92nsx

Well OSO, I have about 580 +,-Hrs. on my Gen V (1994) 502 MAG EFI. Im down on compression on 2 cylinders, and have been planning on removing the heads and having them rebuilt over this winter.

I have searched but didnt find much info on removal "tricks" or direction. I did find a old thread about using "Isky" retainers...

Any certain valves, springs, clips, retainers, ect you guys have used in your heads? Or just just have the shop build it with comp cam stuff?

Any particular things to look for in the heads and or engine block wile it is apart? BTW, I plan on doing this with the engine still in the boat.

On ressiambley, any "special" gaskets that need to be used, or standard Falpro's work just as good. Any areas that need special attention?

Thank you for the help, Rob

TooTall

Cometic MLS gaskets work great vs the felpros

92nsx

^^^ COOL! Ill get them. Thank you.

So............I'm the only person that has ever had to rebuild heads on a 502 EFI?????????????!!!!!!!!!!!!!

OSO members have no help full info

FIXX

iTrader: (2)

which cylinders? if their side by side and you kept running it then you might need a block..in other words if its 1 & 3 ot 3 & 5 or 5&7,,,2 &4 or4 & 6 or 6 & 8..if they blow between each other and you keep running it it burns a spot between the cylinders and theirs nothing you can do to fix it besides deck the block if its not to deep..

you should not listen to people that throw out names of gaskets,mls gaskets which are cometic and 1074 felpros require a vary fine finish and the deck and head surface cant have any bumps or corrosion or they wont seal..

just my o2..

and to answer the oe ? its way too far drawn out explanation to service the top end,,at the amount of hours you have,a sell you engine knowing that it needs a rebuild and find a newer motor that someone else stuck all kinds of money in or b yours needs a rebuild and will most likely cost you 5-6k to rebuild when its all said and done..

92nsx

Nope no side by side. Cyl #3 was at 100 psi, now at 25... and #4 is at 75 psi. The others are 125-135. No sings of BHG, blowen head gasket. (very common on the 7m engines.....) #3 just happened last time out. Labor day, I could smell the raw gas and knew something happened, then when back to shore.

5-6K to rebuild BBC heads!!! No way. Maybe a complete performance rebuild of the 502 would be but not on heads. Head rebuild / gaskets maybe 1K$ MAX. Local shop will rebuild the heads 5-600, and there cant be more then $400 in gaskets...

Now, when I remove the heads and there is burnt up pistons, that is a different story.

As for Cometic HG's if there the same that is used on 7M's (Toyota supra engine I have built in the past) there good HG's (3 layer MHG). And yes RA of IIRC 60 or better is needed for them to seal. BTW my straight 6 cly, 3.0L made way more power then the stock 502...

This is just my first marine engine, and figured there are some tricks to removal, and working on the 502.

92nsx

Well guys, I got the heads off.

Found blowen head gaskets!!! Blowen between 2-4, and 3-5. Both banks...

This is between 2-4,




This is between 3-5,

f_inscreenname

Wow! Never saw that before like that.
One thing is to make sure you get a Gen V head gasket. They are different that the other 454's.

cubicinches

Do yourself a favor and have the machine shop replace the exhaust seats. GM used a powdered metal seat in those cylinder heads, and if they're not loose/falling out right now, they will be eventually. I always replace the seats in those castings with an SBI/JLoy SB2000-3N seat... better material than the powederd metal, and they stay put forever when installed correctly.

I'd use a Fel Pro 1075 MLS gasket upon re-assembly.

TooTall

get your injectors cleaned also, looks like you had a very bad lean condition judging from how clean the pistons are with the low compression

kneeslider74

Not sure if you have got them done yet, but if you have not see Jim at Miller mall machine shop. He did a set of 990's for me and the Dyno guy swore that he had acid'd them. They flowed to 7500 rpm without laying down. He is a great guy. but very busy. Make sure you have Jim do the work!
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