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AQ170 falls on its face past half throttle

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kevinmi

Contributing Member
Hi guys. I have a 1976 bayliner liberty 2150 hard top (aq170/280). I have put a lot into it and have been using it for the last 7 years or so. Got it out this year and really was not having any issues. I could get on plane and go 25mph with 4200 rpms. recently though, i have been having problems. i cant go past half throttle (3000rpms) with out it sputtering. Im noticing the temp gage is hotter than i remember. I changed my fuel separator and that didnt seem to help. I adjusted my timing (rotated my distributor) and that didnt help. I am noticing a lot of white smoke coming out of the hole in the valve cover when i took off the air filter or spark arrester (whatever that thing is called). I am also noticing a lot of oil around the carberators (im assuming its coming from that rubber thing sticking out of the valve cover). I also am noticing white smoke coming from the dipstick hole. I am pretty sure thats not supposed to do that. it idles fine and in neutral, the engine revs great. we pulled each plug wire while in idle and it sounds like they all are atleast firing. The back of my boat is not black like it would be if unspent fuel was going out the exhaust. I think its probably just old, tired and needs to be rebuilt but my brother thinks it may be something simple. any ideas would be greatly appreciated.
 
yep the oil looks as it should aside from being all over. I was in there today doing some work on a sticky lift pump. i noticed a lot of oil under the motor.
 
Oil in the carb is worn piston rings allowing compression gas past the piston into the oil pan and then blowing it up the passage way to top of engine. Brown oil and white vapor could be water getting in. Do a compression check .
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the plugs and wires are about 2 years old. I switched it to an electronic ignition a few years back (pertronix). It does sound like a spark knock when i try to go past half throttle. maybe you guys are right. maybe just new plugs and wires and a good clean up. I will get in there tomorrow and check the plugs and compression if i can find the compression gage. thanks guys! -kevin in michigan
 
i finally got around to doing a compression test and assuming the gage is correct, i have cylinders ranging from 115psi to 150psi. is that acceptable? i went ahead and put new plugs in as i really dont know what the difference between a bad plug and a good plug is. I am thinking of changing the wires again. it seems last time i just went to autozone and got a 70s era ford truck straight six set.
 
well it looks more and more like its compression. i tested it again with a brand new 40$ compression tester and im averaging 60-90 psi. that, coupled with the oil in the spark arrestors is pointing more and more to blow by. a friend of mine suggested checking compression then squirting a few squirts of oil into the cylinder and checking it right after.. he said if the compression increases by 20 or so, its the rings, other wise its valves. im not holding out much hope tho i will try that. on a side note, I contacted a marine engine builder here in michigan about getting my aq170 swapped out or possibly rebuilt and he said he needed to consult with an expert about it.. he said "he lives in oregon". i asked if his name was rick lol. apparently rick is the worlds foremost expert on this ole engine of mine! hopefully i can get someone to rebuild this thing as it seems like swapping it out is going to be just as hard. im most worried about parts like pistons and rings. thanks a ton for all of you guys help! -kevin in michigan
 
I'm going to be a shameless opportunist here and say.. Have I got an engine for you! It's on eBay. Open to offers. It purrs. No smoke. Great compression. Starts cold like flipping a switch. I have a virtually brand new reman about to come home from the machine shop. Haven't decided how far to take it. Short block, long block or complete stem to stern? The choice is yours. PM if you're interested.
 
