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  1. #1
    Vice Admiral tpenfield's Avatar
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    Default Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    I pulled the heads off my 1991 Mercruiser 454 (a.k.a. 7.4L) yesterday. The pistons/cylinders look pretty good, Head gaskets were good, There was some rust on the exhaust ports of the heads on cylinders #4 & #5. Also some rust in the exhaust manifolds of ports #3,#5 & #4,#6. Pics below.

    Engine history=540 hours total over the course of 20 years. Moored seasonally in salt water.

    intakeremoved.jpg100_0498.jpg100_0502.jpg100_0506.jpg100_0512.jpg

    I believe that Cylinders #4 & #5 share an exhaust cross-over port in the intake manifold to help with cold starts (?) (funky square port in the middle of the row of intake ports on the head). Anyway, this area of the intake manifold had serious rust on it when I took the intake manifold off. I am thinking that this was the source of water intrusion into the area of the exhaust ports on the middle cylinders.

    What do you all think? I hope the pictures are helpful.

    I am wondering if this is a typical problem with the 454's of that vintage (Mark IV, 1991). The way the intake manifold meets the cylinder head in that area does not seem to insure a good seal, and would allow the gasket to de-laminate over time.

    BTW - I leak tested both exhaust manifolds, and they are fine. So I am thinking the water is from the crossover port.

    Next steps are to take the valves out of the heads and get a look at the seats. I also have to get the engine mounted on an engine stand so I can have a peek at the lower end.
    Best regards,
    Formula 330 Sun Sport
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  2. #2
    Moderator Bondo's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Anyway, this area of the intake manifold had serious rust on it when I took the intake manifold off. I am thinking that this was the source of water intrusion into the area of the exhaust ports on the middle cylinders.
    Ayuh,... That's an Exhaust passage, not water....

    I'd sooner think the riser gaskets were leakin'...
    I think I see rust near 'em in the 1st picture...
    A pic of the exhaust manifold from the top, instead of from the motor side maybe,..??
    Any Grease is Better,..... Than No Grease at All.......

  3. #3
    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by Bond-o View Post

    I'd sooner think the riser gaskets were leakin'...
    I think I see rust near 'em in the 1st picture...
    A pic of the exhaust manifold from the top, instead of from the motor side maybe,..??
    Here is a picture from the top of the manifolds. I'm not sure it is going to show much. The mating surfaces are OK, but come to think of it, a few years back, I did replace the gaskets. It could have been an issue left over from the old gaskets.

    100_0516.jpg
    Best regards,
    Formula 330 Sun Sport
    Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
    1969 Mercury 7.5 HP Outboard (26346XX)
    .
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  4. #4
    Moderator Bondo's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Ayuh,... The exhaust passages are Rusty,...
    That water got in there, Somehow, Some way...
    Any Grease is Better,..... Than No Grease at All.......

  5. #5
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    From those pictures, the manifolds are junk. The gasket surface (especially on the upper one) is gone. The surface between the exhaust passage and the water passage should be about 1/4" wide and clean shiny metal.
    Don S.


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  6. #6
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Looks like maybe both of those manifold -riser surfaces were leaking.

    If you had a friend with a vertical mill in his home shop you could probably mill all (4) surfaces and get some more life out of them.

    Taking them to a machine shop and having them "chuck them up" on a mill, might approach 1/2-3/4 or more of the cost of buying new when it's all said and done......... and you'd probably want to do all the flat surfaces (ex ports)....... but you'd still have old manifolds and risers with unknown levels of internal rust.


    I would just replace them.

    Sure would be nice if Dry-Joint manifolds and risers were available for the 454......that solves the riser gasket problem once and for all........but I don't think they're available at all for the 454. (good reason to go to a 496!)


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  7. #7
    Moderator Bondo's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Taking them to a machine shop and having them "chuck them up" on a mill, might approach 1/2-3/4 or more of the cost of buying new when it's all said and done......... and you'd probably want to do all the flat surfaces (ex ports).......
    Ayuh,... At My local Machine Shop, they've got a HUGE flat-top belt-sander....
    He turns it on, 'n sets the part, by hand, onto the table for a few seconds, 'n then looks to see the results, continuing til he's satisfied...
    I watched 'im do a set of risers for me,...

    A big vise, 'n a large flat file can be used to some degree of success, dependin' on the operator of the file....
    Any Grease is Better,..... Than No Grease at All.......

