1977 mercury 850 thunderbolt question

[04whitetb]

i'm doing a compression test on my merc 850,i'm using a flexable tube compression test kit from autozone tool rental.i can only reach the 2 middle cyl's.the upper and lower cowls make it very difficult to reach the upper and lower cyl's.any advice or different guage to use instead of removeing the upper cowl? and what about the lower cyl? thanks.

 

[narvlebenoit]

Re: 1977 mercury 850 thunderbolt question

you need to stay on one forum .

 

[Chris1956]

Re: 1977 mercury 850 thunderbolt question

The top cowl comes off. There is a flip toggle in the front top of the motor. That will expose #1 plug. I use a regular push in gauge with a 90* elbow to get all of the cylinders.

#4 is a bit tricky. You you remove the 6 bolts on the cowling support and the 4 self-tapping phillips head screws from the bottom of the cowl that says 85HP, the bottom cowl may move a bit for you.

 

[04whitetb]

Re: 1977 mercury 850 thunderbolt question

thank you chris,very helpfill advice.

 

[Moody Blue]

Re: 1977 mercury 850 thunderbolt question

I took the lazy mans approach to this problem. I got tired of trying to access the lower plug, so after careful measurements, I cut a 1 1/4" hole in the lower cowling with a holesaw in-line with the lower plug. I have a rubber grommet that fits the hole perfectly and seals it up tight. Now I can get a plug socket or compression gauge in there with ease.

 

[Chris1956]

Re: 1977 mercury 850 thunderbolt question

Gee Moody, that is a radical solution. An open end 13/16 wrench easily removes the spark plug. A compression tester with a brass elbow allows access to test the compression of all cylinders.

Good thing you are not running for President. You are too radical...LOL

 

[Moody Blue]

Re: 1977 mercury 850 thunderbolt question

Yea, I have a tendency to come up with unconventional (yet effective) solutions to problems I encounter. Works for me though

 

[daveswaves]

Re: 1977 mercury 850 thunderbolt question

Yea, I have a tendency to come up with unconventional (yet effective) solutions to problems I encounter. Works for me though

Must be a Canadian thing, I am considering the same hole.

 

[merc850]

Re: 1977 mercury 850 thunderbolt question

I have a tester with the rubber hose so I bent the hose with one hand and held the brass threaded insert against the hole with the other, then turned the hose and it threaded the insert in. Have done this several times.

 

[Maxz695]

Re: 1977 mercury 850 thunderbolt question

A man gotta do what a man gotta do

 

[Moody Blue]

Re: 1977 mercury 850 thunderbolt question

Must be a Canadian thing, I am considering the same hole.

Highly recommended. No cursing or fussing anymore for me.