The rings on the old 130/170 engines were known for going South. I even had a 170 in my own boat that the rings were shot in but I still used it. Once we started it we would use it as much as we wanted to on that start up and never shut it down, as it was a bitch to get it restarted because of low comp. We even had to raise the drive up some in the water as the engine couldn't push all the exhaust and water out lowered all the way to start it. We had a blast but didn't turn it off. When we did shut it down we had to wait until it cooled for the comp to come back up. Those were the days. The cast iron head engines were great engines and I wouldn't be afraid to still have one today. One must remember though that these engines were designed to run on very good gas and not that cheap stuff we're using today. If you do rebuild make sure to use the thickest head gasket you can get which should be the "c" engine gasket. The one on ebay seems to be legit as it is COMPLETE and we all know what the old parts are worth.
 
boatdoc55 said:
The rings on the old 130/170 engines were known for going South. I even had a 170 in my own boat that the rings were shot in but I still used it. Once we started it we would use it as much as we wanted to on that start up and never shut it down, as it was a bitch to get it restarted because of low comp. We even had to raise the drive up some in the water as the engine couldn't push all the exhaust and water out lowered all the way to start it. We had a blast but didn't turn it off. When we did shut it down we had to wait until it cooled for the comp to come back up. Those were the days. The cast iron head engines were great engines and I wouldn't be afraid to still have one today. One must remember though that these engines were designed to run on very good gas and not that cheap stuff we're using today. If you do rebuild make sure to use the thickest head gasket you can get which should be the "c" engine gasket. The one on ebay seems to be legit as it is COMPLETE and we all know what the old parts are worth.
Click to expand...

So nice to read those words. These ARE great engines. This is my first boat at 56 years of age. I drive a Jeep with a straight six. I have a 51 Ford with a straight flathead six. When this boat came along and had a straight six I said.. That's my boat! A 22' Fiberform cuddy cabin cruiser. I was annoyed as I went to the forums for assistance to constantly read posts in which people were being told that these engines are old garbage and should be replaced. Sure they're old. 40 years of dependable service and you'd be tired too! I've got a refreshed AQ170 in my boat which I just took out for a sea trial yesterday. Pulls like a quarter horse out of the gate. 30MPH at 3000 RPM. Can't wait to see what she does flat out on good gas. That was using farm gas! As low an octane as it gets. I forgot to take my methyl hydrate along to boost the octane. As I searched for parts for my own engine I had a chance meeting with a fellow who had a shop full of engines and outdrives. I went crazy and bought the lot. Hence the motor on eBay. I could make more by parting it out but it's too nice to tear down! I want it to find a good home in another great old boat like mine.
 
my problem is that it actually runs great now. just has low compression. if its just the rings, maybe im better off just replacing them.... if i can find parts that is. i have a siezed 170 in the garage that came with the boat. i have no idea the condition of it but i figure there is something on it i can use. I found a guy local that has a "project boat" with the same motor for sale. I just put a ton into this thing. all new glass and a brand new kicker for me to start over.
 

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kevinmi said:
my problem is that it actually runs great now. just has low compression. if its just the rings, maybe im better off just replacing them.... if i can find parts that is. i have a siezed 170 in the garage that came with the boat. i have no idea the condition of it but i figure there is something on it i can use. I found a guy local that has a "project boat" with the same motor for sale. I just put a ton into this thing. all new glass and a brand new kicker for me to start over.
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It sure sounds like rings. The bottom end on these engines is rarely an issue. I'd take the head off and get it re-manufactured ($300). Re-ring ($65) after honing the cylinders. Put it back together and you'll be good for many seasons. The rings are inexpensive and available. Head gaskets unfortunately, are expensive ($200 ). Well worth the effort and expense though.
 
Kevin, if I may.....

When you adjust the ignition advance, please do not do this without a good timing light nor without your OEM specs in front of you.
Set the BASE advance, but also check to see what the "progressive" and "total" advance are doing.

Not enough "progressive" and "total", and the engine will suffer performance.
Look at the advancing system flyweights and flyweight return springs.... all must be free and in good working condition.

Too much "total" and if too early....... the cylinders may undergo detonation, and that can cause serious engine damage. :mad:




When you take the cylinder pressure readings, understand that the pressure may be accumulative...... meaning that you want to cycle through several compression strokes.
This means that you will crank the engine over approx 7 revolutions per cylinder reading.
Don't worry.... the gauge will read only the Max pressure produced within the cyllinder.

