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1978 Aq120b

A

atoughram

New member
I recently purchased a boat with a AQ120B/270 Stern Drive (1978 Bayliner Mutiny). The motor wasnt running and the PO said that the teeth were stripped off of the timing belt. I purchased a timing belt and began to change it, when I found that the motor was frozen up. (I guess I should've tried turing it over first!). The spark plugs were removed by the PO's mechanic and never reinserted. The timing belt is indeed pretty wasted.

I've found several auto motors, both a B21 and a B230F that I can replace the AQ120B with. I've had several B230F's in cars, and know the basics of these engines, but I'm not sure which would be the best motor to replace the AQ with. It looks like I need to change the manifolds, distributor, alternator, and the camshaft. Is this correct? How about the intermediate shaft and timing cover?

Is it possible to retrofit the automotive electronic ignition onto these engines? Has anyone tried to fuel inject them?? I realize these are non-marine items but I'm curious.

Thanks!
 
Re: Aq120b

find you a b230 89 to 94 vintage,avoid 85 to 88 engines,these were low friction engines and the conn rods and bearings are smaller thus not as durable.you will have to use marine cam,you will have to use the intermediate shaft and cover off marine engine as well as dist,intake.as for fuel injection,you have to take into consideration that every piece of whatever you install(fuel pump,hose,etc)has to be USCG approved for marine use,yes it can be done but the cost is not justified.
 
Re: Aq120b

I found a 1990 B230F with less than 100K miles on it and the distributor is in the block! Looks like I'll be busy this weekend! Thanks for the help.
 
Re: Aq120b

The man was mistaken, the distributor is on the head, but I dont think that will be a problem, I'll just pull the plug on the block and put the marine distributor in there. Unfortunately it doesnt have a hole machined in the block for a mechanical fuel pump, so I will end up installing a electric fuel pump. Is the flame system (PCV) easily plugged? I called Delta Camshaft in Tacoma Washington http://www.deltacam.com/ , and they have the "A" profile and can grind my cam to that profile for a reasonable price, I'll just have to make the proper adjustments in the shims. Anything else I might've missed? What about rejetting the side draft carb for the 2.3l instead of 2.1l? Does anyone think it will run too lean?
 
Re: Aq120b

use your cam out of the original marine head,the V cam is the best,I have a good A cam, if it becomes an issue i will part with,you will have to swap the accessory shaft because the one in the auto block wont have drive gear for dist.most of these blocks have a blockoff plate for mechanical fuel pump,just take off and add mech pump,the crankcase breather is a dirrect swap-out.You shouldnt have to anything to carb except adjustments.
 
Re: Aq120b

I'll have to look at it again, but I dont think the hole for the fuel pump finger is even there, I dont think there is a block off plate. I figured I'd have to swap the accesory shaft, as the raw water pump is driven from the front of it.
 
Re: Aq120b

There is no hole for the fuel pump finger - I will have to put an electric pump on it, but thats not problem. I've almost completed the swap, almost everything bolted right into place but a few things. The snout on the automotive crank was different, so the marine pulley and crankshaft timing belt pulley would not fit, but the automotive version will work fine. The marine circulation pump would not fit on the automotive block either, I will end up using the automotive circulation pump and either finding a one piece Volvo Penta heat exchanger, or adapting a "Log" type heat exchanger onto the engine. The automotive intermeadiate shaft neither had the lobe for the fuel pump nor the gear for the distributor, but the marine shaft slid right in - after I dropped the pan, removed the oil pump, and pushed the gear up and out of the way. The intake and exhaust manifolds bolted right up without a hitch, but the automotive head had an AIR system on it, and has ports drilled into the exhaust ports that will have to be plugged up. The oil pressure sender on the marine engine looks like it's 1/8" NPT thread, but the automotive is some sort of straight thread with a crush washer, I'll have to find an adapter. I retained the oil sperator on the automotive flame trap system, and will route a breather tube into the flame arrestor instead of coming out of the valve cover like the marine engine. I had to remove the plug for the distributor to go in the block, but it appears that the distributor will fit right in. I left the the automotive distributor on the back of the head, it will just be a spinning shaft, I figured it wont hurt anything. I also ordered the wrong timing belt, since I had to use the automotive crankshaft timing belt pulley, I had to stick with the automotive cam and intermeadiate shaft pulley too. Some time between 1978 and 1990, they changed the timing belt tooth design from square to a round tooth, probably to quiet it down. I'll put the old belt back on for now.

More to come...
 
Re: Aq120b

I forgot to post how sea trials went! With the automotive cam still in the head, the new B230F motor must've had way more power than the old AQ121 motor did as it will over rev the engine with the same prop. The boat easily gets up on top of the water, and I was thrilled! I ended up finding a one piece heat exchanger and all the fittings off a junk motor so the cooling system is in good shape except for a couple of weeping o-rings. I've winterized it for now but when she wakes up in the spring, I'll need to change the exhaust manifold gaskets, some o-rings on the cooling system, and wire a safety switch into the electic fuel pump along with swapping in an electronic ignition into the exsisting distributor.
 
Re: Aq120b

Do note that the Marine Approved electric fuel pump must have the low oil pressure switch in the loop!
This is a USCG requirement!

This will be a N/O pressure switch that will kill electric power to the fuel pump, should oil pressure drop to 5-7 psi (I believe).

This also means that a "start by-pass" circuit will be required for start-up when/if fuel has evaporated from the carburetor.
Make sure that neither can back-feed the other.

.
 
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