1954 25 hp Johnson RD-16 compression release?

[Motor Boater Bill]

I just got a 1954 RD-16 25 hp Johnson, and I know nothing about it's history, so I'm starting from scratch. No idea how long it has been sitting, but it is not frozen, the LU shifts properly, so far so good. Turning it by hand, the lower cylinder has obvious compression, but the upper has almost none. As I turn the flywheel, I hear the air excape as the cylinder rises. I have not measured the compression yet but the problem is obvious. Somewhere I seem to have seen a reference to compression release on some Big Twins, so before I tear into this I thought I should ask--did this model have compression release? If so, how can I check it out? And if there is no compression release, what's my next step in investigating this?

 

[OBJ]

Re: 1954 25 hp Johnson RD-16 compression release?

Look on the head for two springs and a flat lever that runs from the top of the flywheel down to the springs Bill. The lever is actuated by a maze on the flywheel to open the valves a little during pull starting.<br /><br />Not sure if your model has them or not....still at home with no shop manuals.....

 

[BoatBuoy]

Re: 1954 25 hp Johnson RD-16 compression release?

1956 RJE-18 30hp doesn't have decompressors so I'd be quite surprised if yours does. Below is a cross-section of a later model that does have them. <br /><br />My next step would be to get a compression guage and check the actual compression. If results were unsatisfactory, I would remove the head and see if gasket is blown.<br /><br />

 

[OBJ]

Re: 1954 25 hp Johnson RD-16 compression release?

Yep...what BB said....just got done looking at it myself....... The RD-16 doesn't have the compression release.

 

[Motor Boater Bill]

Re: 1954 25 hp Johnson RD-16 compression release?

Yes, there is nothing like that on my motor. Apparently it has the less-well-documented automatic internal compression release--also known as bad rings, blown head gasket, or other problems. I'm going to try some solvents before I pull anything apart to see if the rings are just crudded up. I can hear what I think is air moving internally when I turn the flywheel, so I think this would not be a blown head gasket unless there are internal passages (water?) that it could be leaking into. It doesn't seem to be leaking to the outside that I can tell from cursory observation. If it were leaking between the two cylinders it would affect them both instead of just one. Right?

 

[Chinewalker]

Re: 1954 25 hp Johnson RD-16 compression release?

Hi Bill,<br /> It could be leaking into the waterjacket through a blown head gasket. I would pull the head and take a look. Won't hurt anything to do that and will give you a better idea of what you're up against. Might also want to pull the intake covers and check the condition of the piston skirts and whether or not the rings are free or stuck....<br /> FYI - the 35s were the only ones to use the compression release system, c. 1957 - 1959.<br />- Scott

 

[surlyjoe]

Re: 1954 25 hp Johnson RD-16 compression release?

my 1960 Lark 40 horse has them..

 

[joaklay]

Re: 1954 25 hp Johnson RD-16 compression release?

I have two 25 HP Johnsons, a '54 and '55 and it takes only minutes to remove that head. Badly scored cylinder walls is NOT uncommon and if so, unless you really want to rebuild it, you can often find those powerheads on Ebay for cheap, ~$60 in good condition.

 

[Motor Boater Bill]

Re: 1954 25 hp Johnson RD-16 compression release?

Thank you one and all. I picked this motor up for a song as a project, so I'm into digging into it and seeing what I can find and learn along the way. I'll keep you posted.<br /><br />I also noticed that it seems to not want to tilt up--I noticed this when I went to tilt it up to spray some WD-40 into the cylinders. The latch that works with the shifter is released, so I think it is in the mounting assembly--but am I missing something?

 

[Motor Boater Bill]

Re: 1954 25 hp Johnson RD-16 compression release?

OK, I pulled the head. The head gasket seems OK but the cylinder walls are pretty deeply scored. I also found a piece of steel in the top cylinder, about 3/32 x 3/16 x 1/8. I'm thinking this is a piece of a broken ring, yes?<br /><br />I suppose the only answer here is a tear down and cylinder bore, oversize pistons and rings, right? Unless there is a simpler path--do they make just oversize rings? I think the scoring is probably too deep to just hone, but I'm outside of my experience here. Suggestions?<br /><br />Parting this puppy out may be the smart move!

 

[Paul Moir]

Re: 1954 25 hp Johnson RD-16 compression release?

Pistons and rings are (unfortunately) no longer available but they sometimes pop up from time to time, plus there's a number of places that stock NOS Johnny/Rude parts that may be able to help you out. Particulairly Stone&Sons marine & tcoutboards.com. Laing's outboard & vintageoutboard.com might be worth trying too. If you want to go that route.<br /><br />Joaklay's correct, good powerheads appear on ebay fairly often. I see one right now currently at $10, but the compression is unknown. Personally I would like to see a pic that showed the bores. Use these search terms:<br />(25, 25hp) (johnson, evinrude) (powerhead, "power head", block)

 

[tashasdaddy]

Re: 1954 25 hp Johnson RD-16 compression release?

my 55 15 hp has a latch on the front of the transom bracket, that locks the tilt latch. just a suggestion. does not operate with shift lever.