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    Senior Chief Petty Officer 04fxdwgi's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Looking at the block and heads, all your cooling passages (especially on the heads) are just about plugged closed. Ya got some work to do on her. Manifolds do look a bit "aged" and could probably stand to be replaced too.
    '92 Chaparral 2550 SX Sport
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    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by 04fxdwgi View Post
    Looking at the block and heads, all your cooling passages (especially on the heads) are just about plugged closed. Ya got some work to do on her. Manifolds do look a bit "aged" and could probably stand to be replaced too.
    Engine and boat are 20 years old, I *could* replace everything . . . maybe I should just get a new boat
    Best regards,
    Formula 330 Sun Sport
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by Bond-o View Post
    Ayuh,... At My local Machine Shop, they've got a HUGE flat-top belt-sander....
    He turns it on, 'n sets the part, by hand, onto the table for a few seconds, 'n then looks to see the results, continuing til he's satisfied...
    I watched 'im do a set of risers for me,...

    A big vise, 'n a large flat file can be used to some degree of success, dependin' on the operator of the file....

    Yeah. I did my old 460 OMC risers and manifolds using my bench type belt sander. but it's a TLAR method at best..... Next time I would mill them on the neighbors C&C mill.
    73 de Rick
    ----------------------------------------------------------------------------------
    I use xxx oil and have never had a problem........
    1987 FourWinns 211 Liberator, 7.4L- Bravo III installed by ME,
    Formerly OMG 460 King Kobra powered
    1947 Stinson 108-2 Station Wagon
    , Franklin 6A-335B. Hartzell CS 2-blade prop
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    Senior Chief Petty Officer 04fxdwgi's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by tpenfield View Post
    Engine and boat are 20 years old, I *could* replace everything . . . maybe I should just get a new boat
    Why were the heads yanked in the first place? Motor is already torn down so see no reason not to try to clean / flush her out on the cheap. That's the course I would take, especially if there were no other problems with her, but now is a perfect time to "refresh" the engine. Mine's 20 years old w/ almost 1300 hours on her and purs like a kitten (knock on wood). My manifolds have surface rust inside (normal) but no blockage at all after the season is done. Haven't pulled the heads, but if engine temp and manifolds are an indication, I'm not going to do till needed.

    Mainifolds aren't really that expensive either, unless you opt for the high end exotic ones. I guess the secret is to flush everything that has raw water running thru it on regular basis (like after every run in crappy water). There are flushing set-ups out there that let you flush it while in the water (I built my own) and it's extra easy with the Bravo having the raw water pump running off the engine.

    PS: If you are junking her, I'll take her off ya hands. Lots of life left in that classic boat.
    '92 Chaparral 2550 SX Sport
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  12. #12
    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by 04fxdwgi View Post
    Why were the heads yanked in the first place? Motor is already torn down so see no reason not to try to clean / flush her out on the cheap. That's the course I would take, especially if there were no other problems with her, but now is a perfect time to "refresh" the engine. Mine's 20 years old w/ almost 1300 hours on her and purs like a kitten (knock on wood). My manifolds have surface rust inside (normal) but no blockage at all after the season is done. Haven't pulled the heads, but if engine temp and manifolds are an indication, I'm not going to do till needed.

    Mainifolds aren't really that expensive either, unless you opt for the high end exotic ones. I guess the secret is to flush everything that has raw water running thru it on regular basis (like after every run in crappy water). There are flushing set-ups out there that let you flush it while in the water (I built my own) and it's extra easy with the Bravo having the raw water pump running off the engine.

    PS: If you are junking her, I'll take her off ya hands. Lots of life left in that classic boat.
    The heads were pulled off because Cylinders 3,5 and 4,6 were showing 35 - 50% leak on a cylinder leak test. It proved to be the valves - some intake and some exhaust. Once things were opened up, the manifold/riser issue was discovered. It definately effected the exhaust valve on #5. I have not torn down the other cylinder head yet.

    My plan is to do a valve job and get things back together. The engine only has 540 hours, so it has got some good life left in it.

    I am looking to sell the boat at some point and move onto a bigger boat. I'm not sure just when all that will happen.
    Best regards,
    Formula 330 Sun Sport
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    Moderator Bondo's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    My plan is to do a valve job and get things back together. The engine only has 540 hours, so it has got some good life left in it.
    Ayuh,... from yer pictures, 'n descriptions, I don't see any reason to go deeper...
    Any Grease is Better,..... Than No Grease at All.......

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    Senior Chief Petty Officer 04fxdwgi's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by Bond-o View Post
    Ayuh,... from yer pictures, 'n descriptions, I don't see any reason to go deeper...
    If motor was still in boat, I would agree 100%. But since it's sitting on the floor already, why not pop off the pan, and plastigauge the bearings, replace the 20 year old timing chain cover and pan gaskets and seals, front and rear seals on the crank, check the timing cover / pan for any rust problems, clean out some of that scale in the cooling passage holes and check the timing chain. Put it all back together after a clean bill of health (or replace anything that is marginal) and paint her up like new. Getting motor out and back into boat is the hard part.
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    Petty Officer 3rd Class grendelsniper's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    That is a great idea, the last thing you need is to put it all back in and break a timing chain or find some kind of oil leak that was caused when the motor was out and seals where disturbed. agree 100%.

