Re: 1989 Merc Blackmax comperssion low
Like was mentioned before, you really need to pull that head and have a look. You can bore up to three holes without boring them all but if you have to bore one on stbd and one on port the cost will be the same to just bore them all.
If you need boring you need to find a shop that is equipped to bore and hone a blind hole and knows marine engines. Your local automotive machine shops rarely have the proper equipment but may tell you they can do it. Run away from these offers.
Maximum bore is .020 without re-cutting the reliefs at the bottom of the hole. If you need to go .030 over make sure to mention the reliefs.
If you don't have a marine machine shop nearby don't forget to figure in the cost of shipping the block, (both ways). Go over to
www.screamandfly.com. Post your need for block work and there will be several highly qualified shops offering up their services. They are all the best at what they do and you won't have to worry about the work being done right.
A full set of gaskets does not include head gaskets. 150.00 is around the norm for what you'll need. The engine is 20 years old you need to take advantage of the opportunity to change all the bearings except possibly the lower main. You also need to replace all the rod bolts when you change the rod bearings. You should also change the reeds, rebuild the carbs and upsize the main jets by .002 for todays fuels.
You'll have a minimum of a month of evening work to complete the job and as much time waiting for parts you'll find you need along the way.
If you add it all up, you'll be in it around 2,000.00 plus the labor that you can do yourself.
A remanufactured (not refurbished) powerhead at around 3000.00 is the easier way to get your engine back up and running. Like was said before, you'll never know root cause unless you tear the old one down. You could very well end up bolting back on the cause of the problem and experience the same thing. I'm the second one to tell you this so believe it.
Your best and most economical option is to take the money you'd be investing in fixing this 20 year old motor and make a down payment on a new 150 Pro Max or find a good used replacement and part this one out on eBay.. If you find this to make sense then upgrade your U.S. Boats towing insurance, run this motor until it finally dies and then replace it.
On the other hand, if you can't put together the cash all at once for a replacement and saving just never seems to work out then go ahead and rebuild it. Take all winter and it can be like spreading the payments out over time. Just don't get anxious and neglect things you need to pay attention to.