Do this with all spark plugs removed.


.
 
I switched to pertronics a few yrs ago. It made a huge difference. I noticed the rotor was a little loose. That wouldnt cause low compression though would it? It starts up great, idles great and screams when in my driveway. I get it on the water and after 3k rpms, it spits and sputters. Last time I went out we tried turning the distributor and listening for improvement. Either direction just made it worse. I really havent messed with the ignition since I put that kid in a few yrs ago.
 
IF, you end up re-ringing it, make sure the shop that hones it for you puts the proper finish on the walls. When I was rebuilding the 130/170's in the early 80's we would use DEEVES rings and only cast iron. We knew these would seat well and not have a problem. Will they last as long, no but long enough. The OEM rings were iron rings also.
 
This is what I got with a nice new pressure gage just the way rick said to do it. I checked again after I squirted a lil oil in each cylinder. compression before oil then add oil
cyl 1:110 120
cyl 2:70 80
cyl 3:100 105
cyl 4:105 110
cyl 5:80 100
cyl 6:75 80

Thankyou all for your help. I took ur advice and did some calling. Found a guy to remanufacture the head. He said he would rebore and redo the whole engine for about 2500. Thats a lot of $. I think heads, rings,gaskets,hone might be the way to go.
 
Well, im past the point the point of no return. I ripped all the electrical and fuel systems off. Unbolted the bell housing and I got one bolt left before I take the whole thing out. Kind of exciting but a lil scary. I'll post back with pics after I bend a 9/16 wrench at work tomorrow to get that last bolt off. Thanks again guys
 
I suppose that you did not perform a cylinder leak-down test..... yes/no???
That would have given you an idea as to piston rings and/or valves being the culprit.


Only if you can source new first over pistons:

The 170 is a push rod engine..... so be sure to keep all of the cam followers in order so that that they will go back onto the same cam lobes.

Tear this down yourself, and then take the cylinder block to your machine shop.
Have them clean and prep the block for boring.
They will need to have the new pistons.

Make sure that they have the old connecting rods, and have them install the new pistons on them.

Have them re-do the cylinder head also.

The rest will be nothing more than re-assembly and you will have cut your costs down dramatically.
 
cylinder leak down test? i did the "check then squirt oil in and recheck" test. not sure if thats what that is called. the results are posted above. i have to wait till this wkend to take it into work and pull the motor. as tom petty once said "the waiting is the hardest part". my tentative plan is to take it apart and get the head remanufactured, have the same guy hone the cylinders then. put it back together with new rings and maybe some new bearings... unless i can get the engine guy to give me a deal, in which case, just have him do the whole thing. he is checking on parts and such and said he would call me back... they all say they will call me back lol. ill give him another day as i really cant do anything till saturday. man the fish are biting and the water is nice.
 
kevinmi said:
This is what I got with a nice new pressure gage just the way rick said to do it. I checked again after I squirted a lil oil in each cylinder. compression before oil then add oil
cyl 1:110 120
cyl 2:70 80
cyl 3:100 105
cyl 4:105 110
cyl 5:80 100
cyl 6:75 80

Thankyou all for your help. I took ur advice and did some calling. Found a guy to remanufacture the head. He said he would rebore and redo the whole engine for about 2500. Thats a lot of $. I think heads, rings,gaskets,hone might be the way to go.
Click to expand...

You've got all the options now. The hard part is deciding which is money Best spent. Suggesting a re-bore on an engine that hasn't been disassembled might be a bit premature. Hopefully it just needs de-glazing and a new set of rings. I just did the same job on mine and it's running like new.

Just saw a 'runner' on eBay claiming low hours and selling for $1000! The exhaust manifold and a couple of other parts will sell for that much on a good day. Part out your existing engine and you might end up out of pocket very little.
 
