ad10 compression

popsmazz1 · Dec 2, 2007

what should the compression be on an a10 be, the one I freed up has 70 psi on both cyls, seems low to me.

HighTrim · Dec 2, 2007

Re: ad10 compression

All gauges are a bit different, what is truly important is that the cylinders are equal, although they seem a tad low. Could always try a decarb, bring the motor to operating temp , then try again.

F_R · Dec 3, 2007

Re: ad10 compression

70, if accurate, is low. Rings are probably stuck for the same reason the pistons were. If you can get it to run, they MAY free up with de-carb. However, I really don't approve of starting a motor that was frozen without being absolutely sure there is no rust in the crankcase/connecting rods. If there is, they will self-destruct.

popsmazz1 · Dec 3, 2007

Re: ad10 compression

do you think it will run with that compression? it needs new coils, is it worth putting any money in it?

F_R · Dec 3, 2007

Re: ad10 compression

Hard to say. Even if it does run, are you prepared to spend at least $100 on it? You will, by the time you buy ignition parts, carb kit, and water pump.....or more. Do you have a gas tank?

If you don't want to invest the money, perhaps it would be a good thing to place a free Webvertize classified ad over at aomci.org. Might get a few bucks for it, even if only for parts.

jbjennings · Dec 3, 2007

Re: ad10 compression

MY '53 10hp I ordered only had 65lbs. and it would run, and even idle, but wouldn't run wide open and made all kinds of racket. Sounded like a loose wrist pin or something. Basically a boat anchor. My '55 10hp. has 85 and 88 lbs. and runs great.
Good luck with yours,
JBJ

samo_ott · Dec 3, 2007

Re: ad10 compression

I agree, 70 is a tad low. 80 would be good... Decarb it and hopefully the rust will not be an issue!

wbeaton · Dec 4, 2007

Re: ad10 compression

I have seen them run as low as 60 psi. 70 is ok. I'm with FR, though. I wouldn't run it until I opened the block and checked/cleaned everything. I can tell you it costs about $150 CDN to tune one of these motors and closer to $200 if you have to reseal the lower unit as well. Unfortunately, that's about the value of the motor. Don't be afraid to open it up. There aren't any special seals or anything to replace.

popsmazz1 · Dec 4, 2007

Re: ad10 compression

believe it or not I found that my buddy when he took it apart 25 yrs. ago he put the head on upside down, now the comp. reads 75&80 psi. he also gave me the old 2 line gas tank that looks ok. I am going to put new coils in it and see if it will start. if it will I will put a water pump in it. I would like to keep this old motor I hate to see it end up as junk in some scrap yard.

jbjennings · Dec 4, 2007

Re: ad10 compression

I'd almost bet that new coils and clean carb and new impeller and you'll be in business. I LOVE my '55 10hp johnson! It's VERY smooth on idle and acceleration, nice and quiet, and starts easy as all Johnsons do. Post a pic of 'er running---I'd like to see it. Make sure you don't squirt anything but premix in the carb when you are first trying to start it so it'll get plenty of oil on your initial startup after such a long sit.
Good luck,
JBJ

popsmazz1 · Dec 5, 2007

Re: ad10 compression

going to give a shot in the spring, cant do much now its stinking winter, and the snow is flying.

ad10 compression

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