Alright so I picked up a 1978 9.9 HP evinrude this past winter and when I checked it it had 100 PSI on the top cylinder and 97 on the bottom. Ran fine in a barrel. Took it out in april and it overheated, but didn't sieze up. Checked the combustion chambers and I didn't see any scoring. Rechecked the PSI it was 75 on both cylinders. Took it to a backyard mechanic since no regular mechanics in the area will work on anything older then 10 years old. He thinks 75 PSI is fine for this older motor but after getting a few second opinions I disagree. The motor runs fine in a barrel, but I don't think I'll get the horsepower I'm looking for out of it, which was why I bought it in the first place. He installed a new water pump, cleaned the carb and put a new kit in, and replaced the powerpack. He also found an issue with a rubber gromet somewhere along where the lower unit connects to the powerhead that was obstructing water flow. . . The thing starts but he thinks replacing the head gasket would be a waste of money. . . . The motor also didn't have a thermostat and he claims that I don't need it, but I've found information saying otherwise on leeroys ramblings. He thinks 75 PSI for the year is fine, and that since I've got equal PSI on both cylinders I'm fine. . . This guy is an old timer and has a lot more experience working on these motors then I do, I respect him so I didn't argue with him. He doesn't like to hear what other people say because he's the one doing the work so I can understand where he's coming from. . . . I really feel like he's cutting corners though with the thermostat and the compression issue. So I ended up paying him $240 for the work he did do, so I'll have to throw on a new head gasket myself and see what happens. . .
Alright, so I guess I'll check to see if the head needs to be resurfaced and throw on a new head gasket after that. I found some information online that says I need to remove the whole powerhead to resurface it. . . is that really the case? If so then this project isn't something I can handle then. . . The actual concept of resurfacing the head doesn't seem to bad though. I figure I can just use some grit wet sandpaper on top of a flat piece of glass. From what I've read I'm supposed to sand in a figure 8 motion until there are no gaps exceeding 0.003? Do I really need to check for warpage or can I just throw on the new head gasket and recheck the compression? What PSI should the bolts on the head be torqued too, and in what order do I do put the bolts back on? I think this is a job I might be able to handle if I don't have to actually take the whole powerhead off. . . .. The motor isn't seized and it still runs, there's no scoring in the combustion chambers. I haven't been able to take it out on the water though so I don't know what it's going to be like running under load, and what kind of speed I'm going to get out of the thing. . . Replacing the head gasket and checking to see if it needs to be resurfaced can't hurt though, I don't have a torque wrench though guess I'll just need to rent one. . . .
Here are some pictures of the what I'm looking at. . . I took the cylinder head off in late april right after the heating issue.
Alright, so I guess I'll check to see if the head needs to be resurfaced and throw on a new head gasket after that. I found some information online that says I need to remove the whole powerhead to resurface it. . . is that really the case? If so then this project isn't something I can handle then. . . The actual concept of resurfacing the head doesn't seem to bad though. I figure I can just use some grit wet sandpaper on top of a flat piece of glass. From what I've read I'm supposed to sand in a figure 8 motion until there are no gaps exceeding 0.003? Do I really need to check for warpage or can I just throw on the new head gasket and recheck the compression? What PSI should the bolts on the head be torqued too, and in what order do I do put the bolts back on? I think this is a job I might be able to handle if I don't have to actually take the whole powerhead off. . . .. The motor isn't seized and it still runs, there's no scoring in the combustion chambers. I haven't been able to take it out on the water though so I don't know what it's going to be like running under load, and what kind of speed I'm going to get out of the thing. . . Replacing the head gasket and checking to see if it needs to be resurfaced can't hurt though, I don't have a torque wrench though guess I'll just need to rent one. . . .
Here are some pictures of the what I'm looking at. . . I took the cylinder head off in late april right after the heating issue.
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