 

[Chinewalker]

Re: 1954 25 hp Johnson RD-16 compression release?

Bill,<br /> I've got a few parts blocks kicking around, and possibly a piston or two - all standard bore. Let me know if you need 'em...<br /> I'd never seen a 40 with the compression release - must have phased them out pretty early in the run, because the 40s I have seen have not had it....<br /> Thanks,<br />- Scott

 

[Motor Boater Bill]

Re: 1954 25 hp Johnson RD-16 compression release?

Again, thanks to all of you. What a great resource this board is.<br /><br />I won't be getting back into the shop for a few days. Meanwhile, a fishing buddy may be buying a boat with a 1950's 25 on it, so if he does I'll let him have this as a parts motor to keep that one going. Or--who knows--maybe I'll dive into it. Thanks for the info on parts.

 

[joaklay]

Re: 1954 25 hp Johnson RD-16 compression release?

Motor Boater Bill,<br />Just saw this today on Ebay. I asked the guy if he either knew its compression or had its cyl head off, "no and no" so there's no way to tell now as-is UNLESS you can convince him to remove its head for you. I've asked Ebay sellers to do that for me in the past and some will. He told me that his looks like its never been apart but that means nothing.<br /><br /> I doubt it'll sell for more than $50 but it might be better than what you've got: <br /><br /> http://cgi.ebay.com/ebaymotors/ws/e...d=1,1&item=4604963216&sspagename=STRK:MEWA:IT <br /><br /> Another thing to keep in mind with those early 25s is that they're almost worthless to most even in very good condition (which is rare, most are very rough). Those complete outboards often show up on Ebay too and rarely sell for more than $150 so whatever you do, don't spend too much money on parts for it.

 

[BoatBuoy]

Re: 1954 25 hp Johnson RD-16 compression release?

I may be out of line here, but that engine has a red (Holiday Bronze) head(1956 or later). I'd be apprehensive of any engine that's had the head replaced without explanation.

 

[Chinewalker]

Re: 1954 25 hp Johnson RD-16 compression release?

Good point BoatBuoy, especially since the '56 30hp head is quite different from a 25hp head... Domes are different shapes, with the 25s having a 5:1 compression ratio and the 30s having a 6:1 ratio. If the motor has not been pulled apart previously, then it still has the 25hp pistons in it, which would likely hit the head if using a '56 head. If they're not hitting the head, then someone has either cut the corners off the 25 pistons or taken a Dremel tool to the 30 head...<br />- Scott

 

[joaklay]

Re: 1954 25 hp Johnson RD-16 compression release?

I didn't look that closely before but you're right and yes, HIGHLY suspicious IMHO especially when the guy tells me that he thinks it's never been apart. There's also nothing that can go bad with one of those cyl heads so I'd have to wonder what happened to the original one?

 

[Motor Boater Bill]

Re: 1954 25 hp Johnson RD-16 compression release?

Is it possible that the block would have been bored to be fitted with the 30 hp pistons? Or to take that thinking a step further, since my motor would need to be bored to be usable, and oversize 25 hp pistons are not as readily available, would that be an avenue to conisder with my block?<br /><br />I agree with the comments above about not spending a lot on this motor. I'll also confess that my primary commitment as far as outboards go is to the 1976 20 hp Merc on my fishing boat, so this is definitely a second-priority project, and more about learning than a must-get-it-fixed-to-fish kind of thing. <br /><br />I reassembled last night it so I can set it aside for the time being while I determine what to do with it. Fitting the cowling/hood was a pain in the neck compared to "popping the top" on the later motors I've worked with. Particularly geting the screws through the sides lined up. Is there a trick to this, or just something they improved later?

 

[Chinewalker]

Re: 1954 25 hp Johnson RD-16 compression release?

Hi Bill,<br /> No boring is required to use 30hp pistons in a 25hp powerhead - they're the same bore. However, if you use 30hp pistons in a 25hp, you must use a 30hp cylinder head. <br /> It's rare to find NOS oversize pistons for your 25, whether you find 25 or 30hp pistons. They're out there, but they're not common and you'd have to hunt to find them. Buying the pistons and rings, and paying to have someone bore out the bores would probably result in spending a good deal more than the motor is worth, particularly since parts motors with serviceable powerheads are cheap and plentiful..<br /> I' m not saying don't get the powerhead on eBay, just don't spend much for it. It's possible it could have been rebuilt with the correct pistons, and rebuilt properly.<br /> Joakley -I've replaced cylinder heads on some motors when I've had a spare and the original had a stripped plug hole. .. It's not uncommon...<br />- Scott