Roller Tip Rocker Arms

[Gogonova]

I have a Mercruiser 898 (GM305CID) in my 1982 Crusiers Beachcomber boat. I also have a number of parts left over from a failed hot rod product. I understand the major differences between automotive and marine engines but has any one traied roller top rocker arms? Id also like to change the carb from the two barrel to a four barrel set up. I both a stock GM cast iron intake manfold and an Weiand low rise aluminum intake manifold. I was thinking of using a holley Quadrjet replacement Carb or a rebuilt Quadrajet. The boat will used only in fresh water. Anyone have any thought, ideas or receommendations.

I have a balanced & blueprinted two bolt main 350 CID with hyperkenetic aluminum pistons, Wold Product 76cc cylinder Heads, High Volume Oil Pump, double roller timing chain. With a change of camshaft and freeze plugs to brass, could I use this engine to replace the 305?

I have new in the box Holley 570cfm street avenger carb, a New in the box Holley Quadrajet Economize 4bbl carb, a Accel Blueprinted single point distributor for Small block chevy, with pertronix electronic conversion kit and Ignitor Coil. Anyone interested? Make an offer! I am not looking to make killing, maybe 1/2 of the new price. Cheers

 

[picklenjim]

Re: Roller Tip Rocker Arms

Roller rocker arms work great in a marine motor!They free up a little horsepower and reduce wear on your valve guides.Mercury has them on several models.That Weiand dual plane would work good also.The last time I remember though Holley didn't make Quadrajet carbs.That 350 swap I would think would work fine also.You may have to change a few things here and there but where theres a will theres a way.I'd do it.

 

[straubtech]

Re: Roller Tip Rocker Arms

Roller rocker arms with a trunion that has needle bearings and a roller tip are good pieces. Rocker arms that have a roller tip but still use the same ball and nut fulcrum are worthless. The majority of frictional loss in the rocker arm is because of the friction of the ball design fulcrum, not the pad that contacts the valve.

 

[WizeOne]

Re: Roller Tip Rocker Arms

Roller rocker arms with a trunion that has needle bearings and a roller tip are good pieces. Rocker arms that have a roller tip but still use the same ball and nut fulcrum are worthless. The majority of frictional loss in the rocker arm is because of the friction of the ball design fulcrum, not the pad that contacts the valve.

I second the motion on this.

Also, you do not want to just slap a set of roller rockers on your engine and walk away. You need to check the witness marks on the top of the valve stem to make sure the tips are riding in the right place. If they are not you can prematurely wear out your valve guides.

Here is an article on that.

http://www.carcraft.com/techarticles/116_0401_setting_pushrod_length/index.html

 

[CharlieB]

Re: Roller Tip Rocker Arms

Id also like to change the carb from the two barrel to a four barrel set up. I both a stock GM cast iron intake manfold and an Weiand low rise aluminum intake manifold. I was thinking of using a holley Quadrjet replacement Carb or a rebuilt Quadrajet............
I have a .......... bolt main 350 CID ................. With a change of camshaft and freeze plugs to brass, could I use this engine to replace the 305?

I have .......... Holley 570cfm street avenger carb, a New in the box Holley Quadrajet Economize 4bbl carb................

Mercury did use 4 barrel intakes and carbs on many models with HP increases over two barrel models.

The conversion is pretty straightforward, HOWEVER, your selection of carb is critical in that The correct marine carb SHOULD BE USED. Automotive carbs may be MARINIZED and jetted to ensure the safety of your boat, crew and everyone else nearby at the dock, vacuum ports are not necessary and should be permanently plugged, rubber caps age and fail, possibly causing a lean condition, ruining a set of pistons.

A fuel pump vent port should be installed near the top of the carb throat. DO NOT attempt to use any existing vacuum port for the fuel pump vent, the vacuum will simply STOP the fuel pump from making a stroke, the engine will immediately run out of fuel and die. (Don't ask me when I made this mistake)

Marine carbs fuel flow characteristics are substantially greater than their automotive cousins. Larger needle/seats MUST BE installed to ensure that a high speed lean-out does not melt another set of pistons.

Power valve opening vacuum ratings are different.

Main Jet sizes are different.

A marine carb cannot be allowed to leak fuel to the surrounding area, unlike the automotive carb, the marine carb vents MUST vent to the throat such that ANY overflow falls into the throat to eliminate the possibility of fuel/fumes released into the engine bay creating the risk of an explosive atmosphere.

