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Options for older AQ170

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dock_holiday

Contributing Member
"Hi all, new guy here on the b

"Hi all, new guy here on the board. I have an older AQ170 on a 270 in a boat I recently bought. I knew the motor was tired but I got the boat cheap...I think...I guess we will see. Dry and wet compression tests show that all cyls are at 125-150 dry except #3 it's at 40 dry. Wet tests shows a 20-25 PSI increase in all cyl's which brings #3 up to a whopping 60 PSI in the wet test. Looks like at least one bad valve in #3 right? When it's running there is a lot of crank case vent vapor coming out the elbow on top of the valve cover (no side vent on the block as there is on the older 4 cyl models) ...so much so that the vapor was fouling the plugs as it was sucked back into the intake as set up OEM. I have fixed the fouling problem by rerouting the vapor out to the atmosphere through the transom. The motor makes enough power now for my needs as the boat can pull my kids on their tube faster than they care to go for now. Eventually I will have to replace or rebuild the motor. Will running it as is on 5 cyl's make it die sooner? I have heard that "any volvo 4 cyl motor will bolt right up to the bell housing" I am suspicious that this is not quite true. I suspect that the older AQ 130 would probably work, but what about a newer OHC AQ131? Anything with more power than the 131 make a good swap onto my 270 drive? I quess the other option is to rebuild or replace the head on the 170 and see how much longer the lower end holds together. What do you guys think? I would really appreciate any thoughts/advice/wisdom on the situation.
Thanks
Matt"
 
"<font color=""ff0000"">"W

"<font color=""ff0000"">"Will running it as is on 5 cyl's make it die sooner?"</font> Don't even think about running on 5 cylinders.

<font color=""ff0000"">I have heard that "any volvo 4 cyl motor will bolt right up to the bell housing"</font> It will, but the gear ratio in the outdrive lower gear unit for a 4 cylinder is 2.15:1 and for a 6 cylinder is 1.89:1. And replacing gears ain't cheap. If you want to install a 4-cylinder, it would be probably cheaper to go to eBay and try to get a whole lower unit with a 2.15:1 gear ratio, replace it in the outdrive, then sell the one you have now.

<font color=""ff0000"">I quess the other option is to rebuild or replace the head on the 170 and see how much longer the lower end holds together.</font> It seems to me that, in principle, it could be your cheapest option. However, the amount of blow-by gases coming from the crankcase is an indication that either the pistons need to be re-ringed, or the cylinders rebored and oversized pistons installed."
 
"I second El's last statem

"I second El's last statement. I have owned and worked on many, many 130/170's and this is by far the most common problem, wore out rings."
 
"Hey guys, Thanks for the info

"Hey guys, Thanks for the info. Could the blow- by gasses be coming from valve guides not rings? On this motor there is no block mounted breather vent. There is a hole for one, but it is filled with a cap/plug which appears to be OEM. If the ring blow-by gasses go up to the valve cover rubber elbow vent through internal passages is there any way to differentiate ring blow-by gasses VS valve stem/guide gasses? also, any rough guesses as to how much it will cost to have someone rebuild the head if I pull it and deliver it to a shop myself? I am thinking of doing the head first and seeing how things work out with cyl #3 back in the power cycle. Thoughts ??

Thanks again! Matt"
 
"If the valve stems were that

"If the valve stems were that bad the oil leaking thru would seal the gasses and you would leave a blue plume wherever you went from the oil being burned. Do a leakdown test and you'll find your problem although you already know your biggest problem, rings and or pistons."
 
"Boat Doc, Thanks for the repl

"Boat Doc, Thanks for the reply. I hope I am not missing something important here. I am under the impression that my biggest problem with this motor is that there is essentialy no compression on number 3 cyl. Yes, the rings are worn on all cyl's but w/o compression on #3 cyl I am only running on 5 cyl.s I believe the lack of "good" compression on #3 (at least as "good" as on the other 5) is a valve problem. The compression test I did showed that #3 cyl gained 20 PSI. when tested wet ( three good squirts of motor oil into spark plug hole) It went from 40 Psi dry to 60 Psi wet while the others cyls all gained 20 -25 Psi when tested wet v.s dry. However #3 never got above 60 PSI. Oiling the rings in #3 had the same effect as oiling the rings in all the other cyl's ...a 20-25 psi gain. This makes me think that the rings in #3 are as good (or bad) as the rings in the other 5 cyl's and that the lack of compression in #3 is a valve problem. Am I missing something here? I guess I will find out because I just bought a completely rebuilt head... new valve guides, new seats w/3 angle job, magnafluxed -no cracks or repairs. I hope this gets #3 cyl back in the power cycle. I really cannot afford to pull the whole motor apart now to do the rings and I think I can live with the blowby and reduced power due to worn rings. I do have a question about the distributor on my motor. My motor has a 170 label on the air intake box, has the 3 Solex down draft carbs and looks like a 170 to me. However, the distributor has a vaccum advance diaphram canister in it like I have seen in photo's of an AQ 165. There is no hose connected to the diaphram and I cannot see any place on the intake to hook up a hose to. Is this normal for a 170 to have the vaccum advance canister but no hose to it?
Thanks for the help and advice!

Matt"
 
"Before you do any work I woul

"Before you do any work I would narrow down the list of potential problems. Always start with a check of your valve clearance and look at your cam shaft lobes. When valves don't close or don't open correctly this can cause your compression readings to drop. After this is done, you should perform what is known as a differential compression test. It allows air pressure to be fed into the cylinder when it is at TDC allowing you to isolate the origin of the leak. If the leak is from your valves, as you assume, you will observe air leaking from the carburetor or the exhaust manifold. Otherwise it will be coming from the block as ring blow-by. Pistons are EXTREAMLY EXPENSIVE these days so I wouldn't go for the block rebuild without calling the bank for a loan. You can still get rings for about $50 for each piston. If I were you and if the problem is with the rings, pull that one piston while you are replacing the head and if you can remove the rings without damaging the piston, replace only them and ridge ream and hone out that one cylinder. Leave all other cylinders alone! You should be able to get several more good years out of it. Good Luck"
 
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