502 rebuild questions ,,,, AGAIN !!!!!
 

Not to beat a dead horse, but I have the motor apart and have a few questions,,,,, the heads I have down,, bronze guides and teflon seals seems to be the answer there.

It is a 95 MPI NON roller motor,,, is it worth switching over to roller cam/lifters? what cam can I use,,, roller and flat tappet specs. will the stock ECM support roller cam gains?

What rings are everyone using?

Also, I remeber a thread about grooving the heads for a special type head gasket,,, is it a good choice for a non blower motor?

Also,, has anyone used "coated " bearings,,, my motor guy recomended them. They had a grey coating on them,

CANT WAIT FOR SUMMER !!!!!!!!!!!!

Build a 540 motor out of it. I ran JE pistons and rings.

obnoxus, if you can, make it a 540. The roller cam will outrun a flat tapped to death, but if you do ANYTHING to help performance much, you better have someone modify the computer!
I would talk to Jim at Arizona Speed and Marine.
I have tried many different rings, na and forced induction.
I do not like zero gap rings on the second ring. Zero gap top rings are the ticket, but you must follow dorections to the letter-which stone, load, number of strokes, etc. If you don't, you may have trouble. We use Speed Pro file fit most of the time. I have used several brands and had some success with them as long as you get the performance set recommended by the manufacturere. If you use JE pistons, they will sell you rings with them at a very good price and are excellent rings.
I had the thread about head gaskets and I would NOT use the receiver groove head gaskets on anything but all out engines. Fel Pro and Cometic are my choices, but there are many other good ones available.
I like to use coated bearings. Calico Coatings in NC can fix you up at a good price and recommend the proper coating for your application. Their number is1-888-236-6079. There are lots of others who can supply quality parts also. Any more help I can be, just post or pm:D :D :D

Remember,,,,, MPI !!!!!! Stock rebuild,,,, the only thing I am considering is roller valve train to bring it to gen6 specs,,, wondering if its worth it !!!!!

I have 2 people interested in the boat,,, I just want to give them the best and most reliable engine I can.

In the can thread there was 2 specs that were posted as stock for the MPI motor,,, a 483, and a 511,,, which is it?

If I was keeping it the 540 route sounds sweet !!!!!!!!

a roller cam can pick you up to as much as 50hp with the same grind as a flat by parasitic friction reduction and increased valve speed. that means the fuel curve will need to be remapped slightly.
a roller cam is also not a straight swap. different lifter companies have diffent height lifters, you may need custom pushrods after checking the valvetrain geometry. the cost of a roller cam without the lifters is more than the cost of a flat cam with lifters in most cases.
i am of the opinion, if your selling the boat, keep it stock, save your money. with the money you saved you can start building those 540's. better yet, a 4.25" crank and a 4.50" stroke crank cost the same so build a 572 instead.:D

Thats part of the reason I have to question Mercruisers ratings,,,, The motor is a 95 MPI rated at 415 prop hp,,, but a 97 502 MPI roller valvertrain is also 415 prop HP,,, WHAT GIVES !!!!???:confused: :confused: :confused:

Yep,, according to my service manual both are rated at 415 prop hp,,, HOW CAN THAT BE !!!!????

\


ANYONE !!!???

roller cam
 

I run a 502 EFI (manu - 1995 - no manual fuel pump on block - no port for one). Had #8 exhaust fail in the third year. After trusting a "local shop", the second year following "I" pulled the motor and did the work myself --- up graded to a crane roller cam and roller lifters, push rods and springs and 10 deg. titanium keepers-- all crane stuff. Per Merc's specs, I dropped a little duration and picked up some lift. What everybody tells you the valve speed in faster with the "roller" so even with the same specs the "roller" cam gives you a fatter opening period.

Unfortunately, I didn't see an increase in speed and had some hesitation with heavy throttle from idle. Booze out of LA., did some reprograming for me, and only then did I see an increase in speed. (Very happy with Booz - did what I asked, and good follow up customer service)

Yes, it will work. Is it worth it???? I'm not unhappy with the move, and am stepping up to CMI exhaust this year and am hoping for more speed.

