Evinrude 35Hp Question to John from Illinois

[G DANE]

I am going to rebuild an old engine i have lying this winther. I have a lot of parts from an old Evin 35 hp 1976 with damaged powerhead and a perfect 25 hp 1984 except from a broken gear. I would like to mix the two of them to a 35. I heard the powerhead is the same, except from airintake, reeds and carbureator. Is this correct? Is the cylinderhead the same. Is it possible to identify old evinrude parts by P/N on a website or elsewhere ?

 

[jegervais]

Re: Evinrude 35Hp Question to John from Illinois

I took a very quick glance at the 2 parts catalogs and they appear similar. I would suggest building your project on the 35 hp midsection. I do not know of any on-line parts catalogs, but if you're in no big hurry, let me know what specific parts you're looking at swapping and I'll see what I can come up with.<br /><br />-John

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Thanks John<br /><br />I have to use the 25 Hp midsection, as the 35 block and cranck are damaged. A dealer once told med that the 5 hp increase comes from better exhaust in leg, and the other 5 hp from carb, reeds and intake manifold. But he wasnt perfectly sure.<br /><br />The 25 Hp is a 84, and i think it should be propmesured, then.

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Swapping parts - i rebuilt the 35 hp i used to now, 2 years ago, using a RPM block with my used cranckshaft. At the end of season i had some problems which seems to be a bad sparkplug - i will know when i get the boat into water. I took a compression test, cold. I discovered the cylinderhead on the RPM block had a different shape with bigger wolume which gives lower compression. The 35 Hp RPM has 125, the 25Hp 133, same on both cyls. This leads me to a question ? Did a get a wrong cylinderhead with the Rebuild Powerhead ? Head P/N on rebuild 35 HP:323585 Roundshaped combustionchambers, im afraid it could be from a 20HP, maybe swapped at rebuild MFG ?? P/N on Blown Head, 35 HP from 1976: 319407, Sharpedged chambers.<br />P/N on 25HP 324319. Do i have the right cylinderhead on my rebuild 35HP ?

 

[jegervais]

Re: Evinrude 35Hp Question to John from Illinois

Cylinder heads: <br /><br />p/n 323585 is for 1978 20/25 hp motors. <br />p/n 319407 is correct for 1976 35 hp motors. <br />p/n 327671 is for 1984 25 hp motors. <br />p/n 324319 is for 25/35hp (I think) commercial motors, I cannot determine what year. <br />Sounds like you want to use the p/n 319407 cylinder head.<br /><br />-John

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Thanks again - You been a great help !!<br /><br />Dane

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

One More question, perhaps difficult to answer, but a can hear you have the experience, im only a kitchen mechanic.<br /><br />The compression on this motor with the 20/25 Head is 125 on both, new block, one new piston and rings on both. The compression on my 25 HP with correct head is 133 on both. Cold - no oil or anything. The correct cylinderhead had smaller combustion chamber, 10% less volume. Will the increase i will get in compression improve performance ?? Before i change the head - headgaskets are 65 USD here in Denmark !! Thanks for all your help, i really appreciate it.

 

[jegervais]

Re: Evinrude 35Hp Question to John from Illinois

Funny you should ask this question! I've been working on a project to boost the power output from a 25 hp Johnson. An increase in compression (by milling the cylinder head) did increase output. I don't know exactly how much because I wasn't using a dynomometer, but the engine was able to spin a test prop about 700 rpm faster, over the "stock" configuration. <br /><br />I can't predict the results you will have, but I believe you would see an increase.<br /><br />$65 USD!!!!! WOW!!!! They're only about $20 USD here...<br /><br />-John

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Thanks again John.<br /><br />I will try to get a gasket mailed from one of the companies in US, it is still much cheaper, weight is limited at all. I think 700 RMP means about 5 HP, which explains why i am not goung faster now, compared to my old 25Hp from 74. If i increase compression and RPM, i will probably get even more than 5HP, as the other differences in exhaust tuning in leg and bigger intake manifold should give bigger benefit when compression and RPM increases.<br /><br />Thanks !

 

[jegervais]

Re: Evinrude 35Hp Question to John from Illinois

I should probably clarify the 700 rpm's... The engine had "boggy" acceleration, so I fattened up the intermediate jet, this cleared up the acceleration problem, but the engine still wouldn't turn the recommended rpm on the test prop. I also fattened up the main jet (.004") this gained me about 350/400 rpm - the remaining rpm came from the compression increase. I haven't looked at the intake, reeds, reed stops or swapping carbs (yet)...<br /><br />-John

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

I understand this - but i have the correct carb and intake manifold. I guess jets in carb should be O.K. You just helped me find out that i was given the wrong cylinderhead.<br /><br />Its funny, i experienced a little sputtering too, with the 20HP cyl.head on, right after accelerating from iddle - at just above 1200-1500 rpm, then it dissappears. It is worst when engine is cold. I cleaned and cleaned carb, but same problem. It runs fine at all other rpm.

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

By the way:<br /><br />As far as i can see, reeds and reed plate are the same, guides may allow larger opening at WOT on 35HP ( bend longer back ). Intake plate is higher, letting more air in on 35HP. Carbureator is different too.<br /><br />Can you see what the correct main jet on 35HP should bee ?<br /><br />I know from experince this model must never run over 5800 RPM. The RPM powerhead i bought was from an OMC Dealer. He sold it to a State Scool. The students put the motor on an inflateable boat, without changing propeller. After only 6 HRS the Cranckshaft broke just below flywheel at WOT. It removed every conponent from ignition and almost got out through hood !!

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Bump !!<br /><br />Does anyone know the jet size ??<br />

 

[jegervais]

Re: Evinrude 35Hp Question to John from Illinois

Sorry I missed your earlier post ... The original jet was a #59D (.059") - I would suggest going up to a #61D (.061") for your rebuild.<br /><br />-John

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Thanks for all your help, i will change the jet.<br /><br />Im almost finished this repair - only waiting for a headgasket, i ordered online.<br /><br />I tried to put the 35HP cylinderhead on without gasket, to try - there was no clearence between pistons and head - crancking the motor, the pistons touched the head. I put the old gasket between and the pistons passes now. But will they still when rpms get high ? I was told pistons are the same on 20 - 25 - 30 - 35HP. Does anybody know ??

 

[jegervais]

Re: Evinrude 35Hp Question to John from Illinois

The best I can tell is that they are the same. I reviewed several microfiche from 1977 thru 1987, the newer the motors became, the more commonality there is between parts.<br /><br />-John

 

[G DANE]

Re: Evinrude 35Hp Question to John from Illinois

Thanks for your help John i really appreciate it !!