15HP Powerhead - scored bores?

Hello, I'm asking for help with this as I'm at a crossroads.

This is my 15hp powerhead. I bought the engine as a non runner - the previous owner got it with a boat and didn't have any luck starting it. I'm assuming its the powerpack for now as there is no spark.

As it hadn't run for some time, and has comp. of around 75 on each cyl. pulled by hand, so I figured I would take off the head, replace gaskets and thermostat and re assemble.

What I found was as the pictures show - in some respects a very clean cyl. head with carbon build up on the piston crowns. The cyl. head looked undisturbed from new - the paint on the cable retainers was virtually intact when I started and the bolt heads were still covered in unbroken paint.

The water ways were quite clean, the thermostat corroded solid, but otherwise all OK I thought.

Looking a the bores, I saw some grooves - detectable with a fingernail, coming from the edge of the transfer ports on one cycl, and at the bottom of the other. I'm also still confused because the bores have no lip at all and stil have the criss cross diagonal honing marks all over them. The bore measures 2.182 with my vernier - not incredibly accurate I know.

So I'm wondering, is it a virtually unused motor?, is there ring trouble creating the scoring in the bores?, is the scoring responsible for poor compression (oil in the bores made no difference), have small parts chipping from the edge of the transfer ports gouged the bore? shall I just bolt it all up and see what happens, or pull it apart and see for sure? Is it just not run in yet? has it been carefully refurbished and just looks new?

If you can offer guidance on any of the above, please do! Its a 1978 model.

Thanks

Re: 15HP Powerhead - scored bores?

75 psig is good, especially for a hand cranked motor. I'd be inclined to put a new head gasket on and torque the head bolts, trouble shoot and try to run it.

While you have it open, you might check the bores for roundness, and measure the bores to know whether it's already been bored once or not.

Re: 15HP Powerhead - scored bores?

This is a Johnson ay? I recognize the thermostat housing. My 9.9 (basically the same motor, but different carb) had a compression of 110PSI in each cylinder, but was recognized as a rarity for it's age (1981). Comp testers vary amongst brands as well. I would agree with wilde, and say that there is little scoring at all in the cylinders, compression is even between both, I would slap on a head gasket and give her a whirl. You should be good to go man. If that were my motor, Id clean up the piston heads and be back into the assembly stage. Looks like if anything you had weak spark on the cylinder to the left and that is why it eventually would not start.

Re: 15HP Powerhead - scored bores?

no.
75 its too low.
i rebuilt this motor in the autumn.compresion i got 120.start first pull.

i would tear apatr powerhead,and rebore cylinders, instal oversize pistons.
or get new cylinder( the mechanist has one to handle), order new 2x set of rings+new seals and gasket set
its the best ways to fix this motor

Re: 15HP Powerhead - scored bores?

raczekp1 said:

no.
75 its too low.
i rebuilt this motor in the autumn.compresion i got 120.start first pull.

i would tear apatr powerhead,and rebore cylinders, instal oversize pistons.
or get new cylinder( the mechanist has one to handle), order new 2x set of rings+new seals and gasket set
its the best ways to fix this motor

Click to expand...

Well I do have 110 in each cylinder, so I dont totally disagree. But he should at least make sure he has used a reliable compression tester before breaking it down. I probably would have done a leakdown test as well. Just seems to me that if both cylinders are within 10% of each other it is worth looking into before a full rebuild.

Re: 15HP Powerhead - scored bores?

Hi fellas,
Thanks for the input. I'm a bit confused about the fact I can still see so much honing on the bores - thinking its either just been rebored or re honed for some reason, and I'm thinking/ hoping maybe its low 'cause its not broken in yet (too optimistic?)

Parts in the UK are not so plentifull or cheap as they are in the US, oversized pistons shipped from the US will cost me close to $160 in addition to the other service and gasket items running to around $100, making this an expensive proposition - not one I'd want to get wrong haha.

It's questionable if its economical to rebore and fit oversized pistons in this age of engine in the UK unless its an old and trusted motor. If I need a new powerpack as well after this it will be have cost more than the boat!

I confess i thought 75 psi was borderline, but hoped the figures might come up after it fired up and ran with sea foam for a while. I don't know if theres any reason to mistrust the guage, I've used it on other engines and had no reason to question the settings.

