Mercruiser 470 3.7L - replacing exhaust elbow & shutters and got unpleasant surprises

Blueghost924

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Mercruiser 470 3.7L - replacing exhaust elbow & shutters and got unpleasant surprises

Well, I've finished up a lot of the electrical wiring, and now I've shifted to the exhaust system. This is an engine I bought earlier this year and installed recently - and I knew the exhaust elbow and shutter needed to be replaced. Well, this afternoon I removed the exhaust elbow and didn't quite like what I saw. First, there was a little more rust and silt than I expected. Second, the 2 longer bolts snapped off at the base as you can see in one of the pictures. Third, it looks like the antifreeze passages are clogged? I've included a pic of the shutter retaining bar - yup the actual shutter is gone.

For the long bolts that snapped off at the base - advice on removing the stubs?

For the antifreeze passages that appear to be clogged - advice? My first thought is a shop vac while using a Dremel tool to drill away the blockages.

I've included a picture of the old exhaust elbow as well.

exhaust 1.jpg
exhaust 2.jpg

exhaust 3.jpg

exhaust 4.jpg
 

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Bt Doctur

Supreme Mariner
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Aug 29, 2004
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The A/F side of the exaust manifold is supposed to be sealed off with a blockoff plate.
Best way is to grind the stubs flush, center punch, drill and re-tap to the correct size.
Untitled4jpg_zps620a1fc6.jpg
 
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Blueghost924

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Thanks for the reply Bt Doctur - helpful diagram. One interesting note - it seemed as if when I pulled off the exhaust elbow, there was a small amount (like a little dribble) of antifreeze. I wonder if one of the sealed areas has a pinhole or very small leak?

Any advice on removing the old bar from the shutter reminent and installing the new one? Looks like the old is riveted in there.
 

Blueghost924

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One note: The Mercruiser water shutter part 45586 that I recently bought is oval shaped, but from what I've seen from reading all Mercruiser water shutters are oval. I put the new water shutter against the top of the exhaust pipe just to eye ball the fit, and the exhaust pipe top (where the old shutter bar is still in place) is round. Not oval. I made a call to the company, and they explained that it's supposed to be that way, and that there will be a slight "gap" around where the oval water shutter and the round exhaust pipe surfaces don't quite come together cleanly.

Also, it appears as if the ID of the exhaust pipe top is approximately 2 7/8" (roughly). This may be the wrong fit water shutter.

Does this make sense?
 
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achris

More fish than mountain goat
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May 19, 2004
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The shutter lies in the pipe at an angle, hence the oval shape. What is the serial number of your engine. I'm seeing different parts for different years, so at this point can't tell if the shutter is the right one. Early ones have a single plate on a shaft, later ones have the split shutter...

Chris.........
 

Blueghost924

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Hey Chris - thanks for the reply and sorry about the delay. The original engine serial that came with the boat is A409012. I say original because I know that my current Mercruiser 470 is not the original, and the scrap one that came out may not have been as well.

Here's a picture of the top of the current lower exhaust pipe:
20141115_182145_resized.jpg

The guy I bought my current Mercruiser 470 also gave me a space lower exhaust pipe, which looks like this:

20141115_182651_resized.jpg

20141115_182637_resized.jpg

Ironically enough, the Mercruiser exhaust flap part 45586 fits nicely in this spare exhaust pipe that I got as a freebie. Also, in my boat, the lower exhaust rubber boot that I removed is Mercruiser part number 32-90949...if that helps.

Thanks!
 

achris

More fish than mountain goat
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Messages
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That exhaust boot was only used in 83/84 470s, and the correct shutter for that year was a split shutter, -60930... Do you have a photo of the profile of the exhaust pipe (more side on than looking straight down it), and is there another pipe between the one with the shutter and the end of the elbow?

Looking at the photo of the elbow in the first post suggests you have an earlier exhaust system, but the boot number you quoted is for the later ones... You may well have something we call a 'FrankenMerc'... Finding the right parts can be extremely difficult in these situations. Generally the only person who will know for sure what is used where is the maniac who set it up in the first place, and this is precisely why I vehemently hate it when people do this sort of thing (and I'm being extremely polite!).... Keeping things as close to original is the only real way to make sure it's an easily maintained machine for the future (with the possible exception of changing a points ignition to some form of electronics, usually Pertronix).

Chris.........
 
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Blueghost924

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Thanks Chris - and great term...FrankenMerc :laugh:.

I've laid out all the parts in my current exhaust configuration that lead up to the lower exhaust pipe, and here's what it looks like:

20141124_190128_resized.jpg

The Mercruiser part numbers for each from top (exhaust elbow) to bottom is:

76325
70981A3
42423
32-90949

I tried to get a picture of the lower exhaust pipe, but just couldn't get a good one (at least, one that is sensible). It looks like the lower exhaust pipe bends down and to the left (as viewed from the top back port corner of the engine).
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Yep, definitely a FrankenMerc. The exhaust elbow is from the 82 and earlier model and the rest of the exhaust is 83 and later. So, for the right shutter, you are going to need the later ones (they fit in the exhaust pipe after your '32-90949'.... And the number for them is -60930.. You can even get them here, at iboats (remember to ask for your 5% discount as a forum member).... http://www.iboats.com/Search/dm/?ke...t.y=12&cart_id=797361412&session_id=132454959

Chris.......
 
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