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  1. K

    1981 Mercury 7.5 2 stroke

    I spent some time researching the air coming out the end of the crankshaft. I studied the parts and technical book and a few other similar models. Nothing confirmed my inquiry. I sprayed soap in there and pressurized it to maybe see where the air was coming from. Inconclusive. I tried applying...
  2. K

    Motor Won't Turn Over

    The engine is turning over. The flywheel and crank are turning. Its not seized. “Won’t turn over” generally means the engine is seized. Your engine is not seized. It just wont stay running. I assume this is a fuel injected 4 stroke?
  3. K

    1981 Mercury 7.5 2 stroke

    I’ll take a closer look in there later this evening. Looking at the Mercury parts web site, they only show a felt washer in there. I do have that. Its in place. #4 in the image below. #2 is the lower crank seal. My engine does not utilize #3, some type of spline adaptor. Perhaps a little...
  4. K

    1981 Mercury 7.5 2 stroke

    Leaking air out center area here.
  5. K

    1981 Mercury 7.5 2 stroke

    Leak down test shows the new intake port inspection cover leaking. Tightened it again still leaks a small amount. I’ll remove the gasket and spray some Permatex Copper Gasket aerosol on both sides. Reinstall install it again. Minor issue but might as well do up right. Another interesting...
  6. K

    1981 Mercury 7.5 2 stroke

    MHeating from crank bearing housing worked perfectly. Thx. I completed powerhead reassembly yesterday. Today I’m sourcing some material to make the exhaust block-off plate. I’ll pressurize the assembly and monitor for possible leak down. I noticed less sprung piston ring movement when...
  7. K

    1981 Mercury 7.5 2 stroke

    I have a couple questions: The small holes in the tops of the pistons. Are they possible lube holes to piston pin? I’m doubtful but want to be sure. I can’t seem to spray aerosol lube down thru them. Next Q. What’s suggested method to get the upper main crank bearing out of the housing? A...
  8. K

    1981 Mercury 7.5 2 stroke

    @racerone earlier mentioned changing the upper water tube plastic washer. I was wondering where this was. Found it. Thank you!
  9. K

    1981 Mercury 7.5 2 stroke

    My local marine dealer had everything I needed stock. I’m impressed. Clean up time and reassembly next.
  10. K

    1981 Mercury 7.5 2 stroke

    I removed and tore down my 7.5 tonight. These things are so simple. Easy to work on. The whole experience was a pleasant. One of the easiest engines I’ve ever pulled and opened up. The cylinder walls look great. No scoring seen. Some mild scoring on the rings. The crank seals were pretty...
  11. K

    1981 Mercury 7.5 2 stroke

    The rings are sprung. I’m not convinced they are stuck. I see enough scoring on the rings to lead to low compression numbers. Ideally I’d like to get full power from this engine. It’ll be going on a 10 ½ foot SIB. It won’t be mainly trolling around fishing. This project is my first time digging...
  12. K

    1981 Mercury 7.5 2 stroke

  13. K

    1981 Mercury 7.5 2 stroke

    Reporting back. Removed bypass access cover. All rings are still sprung. None broken. I see fine scoring patterns on the rings. They look pretty worn to me. I’ve limited experience with this. I attempted to take a few photos. Difficult to get clarity with cell phone camera. Hone and ring time?
  14. K

    1981 Mercury 7.5 2 stroke

    Will do. Thx. Any chance that piston ring end gap would be measurable from that by pass cover? I suspect no, that end gap pins will be 90 from the ports. I will inspect rings and test them for spring tension.
  15. K

    1981 Mercury 7.5 2 stroke

    Sorry. Yes smaller ports on 7.5 compared to a 9.8. I did some internet searching. I found some posts where folks were claiming 100, another 165. https://forums.iboats.com/threads/compression-for-a-7-5-hp-mercury.236135/...
  16. K

    1981 Mercury 7.5 2 stroke

    My understanding is piston rings wear over time and compression slowly drops. There does not need to be any visual damage to piston or rings for compression to be low. Could just be a tired engine. Maybe 70 or 80 psi is all these 7.5 hp engines ever made. Looking to confirm. The 9.8 and the...
  17. K

    1981 Mercury 7.5 2 stroke

    The Mercury Shop Manual I ordered arrived. It covers the smaller Mercury outboards, including my 7.5 HP. I was hoping to find stock compression numbers. They don’t publish them in the book. Can anyone tell me what the compression should be on my ‘81 7.5 HP engine. I have measured my engine and...
  18. K

    Possible water intrusion or lean sneeze?

    Possibly related: When storing a two stroke; standing upright is ideal. If laying down, spark plugs are to be up. This keeps the cylinders higher than the prop. Residual water in the cooling passages can flow into the cylinders if stored incorrectly. While stored, this water will cause piston...
  19. K

    1981 Mercury 7.5 2 stroke

    Thanks. I will try those web sites. I have already pulled the lower leg measured, the shaft and ordered a water pump. Its on the way. The thermostat was removed. I also ordered one.
  20. K

    1981 Mercury 7.5 2 stroke

    I recently purchased a used 1981 7.5 hp outboard. I plan to use it with a small SIB. I am new to outboards but not new to mechanical repairs. I’ve rebuilt multiple other types of 2 and 4 stroke engines. I tend to source an OEM service manual ASAP. I’ve not found one yet but I will. Is anyone...
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