb  8) :thumbup: :beer:

Title: Re: Cam question.
Post by: MerikaRogers on January 25, 2018, 05:27:35 PM

Quote from: 86caribbean on January 24, 2018, 01:17:08 PM

First thing is to be sure you actually have a lobe going away, take an oil sample to see if there is any signs of metal. Then pull the spark plugs so you can perform a compression test to possibly pin point the problem cylinder, then pull off both valve covers and roll the engine over to check for excessive clearance between the rocker arms and valve stem tips. Then if you think you found the suspect lobe, install a dial indicator on a known good lobe, intake or exhaust, and take a lift reading at the rocker arm/valve and compare it to the suspect lobe. Sad news is, if you actually have a lobe/lifter that is failing; the metal contamination has already traveled throughout the entire engine's oiling system and impregnated into the cam, main & rod bearings, it’s time to completely dissemble the engine have everything properly cleaned and certain components replaced and prepare for a clean fresh assembly, that’s if someone wants to do it right, short cuts could result in another premature failure due to the residual contamination….good luck

The reason I think I have a lobe going flat is cuz it pops wide open. Total timing is around 32 and plugs look good. I should check compression again tho....  I once had a rocker arms stud break due to a collapsed lifter ( I think) but no damage was done.

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

Title: Re: Cam question.
Post by: GT Jets on January 26, 2018, 12:59:51 AM

Quote from: MerikaRogers on January 25, 2018, 05:27:35 PM

The reason I think I have a lobe going flat is cuz it pops wide open. Total timing is around 32 and plugs look good. I should check compression again tho....  I once had a rocker arms stud break due to a collapsed lifter ( I think) but no damage was done.

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

The popping is likely not a flat cam, I would be more inclined to call it ignition "cross talk" or carburetion.

What compression ratio? If it's a low compression deal, you will want to stay smallish on the cam choice, if a cam is going, your best bang for the buck will be a tear down and possibly raising the CR and going throuhg the moving parts to ensure micro metal isn't having its way with you.

A quick oil analysis will clue you in to what's wearing out in the motor.


GT

Title: Re: Cam question.
Post by: MerikaRogers on January 27, 2018, 12:53:15 PM

Quote from: GT Jets on January 26, 2018, 12:59:51 AM

The popping is likely not a flat cam, I would be more inclined to call it ignition "cross talk" or carburetion.

What compression ratio? If it's a low compression deal, you will want to stay smallish on the cam choice, if a cam is going, your best bang for the buck will be a tear down and possibly raising the CR and going throuhg the moving parts to ensure micro metal isn't having its way with you.

A quick oil analysis will clue you in to what's wearing out in the motor.


GT

What should the fuel pressure be at wot? I'm wondering if that could cause the pop

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

Title: Re: Cam question.
Post by: GT Jets on January 29, 2018, 11:57:37 AM

Quote from: MerikaRogers on January 27, 2018, 12:53:15 PM

What should the fuel pressure be at wot? I'm wondering if that could cause the pop

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

A lean pop is what I was thinking...

Fuel pressure should NEVER drop below 5# on a Holley.

GT

Title: Re: Cam question.
Post by: MerikaRogers on January 29, 2018, 12:30:50 PM

Quote from: GT Jets on January 29, 2018, 11:57:37 AM

A lean pop is what I was thinking...

Fuel pressure should NEVER drop below 5# on a Holley.

GT

Rite on I'll have to check that. Thanks gt

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

Title: Re: Cam question.
Post by: crewchief22 on January 29, 2018, 06:32:06 PM

When it does come time to replace the cam, don't jump on the bigger is always better band wagon.  Depending on cylinder head castings you could be limited to .560 range maximum lift before you start interference with the valve stem seals.  If you do pull the heads for overhaul, be sure to have the spring seats cut down so there isn't any restraints in the future.

Title: Re: Cam question.
Post by: 69kona on January 30, 2018, 05:24:52 AM

Quote from: crewchief22 on January 29, 2018, 06:32:06 PM

When it does come time to replace the cam, don't jump on the bigger is always better band wagon.  Depending on cylinder head castings you could be limited to .560 range maximum lift before you start interference with the valve stem seals.  If you do pull the heads for overhaul, be sure to have the spring seats cut down so there isn't any restraints in the future.

Crewchief 22


Sent from my iPhone using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)

Title: Re: Cam question.
Post by: jh77ie on February 04, 2018, 08:27:42 AM

I agree with GT sounds to me like a lean pop at wot had the same thing happen to me check to see if you have a loose line at the carb could be sucking air

Title: Re: Cam question.
Post by: MerikaRogers on February 07, 2018, 05:20:50 AM

Quote from: jh77ie on February 04, 2018, 08:27:42 AM

I agree with GT sounds to me like a lean pop at wot had the same thing happen to me check to see if you have a loose line at the carb could be sucking air

Haven't checked that yet.. mybe that's the prob. Took it out last weekend and had no pop. Ran good. Maybe it fixed itself hahaha

Sent from my XT1254 using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)