My 1979 9.8 Project

[keithb7]

I started my second Merc project. This one is a 1979 9.8 that I paid about $60 USD for. (I’m in Canada, $100 CDN) The seller told me it had been sitting outside in all seasons un-protected, for about a year. I figured, for the price it would at least give me a good supply of spare parts.



The engine was not stuck. It turned over. Upon disassembly I found a very clean engine in decent condition. Someone looked after it at some point and ran quality oil. Very little carbon build up. I ordered up new rings, seals and bearings.

I degreased and pressure-washed everything. Aside from spider nests, dirt and pine needles the enclosure was also in quite good condition. Even the paper engine mounting gasket was dry and easily removed in 1 piece. I gave the removed gaskets to my wife. She cut new replacements with a laser cutter. She did a great job.



Today I put masking tape over the original decals and painted the assembly. I’m waiting for the two new crank seals to arrive then I can reassemble the engine.

 

[merc850]

Looks like a good motor, how's the spark - LU?

 

[keithb7]

I’ve not fired it yet. Engine is still apart. I’ll deal with spark if needed, once I can turn it again.

 

[keithb7]

Cleaning up my 1979 9.8 noticed an engine SN on the powerhead. Canadian build. Was it typical for the SN to end with the year of manufacture? As seen here, maybe 41st build of ‘79? Maybe not.


I’m only curious as I picked up spare 9.8 parts outboard. Someone may have put together a mix parts. The leg SN plate is ‘74. The powerhead SN reads 7104920, quite a different engine SN pattern than my ‘79.

Progress on the ‘79 powerhead rebuild continues. I’m still waiting for new crank seals to arrive. I noticed some of the reed valves are not firmly closed in their relaxed state. There are 8 reed petals used. 6 firmly close and two have a small gap showing. I’ll order a new set and replace them all while the crank is out. Its a deep dive to get back in there another time. My understanding is poor idling and gas spitting back out of the carb is a typical symptom of reed vales not fully closing.

 

[merc850]

Here's the truth about reed valves: if one or more are stuck open, broken or chipped that might cause carb firing.

 

[keithb7]

Thanks for that max clearance spec on the reeds. I’ll measure my gaps. Pretty sure its over 0.010”

 

[keithb7]

My local Mom & Pop shop had 2 full sets of brand new original Mercury reeds. Under about 3” of dust. The shop has been awesome with almost everything I need for these old Mercs, in stock. He’s says nobody can afford to pay him to rebuild them any more.

 

[keithb7]

With the weather improving weekly, I look forward to getting out and testing my Merc rebuilds. I’m curious about the HP rating at the prop and at the power head.

My 1991 8 HP 2 stroke is rated at the prop. My ‘79 9.8 is measured at the powerhead. I’ve yet to use either of these as I picked them up over the winter. Under the same operating conditions can I expect the 8 hp to perform similar to the 9.8? When I do get out on the water I will use a GPS to record speed. Until then I’m curious. Thx.