Crane Cam's tech line will help you a lot, but different technicians will give you DRAMATICALLY different advice.

If I had it to do over again, I would have taken more duration and more lift. ( Maybe next year...... LOL.)

MAV

MAV! I need to talk to BOOZE out of LA, please. Also, the Crane 741 works miracles in a 502!! Oh yea, you will need exhaust.

Obnoxus
 

They didn't pick up any horsepower by switching to the roller camshaft. The duration figures are the same. They picked up a smoother idle, better fuel economy and extended oil change intervals. The same reason why all of the automotive manufacturers have switched to roller cams.
Dennis Moore

THANKS FOR RESPONDING DENNIS !!!!!!

Im glad to here that,,, I was perfectly happy with it, but everyone says about this MAGICAL HP in a roller setup,,,,,

You said once before,,,,,but I cant find it,,,, without remapping my ecu can you give me camspecs,,, my builder was asking so he can order a camshaft.

AND,,, is JUST a bigger cam and remapping going to net any gains,,,recomondations? I am suddenly willing to do it,, how about gasket matching heads?

What are you opinions on timing ?
FYI,,, ECU will be done on a dyno.

THANKS AGAIN !!!!

Ask Comp Cams
 

The roller camshaft designed by GM has about 224/224 degrees of duration. The opening and closing ramps are slow, not because GM doesn't know much about camshafts, but because they have to worry about warranty claims on thousands of engines. The faster you open and close the valves, the more often you need valve jobs and more often you need to change the oil. GM doesn't like paying for warranties so they are conservative with the camshafts. Buying an aftermarket camshaft with aproximately the same duration but with quicker opening and closing cam lobes will increase horsepower and torque but generally not require reprograming the ECM. Buy a cam that has a slightly closer lobe separation angle. About 114 degrees would be fine. If you stay with lobe lift below .550 you will not have to change the valvesprings or go to an adjustable rocker arm. An aftermarket roller camshaft will be the best choice, call Comp Cams and ask them. This will be a lot of work for 20 to 25 horsepower though.
Good Luck
Sincerely
Dennis Moore

STOCK IT IS !!!!!!!!!!! Did we ever agree on what the specs were on the stock flat tappet cam !!!!!!????

Again,, thanks for the help

Crane 741
 

Blown 1500

What are the specs on the Crane 741???

MAV

stock specs / per merc publication
 

here's the #s from the Merc service manual -- keep in mind -- some people will tell you that you can't trust "published specs" ( then everybody would have the magic!!

int/ ext @ .050 lift on both intake and exhaust
224/224 .510 flat tappet motor ( merc 502)

MAV

crane #139741

.632" intake
.632" exhaust

[email protected]" intake
[email protected]" exhaust

112 LC ground with a built in +5 advance.
14 degree overlap @.050"

741
 

Thanks for the spec.s

That's a TON of lift!??!??!?!?!? How much head and valve work needs to be done to support that cam AND how much compression is needed to make it work???

Also, with this kind of lift -- how many hours between "tear downs" - for a look for broken inner valve springs?????

MAV

Figure springs every 150.
That's a dollar an hour. Cheap.

Re: stock specs / per merc publication
 

OK,, now Im loosing that warm fuzzy feeling !!!! Anymore input on the stock cam subject?

I like the idea of the slower ramp speeds as Dennis Moore has mentioned. Slower ramp speeds equates into a longer living engine/valve train. It's just much easier on parts. I have the Crower hyd rollers, but I once had Ultradyne cams which usually have VERY aggressive ramps speeds. Both the Ultradyne and Crower have the same duration @ .050" numbers 236*/244*. However, the advertised duration numbers are different between these two cams though.

Ultradyne
(advertised duration) 288*/296*

Crower
(advertised duration) 300*/307*

The Crane 139741 hyd roller is very close 236*/242* as Mcollinstn has posted, but I don't know what the advertised numbers are on the Crane---I'm not real sure on this, but I heard they're not too aggressive.

All in all, I would rather sacrifice some HP and Torque for a little more reliability and I can see why GM designs their cams profiles this way---not a bad idea in my opinion.