OMC 9.5 HP Power head

[Evinrude 25]

I have 1970 9.5 hp with 60/61 psi of compression and it starts and run. As per internet research, this 9.5 hp does not have high compression. Someone says 60-70 psi is a typical compression expected for it. Here is the deal, I could get a 1965 9.5 hp powerhead with 88/88 psi compression to swap over my motor. Base on reading, there are two groups of 9.5 hp, from 1964-1967 then from 1968-1973. Could anyone tell me that I could swap 1965 head to 1970? Is the block different between both groups or just internal components.  Does  (1968-1973) have more improvement over the previous years?

[Evinrude 25]

What is the compression number of 9.5 hp at new?

[crosbyman]

60-70 is fine  just enjoy it and don’t fix it if it works.  These are   casting/trolling motors and  great for float planes  transport

I have  refurbished 4-5 and they all had low compression but worked fine.   Run  some engine cleaner or some decarb product  if you want.

the earlier  pre-66   version  have  no vibration dampners    and known to shake a lot and pull out the choke !!! and die

some have  been known to choke on their own exhaust….  leaked up into the carbs  because the lower rubber skirt lets  lets fumes come  back up under  the cowl !!!

 

They are not  f-16…. mine  purs all day long

see Leroy’s  fine articles

http://www.leeroysramblings.com/OMC_9.5.htm

http://www.leeroysramblings.com/johnson_magneto.htm

 

Joining AOMCI has priviledges 🙂

1 user thanked author for this post.

Evinrude 25

[fleetwin]

Keep in mind that your compression gage might not be accurate as well.  And, I don’t know that I would trust someone’s claim that the older powerhead had higher compression.  Is your powerhead discolored, does it look like it may have been overheated?  If not, I would use it and enjoy it, perhaps run some engine tuner through it.  If you are still concerned, I would pull the cylinder head and have a look inside.

[Evinrude 25]

Hello Fleetwin,

My company has a good accurate pneumatic gage (I think +/- 0.05 psi). I have verified my compression gage against this gage to be sure my compression gage to be accurate as well. My power head does not show a overheat since there is no discolored on the head and the block. But the head is different color from the block so the previous owner had changed the head! I am very tempting to get this block on the Ebay since it has an impressive 105 psi. Wow it looks like very good compression for 9.5 Hp.  It is $75 but the shipping is a killer ($74). I am in Canada and live near the border so I could buy and ship to my friend house in US and just come over on the weekend to pick up. If this power head has truly 105 Psi, should I just swap to mine and will have a good motor for long. What do you think?

Here is the e-bay link

https://www.ebay.com/itm/325504635078?hash=item4bc99690c6:g:l6AAAOSwa6RjyK5W&amdata=enc%3AAQAHAAAA0Cmr51nnRsjNAetQExDjvpYoWVUgO6s2GGuJfy%2B22ChPDLj7eoS4%2BLWE3dSAcLLExAwfVL%2Bh38phw3s4paXw1e0MXt0bq4UY%2Fk6D5MDpneTKCMQAoGjMp9JcMIfCU8PFU7DVIowWhoDWXR86onbBlm92WaD6fHnVcbVRPXBEPkR9klNK8X0ocu7ydwWs48zP6ga6c7TfscRX2xaHEM2kKc%2FO%2FVPu7yzK68WL%2Bb6JyD9vCrt9DAkUuLxEMagaokTiyFeQvIH2ECRb3FshuM1VLaY%3D%7Ctkp%3ABk9SR4CNlvXdYQ

 

[fleetwin]

Evinrude 25 wrote:

Hello Fleetwin,

My company has a good accurate pneumatic gage (I think +/- 0.05 psi). I have verified my compression gage against this gage to be sure my compression gage to be accurate as well. My power head does not show a overheat since there is no discolored on the head and the block. But the head is different color from the block so the previous owner had changed the head! I am very tempting to get this block on the Ebay since it has an impressive 105 psi. Wow it looks like very good compression for 9.5 Hp.  It is $75 but the shipping is a killer ($74). I am in Canada and live near the border so I could buy and ship to my friend house in US and just come over on the weekend to pick up. If this power head has truly 105 Psi, should I just swap to mine and will have a good motor for long. What do you think?

Here is the e-bay link

https://www.ebay.com/itm/325504635078?hash=item4bc99690c6:g:l6AAAOSwa6RjyK5W&amdata=enc%3AAQAHAAAA0Cmr51nnRsjNAetQExDjvpYoWVUgO6s2GGuJfy%2B22ChPDLj7eoS4%2BLWE3dSAcLLExAwfVL%2Bh38phw3s4paXw1e0MXt0bq4UY%2Fk6D5MDpneTKCMQAoGjMp9JcMIfCU8PFU7DVIowWhoDWXR86onbBlm92WaD6fHnVcbVRPXBEPkR9klNK8X0ocu7ydwWs48zP6ga6c7TfscRX2xaHEM2kKc%2FO%2FVPu7yzK68WL%2Bb6JyD9vCrt9DAkUuLxEMagaokTiyFeQvIH2ECRb3FshuM1VLaY%3D%7Ctkp%3ABk9SR4CNlvXdYQ

 

Well, I believe your compression gage more than I believe the ebay ad’s claim of 105PSI!  OK, someone replaced your head, probably due to stripped plug threads.  Why don’t you go ahead and pull your head and have a look inside.  Clean everything up and replace the head gasket,  maybe even repaint your head so it matches the original color of your engine.  Don’t be afraid to “rough up” the cylinder walls with some crocus cloth/light emery to get rid of the glaze.  I know this sounds crude, but we are not dealing with rocket engines here, you won’t harm anything, just clean up the cylinder walls with some WD40 afterwards to get rid of debris.  Be sure the cylinder head surface is flat as well.

That ebay powerhead is pretty expensive when you include the shipping, I’m sure it isn’t going anywhere too fast.  Changing your powerhead is a pain, you have to pull those lower pans off, which means that many little springs/shims/mounts are going to fall/fly off and hide.  I wouldn’t attack this job unless it is truly warranted.  OK, so your powerhead isn’t discolored from overheating, although the original head may have been discolored.  I suppose the rings could be stuck, or perhaps the walla scored/scuffed from a lack of/wrong oil used.  Again, it is best to pull your head and have a closer look if you are concerned.

[Evinrude 25]

Your suggestion sounds to be a right track for me now. I don’t expect it is a output engine and go fast,  I just need it to be reliable, easy to start and good trolling motor.

I like 9.5 hp since it is light to carry and could troll for the whole day! I will try your method this week end and post the compression result.

What it the torque value of head bolts if you know by chance so I don’t have to look up. Other problem is that I could not get the torque gun access to two bottom bolts.

 

 

[crosbyman]

I doubt that 105 psi head   would come with a return  at no charge for shipping agreement….if not truly 105 psi  with your accurate meter

your total would be close to 150$ plus exchange  so we are talking 200$ cdn …

imho way to much $$   but it is up to you .  and you would be faced with a ph  job… and  apparently  a real pain to take apart

I paid $50 for this badly stuck 9.5    9622a     … but it became a gem at less than 70 psi

be patient and shop around on craiglist kijiji etc… for  “working”  bargains… even better with bad coils.  🙂

give your motor a good run  & see how it performs … it won’T break down  with  TLC

 

buy  fishing tackle gear  with the money saved .

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[crosbyman]

torque chart 9.5hp

 

Joining AOMCI has priviledges 🙂

[Evinrude 25]

Your 9.5 hp very nice finishing job! If I get mine up to 68-70 psi. I will do a dress up paint job for mine.

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