Make sure that head on the 170 is "magged" before any other work. They and the 130 were known to crack between the seats. I do hope your block can just be honed and ringed.
 
a little bit of good news... in prepping for removing the engine this wkend, i noticed something. the junk engine in my garage is aq170b. i just assumed that the one in the boat was too. It is not. it is aq170c. I think that this really doesnt mean much but in spec'ing out part #s for the gaskets and such, i saw they use different ones. this one only costs $105.99! the "a" and "b" ones were over $200. I know im reaching for some good news but ill take it at this point. I got it all disconnected but cant seem to seperate the engine from the drive. Maybe it will come apart when i start pulling up on it with a hoist. thanks again for all u guys help. I will be pulling it out this wkend if all goes well.
 
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kevinmi said:
a little bit of good news... in prepping for removing the engine this wkend, i noticed something. the junk engine in my garage is aq170b. i just assumed that the one in the boat was too. It is not. it is aq170c. I think that this really doesnt mean much but in spec'ing out part #s for the gaskets and such, i saw they use different ones. this one only costs $105.99! the "a" and "b" ones were over $200. I know im reaching for some good news but ill take it at this point.
What parts are you refering to?
Go here.... and see if you can find the differences between the B and C engines.


I got it all disconnected but cant seem to seperate the engine from the drive.
How are you planning to pull the engine?
With the flywheel cover attached.... or by seperating the engine from the flywheel cover???

Maybe it will come apart when i start pulling up on it with a hoist.
Do not force anything to come apart.
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kevinmi said:
cylinder leak down test?
This involves pressurizing each cylinder with a leak-down tester that will allow us to measure the air loss.
Also allows us to:
a..... look at the differential in air supply -vs- air pressure within the cylinder given any loss.
b..... determine where the air loss is (i.e., piston rings, valves, and/or cylinder head cracks, etc.)


i did the "check then squirt oil in and recheck" test.
Intrinsically, any amount of oil in a cylinder will increase cylinder pressure simply by way of the volume that the oil occupies.
The goal with the oil-in-the-cylinder, is to aid in sealing the piston rings as to either point to them, or to eliminate them as being the culprit.

my tentative plan is to take it apart and get the head remanufactured,
As Gary suggested, have them clean and magnaflux the casting.

have the same guy hone the cylinders then. put it back together with new rings
Make certain that all pistons can go second time around.


and maybe some new bearings...
Definitely new bearings and seals.
Click to expand...
 
i attached pics of the head gasket highlighted. for some reason it is a different part # (aq170c-3855409,aq170b-461056). I unbolted the starter and all of the bolts holding the flywheel case to the intermediate or whatever that thing is called. i took the 4 bolts off of the lower inspection plate as well. i couldnt seem to get it to pull away from the outdrive, but i was doing it by hand. i couldnt really pull up on it and pull away effectively. tomorrow i will wheel an a frame over it and hook a winch up. that should ease things quite a bit. i will try my best to be gentle.
 

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If you haven't pulled your motor yet, I had a similar problem. I have twin 170's. I switched to Pertronix also. What a difference. But I had the same problem with my port motor. So I pulled the distributors and had the checked out, springs/weights, etc. When I replaced them, I did not put them back on the same motors. Now my starboard motor was not working well on full throttle. It was a bad magnet in the the Pertronix part that goes in place of the points. I had another set for any future problems. Replaced that and back to normal. I would have a shop check out that black rotor part first, may be that, not that you don't need to ring it, but may still crap out once you do all that work. Stymied me for a while!
 
good call suds. i thought about that and have a second pack just in case. i should have tried it. i do know i have low compression though so it was inevitable. i will definately keep that in my back pocket if it goes back together and has similar problems. As of an hr ago the motor was sitting in the back of my truck. one thing i noticed though was i damaged that gasket between my bell housing and my engine. i went to look up the part # and all it says is "obsolete part" its aq170/280. that troubles me a little but ill keep looking. thanks again guys. i wouldnt have even tried this if not for your support.
 
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