    Quote Originally Posted by 04fxdwgi View Post
    If motor was still in boat, I would agree 100%. But since it's sitting on the floor already, why not pop off the pan, and plastigauge the bearings, replace the 20 year old timing chain cover and pan gaskets and seals, front and rear seals on the crank, check the timing cover / pan for any rust problems, clean out some of that scale in the cooling passage holes and check the timing chain. Put it all back together after a clean bill of health (or replace anything that is marginal) and paint her up like new. Getting motor out and back into boat is the hard part.
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    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by tpenfield View Post
    I pulled the heads off my 1991 Mercruiser 454 (a.k.a. 7.4L) yesterday. The pistons/cylinders look pretty good, Head gaskets were good, There was some rust on the exhaust ports of the heads on cylinders #4 & #5. Also some rust in the exhaust manifolds of ports #3,#5 & #4,#6.
    Next steps are to take the valves out of the heads and get a look at the seats. I also have to get the engine mounted on an engine stand so I can have a peek at the lower end.
    UPDATE and a question . . .

    I have the heads torn down. Still trying to get the last remnant of the head gasket off of the head and block.

    I took another look at the exhaust manifolds and elbows, based on the comments so far. The exhaust manifolds are not so good, but the elbows are ever worse!!! Soooo, I have eye-balled a full replacement set - GLM brand - for about $610. (such a deal)

    There is one exhaust port on each cylinder head where the valve seat is pitted and needs to be replaced. Everything else looks fine and can be freshened up with some grinding or lapping. I was able to remove one of the seats so far and I'll probably remove the other one tomorrow.

    Question: I'm having a little bit of trouble locating the correct valve seat replacement part. I have searched quite a bit online and have not found what appears to be the correct one for this engine ( GM/Chevy Gen IV 454 oval ports). This is a 1991 Mercruiser 7.4L (330 HP). I have found some Exhaust valve seats online, but they appear to be for aluminum heads and measure 2.000 Inches OD. It looks like the exhaust valve seats on my engine are about 1.80 inches +/- OD and 1.5 inches ID. (Iron Cylinder head)

    Any advice/sources for valve seats (aka valve seat inserts)? Amazon lists a bunch, but I have not found the proper one or even information to cross-reference between the different brands of valve seats, etc.

    TIA
    Best regards,
    Formula 330 Sun Sport
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  17. #17
    Chief Petty Officer picklenjim's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Those heads are also known as 454 peanut port heads. They are the smallest head Chevy made for the 454. Their also the most availiable. I never heard of anyone replacing a valve seat in one. It's just not worth it. Probably why you can't find any. The thing to do would be to just find another head to replace it. Would probably be cheaper. They were used in most 454's that were in cars and trucks. Look for the casting number between the springs.

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  18. #18
    Senior Chief Petty Officer 04fxdwgi's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by tpenfield View Post
    UPDATE and a question . . .

    I have the heads torn down. Still trying to get the last remnant of the head gasket off of the head and block.

    I took another look at the exhaust manifolds and elbows, based on the comments so far. The exhaust manifolds are not so good, but the elbows are ever worse!!! Soooo, I have eye-balled a full replacement set - GLM brand - for about $610. (such a deal)

    There is one exhaust port on each cylinder head where the valve seat is pitted and needs to be replaced. Everything else looks fine and can be freshened up with some grinding or lapping. I was able to remove one of the seats so far and I'll probably remove the other one tomorrow.

    Question: I'm having a little bit of trouble locating the correct valve seat replacement part. I have searched quite a bit online and have not found what appears to be the correct one for this engine ( GM/Chevy Gen IV 454 oval ports). This is a 1991 Mercruiser 7.4L (330 HP). I have found some Exhaust valve seats online, but they appear to be for aluminum heads and measure 2.000 Inches OD. It looks like the exhaust valve seats on my engine are about 1.80 inches +/- OD and 1.5 inches ID. (Iron Cylinder head)

    Any advice/sources for valve seats (aka valve seat inserts)? Amazon lists a bunch, but I have not found the proper one or even information to cross-reference between the different brands of valve seats, etc.

    TIA
    On the valve seats, try the speed shops, for example: http://www.summitracing.com/parts/TFS-41400272-8/
    If you don't see what you want right away, give them a call. Jegs is another good source, or just have the local machine shop do a valve job on the heads. They'll regrind the seats, but if too far gone they'll replace. They do it every day. Or, you can purchase new heads at Jegs or Summit in any flavor you want.
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  19. #19
    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Just an update on this thread, since it has been a while. . . I'll post some pictures as well. . .

