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Old 11-04-2018, 10:17 AM
rossi_the_heeler rossi_the_heeler is offline
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94 Prostar 205 TBI -New Motor Time???? (Long Post Alert!)

While winterizing a month ago, I decided to get a baseline on compression numbers.
1,2,4,6,7,8 are all 140 +- 5 psi. 3 and 5 were 35 and 15 respectively. The plugs were wet and smelled like gas. I pressurized 3 and it blew out 5's spark plug hole. So certainly head gasket time. Between cylinder 3 & 5 there was 3/4" of gasket gone.

SO I tore down the top of the motor, got the heads machined and checked for cracks (the odd-side bank had a crack), bought a new one and had the speed shop do a valve job on both and clean 'em up. Put the whole thing back together and got it set timing back to 10 degrees btdc. It idles fine, rev's nicely (on the hose anyway) BUT cylinder 5 is still low on compression. All the other cylinders are good. (Number 3 came up to 145 psi now too.) Number 5 is 70 psi. I put some Marvel Mystery Oil in it for a couple days and just cleaned it out. Compression came up to 75 psi.

I stared at cylinder 5 for about 3 hours while I was cleaning up the gasketing surface of the block, and the walls didn't look scratched AT ALL. (could it be a siezed ring?)

So, I'm wondering what I should do. I feel like my options are as follows:
1. Do nothing with it (It runs, and will pull me out of the water just fine!).
2. Take it out, bring it to the speed shop and have them work on it.
2a. What are the options there? (go .030 over?)--Will this affect the TBI fuel injection/mapping? Sleeve one cylinder? Rebuild the whole dang thing?
2b. Does the cost of all this outweigh buying a used lower (block) and putting my brand spankin' fresh heads on it?
3. Should I try and do this myself this winter???? --I would have to buy an engine stand, but I am pretty mechanically inclined.

This boat is new to me about a year ago. I haven't had any overheat/temperature issues during the year, but it had to have had an overheat in it's life because cast iron heads aren't just going to crack for no reason...

I'm really just looking for a solid running boat for the next 20 years. LOLLOLLLLL(Aren't we ALL?)
Sorry for the book guys. I'm trying to educate myself, to make the right decision and keep my marriage intact...
-Aaron
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  #2  
Old 11-04-2018, 11:50 AM
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mikeg205 mikeg205 is offline
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How many hours on motor?

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  #3  
Old 11-04-2018, 12:19 PM
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JimN JimN is offline
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Quote:
Originally Posted by rossi_the_heeler View Post
While winterizing a month ago, I decided to get a baseline on compression numbers.
1,2,4,6,7,8 are all 140 +- 5 psi. 3 and 5 were 35 and 15 respectively. The plugs were wet and smelled like gas. I pressurized 3 and it blew out 5's spark plug hole. So certainly head gasket time. Between cylinder 3 & 5 there was 3/4" of gasket gone.

SO I tore down the top of the motor, got the heads machined and checked for cracks (the odd-side bank had a crack), bought a new one and had the speed shop do a valve job on both and clean 'em up. Put the whole thing back together and got it set timing back to 10 degrees btdc. It idles fine, rev's nicely (on the hose anyway) BUT cylinder 5 is still low on compression. All the other cylinders are good. (Number 3 came up to 145 psi now too.) Number 5 is 70 psi. I put some Marvel Mystery Oil in it for a couple days and just cleaned it out. Compression came up to 75 psi.

I stared at cylinder 5 for about 3 hours while I was cleaning up the gasketing surface of the block, and the walls didn't look scratched AT ALL. (could it be a siezed ring?)

So, I'm wondering what I should do. I feel like my options are as follows:
1. Do nothing with it (It runs, and will pull me out of the water just fine!).
2. Take it out, bring it to the speed shop and have them work on it.
2a. What are the options there? (go .030 over?)--Will this affect the TBI fuel injection/mapping? Sleeve one cylinder? Rebuild the whole dang thing?
2b. Does the cost of all this outweigh buying a used lower (block) and putting my brand spankin' fresh heads on it?
3. Should I try and do this myself this winter???? --I would have to buy an engine stand, but I am pretty mechanically inclined.

This boat is new to me about a year ago. I haven't had any overheat/temperature issues during the year, but it had to have had an overheat in it's life because cast iron heads aren't just going to crack for no reason...

