AQ170B failed camshaft advice sought

gerrshel

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Sep 17, 2009
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Looking for advice on a 1973 AQ170B ... it appears the camshaft has failed, the #1 exhaust push rod is barely moving up/down. At this point I have the spark plugs, valve cover and rocker arm removed. Compression is good in all cylinders... (guessed that it had blown a head gasket when it happened, doesn't appear so.)

Is it possible for a cam lobe to fail instantly?
Was running fine all day with several stops, started up to head for home and heard sort of a pop and then obvious problem ... made it to the ramp but wasn't pretty or quiet ... what sounded like a compression leak turned out to be #1 cylinder decompressing thru intake/carb as the exhaust valve was evidently not opening ...

Is there any chance that the lifter could be at fault somehow? The pushrod looks straight and undamaged. The head will need to come off next to see more.

Can the camshaft be removed/replaced with the engine in place coupled to the outdrive? Or is there need to get at the rear of the block? Plenty of room in the boat as the doghouse pulls out of the way ...

There is a new listing for a cam on Ebay today oddly enough and only about 20 miles from me, .... however, with a gasket set etc. I am thinking is probably time for the scrapyard ... rest of the boat seaworthy but nothing special ...

thanks in advance for any advice/ answers
 

Saline Marina

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Don't know the engine in question but a failed lifter would cause a lack of lift that you experience. But I think you'd hear instant ticking/knocking from the backlash in the system. Its possible the nose of a cam lobe fractured off, could be from poor metallurgy or poor lubrication.
 

HorizonblueDK

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I have a new AQ 170 lifter laying on my desk. It is hollow and seems to be made from two pieces welded together and then machined. It is therefore possible that this can fail/break, if a crack in the welding has developed over time. I would say, take off the cylinder head and inspect to see what is wrong. It is an old engine and easy to work on and it doesn't run anuway. Dismantling doesn't cost anything. And then you can draw conclusions.
 

Walt T

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I would tend to agree on a lifter failure. Popping through intake means an intake valve problem. If the exhaust valve doesn't open some of the combustion gasses will blow through the intake valve when it opens but it would run so badly and would not idle since that piston would have two compression strokes. I imagine the exhaust valve is opening slightly. Can also be a bent pushrod due to valve train damage elsewhere. Camshafts usually don't fail by themselves. It's usually a lubrication failure as Saline Marina says. What kind of name is that anyway? Saline Marina? What you got a lake a bunch of doctors filled up with saline? Sorry, couldn't resist.
 

jerryjerry05

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Measure the push rod against another one.
Going back to my old Caddy days.
They were famous for push rods wearing down.
I had 3 different Pontiacs that were ticking.
Removed the covers and took the rods out and measured.
They were as much as 1/8in short.
The rocker(U don't have) was worn too.

Saline isn't that a place in America? Saline,Mi. Yes Canadians are Americans too.
 

gerrshel

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thanks for the answers folks .... I will remove the head just out of curiosity and have a look ... love to make it run again I doubt it will make sense $$wise to make it go again, even if it was a few junkyard parts ... thinking it has become some of those junkyard parts ... I took a bunch of photos for a craigslist ad ... I'll put up my findings when I get there ... good time of year here to buy a boat ...

for the record ... it did run reeeaaall poorly 12 miles to the ramp ... made it but it was ugly, definitely discussing who we might call as the sun goes down .. never overheated .... if I had that crystal ball I would have pulled #1 spark plug
 
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Walt T

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I have a few doctors that want to remove my head and examine it just out of curiosity. Gee I hope they wait until I'm dead.
 

Saline Marina

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Saline is near Ann Arbor which is more famous. I'm at least 20 miles from any lake and live amongst the cornfields. There is a mythical saltwater spring around here somewhere that gave the town its name in the 1800s and has never been seen since.

Its sort of a joke because there's obviously no marina here, I know a little about gasoline pushrod engines but nobody in my family owns a boat except for me at the end of this summer...so while I have some skills in maintenance and machine repair I have a long way to go in learning about the "water stuff".
 
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jerryjerry05

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I lived in Durand, Mi. and the salt deposits were out in the woods behind the house.
Under Detroit is a big salt mine.
 

gerrshel

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well the head is off ... the cam did indeed wipe the #1 exhaust lobe off .... looks to be quite round looking thru the hole where the lifter fits. lifter is a hollow solid piece, looks as good as any of the others... Sure went all at once when it did it! Don't have ambition to go any further with disassembly, officially looking for a new boat. Listed on craigslist as AQ170B/270 parts: http://spokane.craigslist.org/boa/4699461372.html ....from there it's off to the scrapyard ...
thanks for the answers
 

PiratePast40

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If you don't get any local offers, might want to try ebay. If in good shape, that exhaust mainifold is worth a pretty penny. Carbs and lift mechanism are getting harder to come by and fit other engines. Oil cooler is another component that is in demand. Would hate to see that stuff go to a junk yard when the parts are getting scarce.
 

gerrshel

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the boat and trailer went off to a salvage guy yesterday ... he is on ebay as gcbones2 if anyone is interested ... bittersweet but time to find a new boat ...
 

PiratePast40

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Thanks for sending it to a salvage yard instead of the trash. Components are getting hard to find and keeping them in circulation helps all of us out.
 

gerrshel

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Sep 17, 2009
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there way too many good parts to just throw away ... always a fan of a boneyard!! note that I gave him the extra set of carbs on a manifold as well, plus 3 carb kits minus the top gasket, stole those when looking into the ones on the engine...
 
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