    Problems/Issues found:

    Rusty/pitted valve seats on #4 exhaust and #5 exhaust. I had a machine shop install new valve seats and grind the valves. The other valves were good so just some manual grinding to freshen them up.

    I found substantial amounts of iron sediment in the water jackets on the engine block. I popped out the core plugs (aka freeze plugs) and removed all the sediment with a power washer, etc. The machine shop said that the areas in between the cylinders were running hot, based on looking at the heads. Probably the sediment had something to do with that.

    Bottom end of the engine checked out good, little/no wear, so I left it alone.

    The timing chain looked a little sloppy, plus the cam sprocket was the kind with nylon teeth. so, I replaced it with a Melling high performance set.

    I'm still waiting for the marine head gasket kit (on back order) so I can re-assemble the heads. Meanwhile, I am taking care of lots of rusty parts with Naval Jelly and POR-15 engine enamel.

    I'll post some pics later on . . .

    OK, here are some pics . . .

    100_0527.jpg100_0573.jpg100_0574.jpg100_0580.jpg100_0604.jpg
    .
    Best regards,
    Formula 330 Sun Sport
    Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
    1969 Mercury 7.5 HP Outboard (26346XX)
    .
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    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Here are a few more pics . . .

    100_0631.jpg


    100_0658.jpg100_0669.jpg100_0673.jpg


    I'm still waiting for some gaskets and related parts to arrive so that I can re-assemble the heads.
    Attached Images Attached Images
    Best regards,
    Formula 330 Sun Sport
    Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
    1969 Mercury 7.5 HP Outboard (26346XX)
    .
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by tpenfield View Post
    Just an update on this thread, since it has been a while. . . I'll post some pictures as well. . .

    Problems/Issues found:

    Rusty/pitted valve seats on #4 exhaust and #5 exhaust. I had a machine shop install new valve seats and grind the valves. The other valves were good so just some manual grinding to freshen them up.

    I found substantial amounts of iron sediment in the water jackets on the engine block. I popped out the core plugs (aka freeze plugs) and removed all the sediment with a power washer, etc. The machine shop said that the areas in between the cylinders were running hot, based on looking at the heads. Probably the sediment had something to do with that.

    Bottom end of the engine checked out good, little/no wear, so I left it alone.

    The timing chain looked a little sloppy, plus the cam sprocket was the kind with nylon teeth. so, I replaced it with a Melling high performance set.

    I'm still waiting for the marine head gasket kit (on back order) so I can re-assemble the heads. Meanwhile, I am taking care of lots of rusty parts with Naval Jelly and POR-15 engine enamel.

    I'll post some pics later on . . .

    OK, here are some pics . . .

    100_0527.jpg100_0573.jpg100_0574.jpg100_0580.jpg100_0604.jpg
    .
    Good job, exactly what I would have done. The new timing gears will give you a little piece of mind, being redone with steel gars instead of the plastic. Will make a little more noise, but you won't notice it. IMHO. New freeze plugs, gaskets and she'll be like a new motor. Taking it out was 80% of the job and the refresh was peanuts compared to doing it again.

    Now wait for the next boating season and enjoy........ BTW, I'm origionally from the South Shore, myself.
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  22. #22
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Hi Ted, nice work, looks like your on the downhill side! Did alot of material come out with the power washer and how did you leak test the heads? Great boat website too!

  23. #23
    Vice Admiral tpenfield's Avatar
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    Default Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Quote Originally Posted by vi View Post
    Hi Ted, nice work, looks like your on the downhill side! Did alot of material come out with the power washer and how did you leak test the heads? Great boat website too!
    Yes, a whole lot of iron sediment came out of the engine block with the power washer. I did not really have any way of measuring it, but I would say that the water jackets were about 1/3 -to- 1/2 full of the stuff. I initially tried to get some of it with just a screw driver, but it really needed to be blasted and flushed out. The cylinder heads had relatively little, as the iron would tend to settle at the bottom of the water passages.

    I used a 'leak test' gauge (OTC #5609 I think) for the leak testing and I ran 60 psi. My web site has a picture of the gauge in one of the 'rebuild' pages. Keep in mind that the compression test looked OK with only +/- 5% difference between the cylinders. Going forward, I think that I will always do a leak test in addition to a compression test.
    Best regards,
    Formula 330 Sun Sport
    Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
    1969 Mercury 7.5 HP Outboard (26346XX)
    .
    My Formula 330SS Web Site: -> Link
    My Formula 242SS Web Site: -> Link
    My Catalina 22 Web Site: -> Link

    Member of the Month - February 2013 http://www.iboats.com/blog/tpenfield...-of-the-month/

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