1998 5.0 2bbl alpha bad cylinder

[revkev6]

hey guys, I picked up a complete 1998 5.0 alpha gen II driveline to use in a 1966 formula jr project I have. motor was described as in running condition but had one cylinder that was low on compression it's a salt/brackish raw water cooled motor with 800hrs on it. I ran a compression check and found that in fact one cylinder was about 60-80 psi lower than the rest which were in the 160psi range. I put oil in the bad cylinder to see if it was bad rings/cylinders and the compression didn't change. so at this point I'm thinking it's either valve or gasket and the previous owner didn't mention water in the motor (he had it pulled at the end of the season because he said it backfired a couple times while on the water)... the motor is extremely clean as is everything that came with it. (outdrive, gimbol, trim pump, steering etc.)

so I'm heavily leaning towards valve... but I haven't opened the motor up yet. given that it is a raw water cooled saltwater motor with quite a few hours on it I'm wondering if it is worth doing the heads since the compression is pretty good across the board. basically my thoughts are, if I pull the heads and find one tuliped valve that I can replace and lap the rest back in I will run it... but if it needs the heads completely rebuilt I am better off buying a reman. 5.7 to swap in it's place considering the rebuild of the heads will be almost half what a long block would cost...

thoughts??
btw, I've got $800 into this entire setup so i think I've done good with it even if the motor is just a core...

 

[harleyman1975]

I think a simple valve job to the bad head would be 200-300?

 

[revkev6]

well, whatever I do to one head, I will do to the other as I can't see them being far apart. I would hate to get the motor in the boat with one fresh head only to have to pull the other halfway through the season. there lies my quandary.... a rebuilt marine 5.7 with 4 year warranty is less than $2k to my door... bolt on accessories and go... drop 5-600 on heads and still have a tired 5.0 shortblock... is that throwing good money after bad?? how many hours can you expect out of a saltwater 5.0??

my formula is 17' so the 220hp 5.0 is going to get me at close to 60mph anyway... I don't NEED the extra power per say. this is a low budget project that I'm trying to do with my father... haven't done one in a long time.

 

[Rick Stephens]

I would fear that a valve job would lead soon to a ring job.

 

[revkev6]

I would fear that a valve job would lead soon to a ring job.

how so?? especially given that the compression numbers are perfect at the moment. good heads won't magically make your rings go bad??

 

[Bondo]

r (he had it pulled at the end of the season because he said it backfired a couple times while on the water)...

Ayuh,.... That tells Me,.... There's crap, 'n crud in the fuel system, which caused it to run lean, which caused detonation to set in, fryin' atleast a valve, 'n possibly that piston,...
If ya salvage the carb or fuel pump, rebuild 'em, before runnin' 'em,...

If I were you, I'd just go buy a 350, 'n be Happy,.....

305s are either the same money, or more expensive than a 350,....

 

[Rick Stephens]

how so?? especially given that the compression numbers are perfect at the moment. good heads won't magically make your rings go bad??

Seen way too many times: old rings, new valve job, next thing you know is lots of blow by.

 

[Maclin]

Pretty simple to do a leakdown test on that cylinder. That will tell if it has compromised piston or rings, or if it is all in the head.

 

[revkev6]

Ayuh,.... That tells Me,.... There's crap, 'n crud in the fuel system, which caused it to run lean, which caused detonation to set in, fryin' atleast a valve, 'n possibly that piston,...
If ya salvage the carb or fuel pump, rebuild 'em, before runnin' 'em,...

If I were you, I'd just go buy a 350, 'n be Happy,.....

305s are either the same money, or more expensive than a 350,....

if I get a 350 I also have to invest in a new intake and carb... not a huge deal.. rather make it run cheap with what I have first. rebuilt motor is option 2 and it would be a 350 if I went that way.

Seen way too many times: old rings, new valve job, next thing you know is lots of blow by.

maybe if the rings are already going... but this motor seems to have good ring seal. you don't get 150-160 psi with bad rings.

Pretty simple to do a leakdown test on that cylinder. That will tell if it has compromised piston or rings, or if it is all in the head.

I did both compression and leakdown to determine the location of the leak in the bad cylinder.. definitely coming from the exhaust valve. just have to determine the severity of it. if its just replacing a valve and cleaning the rest up and hitting them with some lapping compound I'm golden.

 

[Rick Stephens]

I did both compression and leakdown to determine the location of the leak in the bad cylinder.. definitely coming from the exhaust valve. just have to determine the severity of it. if its just replacing a valve and cleaning the rest up and hitting them with some lapping compound I'm golden.

I'd go for that. I got the impression the motor was tired, maybe wrongly so.

 

[Scott Danforth]

if I get a 350 I also have to invest in a new intake and carb... not a huge deal.. rather make it run cheap with what I have first. rebuilt motor is option 2 and it would be a 350 if I went that way.

why would you think that?

you would need new gaskets and worst case, you would need to calibrate the carb a bit different. but it would be the same manifold and same carb

 

[revkev6]

why would you think that?

you would need new gaskets and worst case, you would need to calibrate the carb a bit different. but it would be the same manifold and same carb

Although technically correct I wouldn't put a 2 barrel carb on a 350...at that point the motor would get a little attention and it would be a hot boat.

 

[Scott Danforth]

your dollar, your boat. 350's come from the factory all the time with 2-barrels.

 

[revkev6]

It's the reason I'm really hoping this motor is a quick fix. If I can run it as is with a little work that is perfect and it's a 55-60mph boat with stock 305. If I drop in a 350 I start to build for speed and so my budget goes up! The drawbacks to having racing and hot rodding in your blood!

 

[NHGuy]

Formula Jr. You should be happy to be fixing that up. Love them. And you are right, a 305 will push it along just fine. BTW you can build up a 305 too. Resist!