I'm really just looking for a solid running boat for the next 20 years. LOLLOLLLLL(Aren't we ALL?)
Sorry for the book guys. I'm trying to educate myself, to make the right decision and keep my marriage intact...
-Aaron

I saw many boats with badly overheated engines and they ran fine, for years after. It's possible that yours was overheated and restarted while it was too hot and the thermal shock may have caused the crack.

Personally, I look at the fact that the Chevy cast iron small block has been used since 1953/4 as a good thing. They're plentiful, relatively inexpensive and easy to work on. They also tend to be just about bulletproof.

I would do a cylinder leakdown test- if the valves and gasket are good, it leaves the rings and not much else to cause the compression loss, assuming the oil isn't being polluted by combustion gases.

Did you re-use the head bolts?

Did you check the block for flatness, or only the heads?

If you're up for disassembly, they can check the block for cracks and if needed, freshen that up by boring/honing and if needed, sleeving.

A short block isn't terribly expensive and if you ask the speed shop, they can advise you on the next steps.
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Old 11-04-2018, 01:32 PM
rossi_the_heeler rossi_the_heeler is offline
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Quote:
Originally Posted by JimN View Post
I saw many boats with badly overheated engines and they ran fine, for years after. It's possible that yours was overheated and restarted while it was too hot and the thermal shock may have caused the crack.

Personally, I look at the fact that the Chevy cast iron small block has been used since 1953/4 as a good thing. They're plentiful, relatively inexpensive and easy to work on. They also tend to be just about bulletproof.

I would do a cylinder leakdown test- if the valves and gasket are good, it leaves the rings and not much else to cause the compression loss, assuming the oil isn't being polluted by combustion gases.

Did you re-use the head bolts?

Did you check the block for flatness, or only the heads?

If you're up for disassembly, they can check the block for cracks and if needed, freshen that up by boring/honing and if needed, sleeving.

A short block isn't terribly expensive and if you ask the speed shop, they can advise you on the next steps.


Thanks Jim,
I did re-use the head bolts. The block had a high spot in between 3&5 cylinders, right where the head was high too.
I was able to file that down flat.
If they bore it out will I need to re-map the mefi, or is the difference too minimal to cause a change in fuel mapping?


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Old 11-04-2018, 02:28 PM
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JimN JimN is offline
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Quote:
Originally Posted by rossi_the_heeler View Post
Thanks Jim,
I did re-use the head bolts. The block had a high spot in between 3&5 cylinders, right where the head was high too.
I was able to file that down flat.
If they bore it out will I need to re-map the mefi, or is the difference too minimal to cause a change in fuel mapping?


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I donít think it would cause a problem unless you do something drastic- not sure 30 over constitues Ďdrasticí but making it breathe better wouldnís be a bad idea. You could contact Indmar about that.
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Old 11-04-2018, 02:35 PM
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Double D Double D is offline
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Maybe the valves in that cylinder giving you the low compression number? My first new motor in my old 205 had the wrong plugs that overheated the valves and screwed my compression. At least thatís what I was told.
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  #7  
Old 11-04-2018, 03:05 PM
rossi_the_heeler rossi_the_heeler is offline
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Originally Posted by mikeg205 View Post
How many hours on motor?

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1100 hours. I got it with 1000.
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  #8  
Old 11-04-2018, 03:08 PM
rossi_the_heeler rossi_the_heeler is offline
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Quote:
Originally Posted by Double D View Post
Maybe the valves in that cylinder giving you the low compression number? My first new motor in my old 205 had the wrong plugs that overheated the valves and screwed my compression. At least thatís what I was told.
Thatís what I was hoping Double D, unfortunately I had them do a valve seat job on it when the heads were in the shop. I will check with the guys in the speed shop though!
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  #9  
Old 11-04-2018, 03:11 PM
rossi_the_heeler rossi_the_heeler is offline
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Boat: 1994 Prostar 205
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Quote:
Originally Posted by JimN View Post
I donít think it would cause a problem unless you do something drastic- not sure 30 over constitues Ďdrasticí but making it breathe better wouldnís be a bad idea. You could contact Indmar about that.
Thatís a good idea, Iíll email them about it.

Thanks for the advice.
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  #10  
Old 11-04-2018, 07:30 PM
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mikeg205 mikeg205 is offline
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Quote:
Originally Posted by rossi_the_heeler View Post
1100 hours. I got it with 1000.
Too bad you put this much cash into it so far. Plus 2 on the overheat... I presume a complete breakdown and review at machine shop would be the only way to tell....

Too_tall here had his mcx repaired from an over heat. He didnt mention an ecu update.

Maybe a new long block might be more cost effective.


DoubleD you put 2 motors in your 205???

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