Finally, Holley DID make a Spread-Bore series as a replacement for the Quadrajet, I still have one on my big block El Camino for 35 years and know a Gentleman that has FOUR of the same double pumpers on a shelf in his garage. And he is VERY proud of them, as I. I would NEVER consider attempting to install one on a boat.

Order the correct marine carb, it's a LOT cheaper AND safer.

Oh, keep the cam LSA at 112 or greater.
On the water, more duration requires more separation, period.

 

[J JACKSON]

Re: Roller Tip Rocker Arms

Roller rocker arms with a trunion that has needle bearings and a roller tip are good pieces. Rocker arms that have a roller tip but still use the same ball and nut fulcrum are worthless. The majority of frictional loss in the rocker arm is because of the friction of the ball design fulcrum, not the pad that contacts the valve.

wrong, true roller rocker are great in a race car but on a engine that you aren't going to check them often they are worthless they wear out fast i have changed many sets on street cars the most they get out of them is 20,000- 30.000 miles roller tips however will work fine.

 

[rodbolt]

Re: Roller Tip Rocker Arms

gotta agree with J on this.
its also why GM on the 325,330HP marinized engines use the ball and fulcrum setup with roller tips.
the point is when the rocker arm travels from closed to open and back to closed the tip actually travels in an arc not stright up and down.
this tends to wipe acrossed the valve stem actually pulling and pushing the tip of the stem.
a roller tip rocker greatly reduces the side loading of the valve stem and aides in stem life and oil leaking past the stem into the cyl.

 

[Gogonova]

Re: Roller Tip Rocker Arms

Many thanks for everyone's comments. I am finding that like cars, opinions vary on what works and doesn't work on marine engines. I've never been a big fan of Rochester Q-Jets but Holley does make marine Q-Jet replacement spreadbore carb. A rebuilt model is about $250. I am also discovering that anything for a marine engine costs approximately twice as much for a similar item on a auto engine. I understand the need for modifications to reduce the chance of explosion or fire but $600 list for a two barrel carb? Who are they kidding?

 

[Tail_Gunner]

Re: Roller Tip Rocker Arms

gotta agree with J on this.
its also why GM on the 325,330HP marinized engines use the ball and fulcrum setup with roller tips.
the point is when the rocker arm travels from closed to open and back to closed the tip actually travels in an arc not stright up and down.
this tends to wipe acrossed the valve stem actually pulling and pushing the tip of the stem.
a roller tip rocker greatly reduces the side loading of the valve stem and aides in stem life and oil leaking past the stem into the cyl.

Intresting post 3 hours ago i opened a 4.3 to see those flulcrum rockers with some type of alum cross bracket..(girdle). I really thought i had a L-98 series head or something..

Those are the type of things you see on a heavy deisel...it's amazing to see on a small 4.3....but i guess someone envisioned seeing a person running up and down the water @ wot all day.

 

[Bondo]

Re: Roller Tip Rocker Arms

I've never been a big fan of Rochester Q-Jets but Holley does make marine Q-Jet replacement spreadbore carb. A rebuilt model is about $250.

Ayuh,...

Merc went to the Weber after the Rottenchesters...
The Edlebrock Performer is a Carbon Copy with interchangable parts...

That alone saves the Headache for forming bracketry to make a Holley work...
And,..
The Edlebrocks are about the Same Money as the Holley you mention,.... Brand New....

 

[wca_tim]

Re: Roller Tip Rocker Arms

sounds workable. i would go with en edelbrockmarine carb for about 300 new.

You'll definately need to change the oil pump - standard volume only in marine engine.

which pistons did you use? as in what is your static compression ratio? Those heads will work great by the way.

What ratio are the roller rockers? and if higher than 1.5, did you have the push rod holes elongated in the heads?

sounds like would work out pretty well

 

[s1120]

Re: Roller Tip Rocker Arms

I use Roller tip rockers on every engine I rebuild. I like them. I run the Comp Cams Mangam roller tip rockers. True they dont cut as much friction as a full roller, but also they fit like OE [a lot of times you need to mod the valve cover to fit the full rollers, depending on the brand] and also they are a very high quilty replacement. Frankly I am not a huge fan of the OE stampped rocker that the GM engines use.

 

[mudweiser]

Re: Roller Tip Rocker Arms

Go to edelbrock, they have remanufactured Edelbrock 4bbl carbs. I just bought a 1409 "marine" carb and the reman number for that carb is 9909. It's only like $259.00. Check it out: http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL%2D9909&N=700+115&autoview=sku