Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

[joaklay]

I have a restored '57 18HP Johnson where the seller who restored it says that he used a newer 25HP powerhead but at one point wasn't sure if it was perhaps a 20HP powerhead (the original 18HP powerhead had a bent crank so he replaced the complete unit). Thinks is a '69-'70 vintage unit.<br /> Can I know the exact HP rating by an engine # stamped on the block? I have several old Johnson repair manuals but they don't specify HP ratings by any #s stamped on the powerhead unit itself.

 

[moderator1]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Moving to Johnson/Evinrude questions.<br /><br />I believe you will get a better response there.

 

[Solittle]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

I don't know your motor but many OMC motors have the model number stamped on a freeze plug that is on the block. They are round and slightly domed shaped. If you have one post the number here.

 

[joaklay]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Found it, the # on the casting plug is:<br /> <br /> 1722161<br /><br />...BUT, from what I've found listed in the link below, THAT # may not be usefull. It's not a model # but maybe a serial #?<br /> http://www.marineengine.com/manuals/johnson/#j20hp

 

[joaklay]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

So..............nothing? <br /><br /> Any other ideas?

 

[Chinewalker]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Hi Joakley,<br /> A few things to look for...<br /> Your serial number comes in as a late 1950s Johnson serial number. What color is (was) the motor block?<br /> I'm pretty sure the only real difference between the whole series of 22-cube OMCs (post 1968 redesign) was variances in the reed-stop height and minor porting differences. If your motor is indeed "restored" with the later powerhead, then it likely has the original 18hp carb and manifold which would in effect make your motor all of 18hp. The original 1958 18hp had a silencer over the carb intake, whereas the 1970-ish ones didn't. The later carbs were substantially larger and the old silencer wouldn't fit on them, and neither would the later carb fit on the earlier intake manifold.<br /> Also, does the cylinder head have a thermostat sticking above the top head bolts? They didn't add a t-stat until 1959. A 1958 cylinder head would not fit a 1959 or later motor block, and the '58 head would be required to allow a '58 hood to correctly attach.<br />- Scott

 

[joaklay]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Maybe the plot thickens?<br /> <br /> The engine was repainted as was the rest of the complete outboard so it all looks like new. <br />The guy who I bought it from (who's apparently in the marine business and restores these things often) claims that he used a newer complete 25HP powerhead (engine assembly), intake and carb off that motor (mine has NO silencer and I've seen pics of those too). It's also converted to a single fuel line, not the usual dual hose from that era.<br /> I have a vintage Johnson cd-rom that gives info to '64 and they didn't make a 25HP outboard between '56-'64. I have a '54 25HP Johnson too and it's a much larger engine by comparison.<br /> In the late 60s, early 70s, Johnson made both 20 and 25HP outboards where the powerhead assemblies look exactly like the late 50s 18HP to the naked eye (have pics of both to compare).<br /> I'd like to think that the sellers story is correct but then there must be a way to know which powerhead (for sure) mine really has.<br /> If the casting plug # above IS really a late 50s #, then I'd have to assume that the engine is really STILL an 18HP and that the seller made up the story about replacing it with a more powerfull unit but I don't know why he'd do that.<br /> The guy has a good reputation and I've bought other restored vintage outboards from him too.

 

[G DANE]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Hi joaklay<br /><br />On the early 70's 20/25, the powerheads had following:<br /><br />A 3 bolt thermostat cover on top of the cylinderhead, as Scott mentions. The leaf plate assembly has a small uncovered section, I think it is on starboard side of motor, ( left when seen from carb ) This small lip is uncovered by crankcase and intake manifold. The horsepower #20 or #25 is stamped in reed plate there. If you could advise the part number cast in cylinderhead og intake, maybee I would be able to find on to verify.

 

[joaklay]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Correction, my motor DOES have the silencer attached to the carb (carb looks very clean, rebuilt).<br /> There is NO t-stat. I'm unable to locate the reed plates, even with help from a manual here but on the starboard side there are two "bypass plates" near the newer fuel pump that both have the same #s 304781<br /> I don't see any other #s anywhere.<br /> The engine has white paint where the red doesn't cover it but that could be primer.<br /> I'd have to assume that I have an 18 HP engine, prior to '59.

 

[G DANE]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

The carb is bolted to the intake manifold. The reed plate is between this intake manifold and the block.

 

[joaklay]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

Possible to see #s w/o removing the intake manifold? All I can see is the outer edge of the reed plate with the manifold bolted to it.<br /> Would the '57 18HP motor also be stamped their too?<br /><br /> I do see a # on the intake manifold, that's 203907<br /><br /> From what's posted here by all who've helped out, it seems to be an 18HP motor from that year and perhaps original so I'm still baffled why the seller added (and insisted) that he replaced the unit with a newer, more powerfull unit. To me, the "restored" motor has more value as an original 18HP motor than if modified and the claimed extra horses isn't an issue, but I'd like to know what I have.

 

[G DANE]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

If you have the 22 cid motor 70-74 you will be able to see the 20 or 25 stamp without disassembling anything. Possibility is you have another 20 or 25 HP - older ?

 

[joaklay]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

The sellers ad said that it was a 25HP powerhead. Before buying it, I questioned him many times about that as it seemed unlikely to me that a 25HP powerhead would fit under the original '57 18HP hood and also bolt up to the original lower unit but he insisted that the later 60s-early 70s 25HP powerheads were physically the same on the outside as the older 18HPs were, said that you couldn't see the difference.<br /> At one point, he thought that (from his research) it might be a 20HP unit but wasn't sure.<br /> I'd think that the #s would clarify this? The fact that there's no t-stat (and never was one) makes me doubt the whole story IF it's true that "all OMC outboards have t-stats after '59".<br /> Is it possible that some newer OMC outboards after '59 didn't have t-stats? I'd think that logically once an idea was put into use, they'ld all be treated equally after that.

 

[G DANE]

Re: Johnson powerhead #s ('70ish), any way to know HP, 20 vs 25?

I never worked on motors older than start of 70 ies. If you go to his site: http://mitglied.lycos.de/old_omc/ you can browse old catalogues, as far as i remember there were made no 20 or 25 before start of 70 ies. Enjoy the site !