I guess the sensible thing to do is to strip the block and make sure the pins and rings are good, gap the rings in the bores and rebuild it all carefully with new gaskets. If it needs a rebore I think it might just have to go for spares.

Perhaps I'll just keep dismantling untill I know for sure.

Re: 15HP Powerhead - scored bores?

If the motor is fresh and not broken in, it would not have those slight cylinder scores. Honestly you may have had some type of gasket issue because the cylinders dont look bad to me. I have seen much worse with about the same compression that you are getting. If it were my motor Id put in a new thermo, headgasket, powerpack and fire it up. If it doesnt run, then you know that you have yourself a parts motor. No reason to break it down further if you already know that you arent going to rebuild it..... I will not fix something if it isnt broken. Plus you can part that thing out and get more than enough to buy a running motor if it is in poor condition.

Re: 15HP Powerhead - scored bores?

Thanks Sutor,
yes thats a logical way of looking at it.
The only consolation is that if I send off to ********** for parts I can always get my money back - so much cheaper than in the UK - just hovering before taking the plunge.

Re: 15HP Powerhead - scored bores?

ditto to sutor.......put it back together, see what happens. ( what year is it?, i might have a powerpack, shipping could be an issue tho)

Re: 15HP Powerhead - scored bores?

Hi, its a '78 motor, CD2 powerpack, thanks for even suggesting the powerpack idea - I might be able to borrow one here which can be guaranteed to work before I have to buy a new one.

Sounds like I better get the plastic out and make an order (thanks for the editing on previous post admin person, won't do it again!)

Thanks all for your wisdom.

Re: 15HP Powerhead - scored bores?

more than likely what your seeing is carbon scoring (minimal) carbon gets caught between the piston and cylinder at the top of the piston,check side ti side movement when piston is at TDC and then lower it down a bit and check it again, also check the top of the cylinder to see if it has a wear lip use your fingernail run it up to the top of the cylinder, if you dont feel a lip and side to side movement isnt bad i would decarbon piston/cylinder head and go with it

Re: 15HP Powerhead - scored bores?

I agree, that engine was run with crappy dinosaur oil (petroleum based) and probably has carboned up the second ring, and resulted in some blow by and loss of compression, hence the minor scoring due the the scuffing. Some of this occurs if you have a head gasket leak and water gets into the bores, washing them clean on oil. Either way, it is not severe enough to warrant a tear down and overhaul if you are on a budget. I would surface the head, clean up the sealing surface in it where the thermostat seal goes, replace the thermostat, seal, cover gasket and head gasket after removing the carbon from the head and piston crowns. Then I would run it until hot and take out the plugs, put on piston at the top and spray in some marime motor decarb solution through the spark plug hole until the combustion chamber is full. Let soak for 15 minutes with the cylinder as vertical as possible. Repeat for the other cylinder and then go run the engine for at least 1/2 hour to clear the stuff out. Then try your compression readings again. You may have to do several treatments to fully disslodge all the carbon in the ring grooves, be patient. Below is a 15 block that had the carbon cleaned off as described above and was returned to service..it only had 80 PSI before I did the de-carb solution, now it's back up to 115.

Re: 15HP Powerhead - scored bores?

why not to put apart powehead, do the honing job, instal new seals, gaskets and get new 2xset of rings.
i think honing job is low price, new rings is 30$ and gaskets also low price
all of job you can do yourself

Re: 15HP Powerhead - scored bores?

Sailpower said:

Hi, its a '78 motor, CD2 powerpack, thanks for even suggesting the powerpack idea - I might be able to borrow one here which can be guaranteed to work before I have to buy a new one.

Sounds like I better get the plastic out and make an order (thanks for the editing on previous post admin person, won't do it again!)

Thanks all for your wisdom.

Click to expand...

my "motor in a box" is an early 90's 15, that ignition wont work for you.

Re: 15HP Powerhead - scored bores?

Thanks, for the suggestion anyway.

I'm going to make the order and will probably be able to report back with some positive news in a week or two when they arrive. In the meantime I'll get everything else ready, including the conversion to short shaft. Thanks again to all.

To raczekp1, thanks , my inclination is the same as yours, to get to the root of the probelm, but since I'm doing this on a budget, I'll try the simple route first - worst case is I have to use a second set of gaskets of it doesn't improve. Thanks all the same!