'91 Mercury XR4 - help with rebuild?

seo515

Cadet
Joined
Jul 6, 2010
Messages
13
Hi again, this is my second thread in regards to my outboard. After de-carbing my engine and still having too low of compression(85lbs while the others are 125-130) in my #2 cylinder, I have decided to try and fix the problem myself.

BRIEF HISTORY OF OUTBOARD: I bought it from a seller who "claimed it ran great. He bought it from his father-in-law after it had been sitting for several years. The seller admitted he knew nothing about boats and all he did was put oil in the injection and fuel in the tank and ran it several times. I brought it home and put it on the muffs. Immediately, I get a constant beeping sound and then a few minutes later, got the overheat buzzer. I turned off the engine and later replaced the entire water pump and both thermostats. Now it doesn't overheat, but the oil-injection system has an issue. I'm not too concerned with that right now since I mixed oil with the fuel for the time being. I'm guessing the damage to the #2 cylinder was a result of overheating from the lack of oil.

I have no real experience with working on outboard engines other than the basic maintenance stuff that anyone can do. I lost a lot of money from purchasing the boat and motor from a dishonest individual. I've invested too much money into the purchase of this lemon and can't afford to pay a mechanic over $1k to rebuild the bad cylinder. Based on the information I've found on this site, I think I will need a new piston(oversized), ring, head gasket, torque wrench, and have the cylinder honed/rebored/resleeved(not sure of these terms, but basically I'm assuming it needs to be reamed to allow the larger piston. Do I have to remove the entire powerhead or can I just remove the crankcase? Is this job something a person with average intelligence can do or do I need to have some mechanical background/knowledge to tackle such a project?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: '91 Mercury XR4 - help with rebuild?

Go to the link below and purchase service manual. Then read, read and reread before turning a bolt on this. The powerhead will need to be removed and torn down. The cylinder damge could be minor or major and that will decide if it can be honed or need to be bored. While its down its foolish not to go ahead and re-ring the other cylinders as they are 20 years old. If the oil gear went down its possible that the gear debris may have damaged that cylinder or maybe some more cylinders. If you need parts,support or advise you can pm me....

http://cgi.ebay.com/ebaymotors/1991-Mercury-Mariner-V-135-thru-V-200-Service-Manual-/120708319689
 

seo515

Cadet
Joined
Jul 6, 2010
Messages
13
Re: '91 Mercury XR4 - help with rebuild?

Fatzbullet, thank you for the link to the service manual. I bought a Seloc manual from eBay for V6 powerheads 1990 through 1994. I figured this was better than the other Seloc manual that covers all outboards in a 10 year range. But, I know they are not as good as the service manuals. But before I purchase the service manual, is it even realistic for someone with no experience in working on outboards to do a rebuild? Is there anything you recommend that I should check before attempting this? I thought about changing the head gaskets to see if there might be a leak. Do you think I should attempt this first? Will taking off the head cover and posting pictures of the cylinders and piston help in getting assistance with my problem?

I saw a rebuild kit on eBay for $780. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=260190750827
Is that a good deal or does it include too many unnecessary items that I don't need?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: '91 Mercury XR4 - help with rebuild?

Pull the heads and inspect cylinder walls. Grooves ,gouges and deep scuffs are not good. Yes you can fix it if you are some what a mechanic and have access to tools. Dont order anything till you get it apart and can inspect and mike cylinders and pistons...
 

seo515

Cadet
Joined
Jul 6, 2010
Messages
13
Re: '91 Mercury XR4 - help with rebuild?

Ok, today I removed the head and took a look inside. I took several pictures and have uploaded them below. It appears that the #2 cylinder wall is "scored"(not sure if that is the correct term). As for the piston, I don't know much about engines to know whether it's supposed to look like that or not. The compression on the #2 cylinder is 85lbs(went up 15lbs after de-carbing), while #4 and #6 are 130 and 125. The head cover shows a lot of carbon build up, especially in #4. #2 looks cleaner probably because I've been seafoaming the crap out of it. I did notice a small hole on the cover of #2 as shown in the picture. Is that something to be concerned about? I noticed a lot of dark oil inside the piston area, and some seeped out of #6. I guess that's because everything drains down into that cylinder? Is dark oil normal?

I sprayed more seafoam into the cylinders to help clean it some more. The head gasket cover had a lot of rust. Is that a potential symptom of another problem? I went ahead and replaced the gasket and put the cover back on. I hope that these pictures will help to get some advice/comments on the problem I'm having. I'm hoping to try anything and everything to avoid a rebuild. Thanks in advance!
 

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Sprky

Petty Officer 1st Class
Joined
Aug 7, 2011
Messages
277
Re: '91 Mercury XR4 - help with rebuild?

The proper fix is tear down, bore and oversize piston.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: '91 Mercury XR4 - help with rebuild?

The proper fix is tear down, bore and oversize piston.
A teardown and inspection and "miking" of all cylinders are needed. That cylinder will need bored and repacement piston but this is not a oil related failure...
I'm guessing the damage to the #2 cylinder was a result of overheating from the lack of oil.
Being most damage is on exhaust side of piston I would inspect the ignition system for a defect such as defective idle/spark advance box or bia's problem in switchboxes. If it where on intake side I would lean towards carb problembut you need to rebuild them anyway if you repair engine...
 
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