1986 175 HP black max v-6

[jigmister]

Had temprature fluctions. MAJOR from hot to super cold.

pulled the plugs and found water in star lower cylinder. sure enough head gasket blown.
inspected cylinder wall.
found MANY little tiny pits.
read manual and learned I have chrome cylinders????
As maunal recommened I swabed the pits with toilet bowl cleaner

I found no fizzing or bubbling to indicate the chrome is gone to aluim.

from what I can tell, the manual is telling me things should be ok??

I really dont have the funds for a new power head.
Am I going to be ok for a good while or will the new gasket only solve my problem for the short term.
I am concenred with the cylinder wall but just not sure how to determine if what I am finding is damage or not.
the book clearly says not to mistake porosity for a damaged cylinder.

What bothers me is I don't see pitting or "porosity" in the other 2 cylinders.
clearly the walls are smooth to the touch. in fact I can not really even feel then when I run my finger tips across them. Only one larger pit can I feel.

book goes on to say that if the chrome is gone a NEW block is needed.
I have to think there is another way to repair. such as a sleeve.

anyone have experince with this matter?
thank you for reading

Jim

 

[achris]

Re: 1986 175 HP black max v-6

Small pits are very common in chrome bores. You did the 'toilet bowl cleaner' test and that showed no ali.... From what I read in you post, you should be ok for a good few years yet. Are you sure it was the head gasket that was blown? The reason I ask is because the exhaust cover gaskets are usually the first to let water through. It's recommended that on an interval of about 5-7 years both exhaust cover gaskets and both head gaskets be replaced. They also recommend that the lower crankshaft seal be done too. I'm yet to see a leaky one. With the constant heating and cooling on either side of those exhaust gaskets they get brittle over time and start letting water passed. You see a slightly cleaned area on the sidewalls of the exhaust chamber when you pull the covers off. Don't forget to replace the silicone sealing strip between the banks either (if that model has it).

Good luck,

Chris..............

 

[jigmister]

Re: 1986 175 HP black max v-6

thatnks for the tips!

exhaust cover gasket?
hmmmmmmm.. I am certian that the head gasket was allowing the water in.
I was able to see where it had broken at the metal ring.

how hard is it to change the ex gaskets?

 

[achris]

Re: 1986 175 HP black max v-6

exhaust cover gasket?

how hard is it to change the ex gaskets?

Not hard at all. There are 2 covers. Makes sure you have gaskets for each and a new silicone sealing strip. Just remove anything hanging off the cover and then remove all the screws holding them on... About 38 from memory! (It feels that way whenever I have to remove one). You will probably find that some of them are tight. Don't try too hard, if it's tight, give it a firm strike with a drift and hammer. That may loosen it enough. If that doesn't work, then I usually pull out the red spanner. Heat the screw up nice and hot, red hot, let it cool and hit it with the hammer and drift again. The thing that usually makes the screw tight is damp corrosion product. Heating it dries it out and makes it like a white powder, just falls out once the screw's removed. Before you put the screws back, clean them with a wire brush on a bench grinder and the holes with compressed air. Put a bit of water proof grease on the screws and they'll torque up smoother and be easy to remove when you do the job next time. Use lots of grease to hold the silicone sealing strip on the block (between the 2 cylinder banks) as you put the inner cover on.

Cheers,

Chris...............

 

[jigmister]

Re: 1986 175 HP black max v-6

Use lots of grease to hold the silicone sealing strip on the block (between the 2 cylinder banks) as you put the inner cover


???

what is the sealing strip? is it a part I need to get or dose it get used again?

 

[achris]

Re: 1986 175 HP black max v-6

Use lots of grease to hold the silicone sealing strip on the block (between the 2 cylinder banks) as you put the inner cover


???

what is the sealing strip? is it a part I need to get or dose it get used again?

The seal is #3 on the diagram. It's part number is -69668. I replace them every time. And there are 21 bolts holding the covers on.

 

[jigmister]

Re: 1986 175 HP black max v-6



thank you for all the help.

 

[jigmister]

Re: 1986 175 HP black max v-6

I got it back on the water today.
now my concern is the temprature at witch the engine is running at.

the water is cold being winter time. about 45 degrees or so.

when the boat is idleing through no wake zones the guage reads about 1/4.

when I run the boat on the top end the guage runs up to about the 1/2 way mark or just a bit more.

how can I ensure the operating temp is ok?

dose the over heat alarm go off well before the temprature too hot?

thanks for any infomation.

Jim

 

[achris]

Re: 1986 175 HP black max v-6

I got it back on the water today.
now my concern is the temprature at witch the engine is running at.

the water is cold being winter time. about 45 degrees or so.

when the boat is idleing through no wake zones the guage reads about 1/4.

Check (read 'replace') thermostats at the top of each cylinder head.

when I run the boat on the top end the guage runs up to about the 1/2 way mark or just a bit more.

That sounds about right.

how can I ensure the operating temp is ok?

dose the over heat alarm go off well before the temprature too hot?

Yes.

The design of these engines is that they should run hotter at lower speeds. In the initial design stage Merc engineers found that if they ran cold at low speed they would foul plugs. So they put thermostats in each head to keep the low speed temp up. Once you open the throttle and the engine speed is higher than about 1800rpm, then the water pressure from the pump (in the leg) is high enough to open a poppet valve setup, on the lower starboard side of the engien block, and the system becomes 'full flow' and achieves maximum cooling. Hence the temp should be lower at higher engine speeds.

Hope this helps,

Chris.....

 

[jigmister]

Re: 1986 175 HP black max v-6

poppet valve a common failure?

I use the boat for fishing water that is FULL of vegetaion and weeds.
Iam SURE the engine sucks up some weeds. in fact alot of times I have so many on the prop I have to run the engine in reverse to clean them out.

what is the best way to flush the cooling system? I once had a merc 4 stroke that had a provion for a garden hose right on the tell tale.

how can I back flush this old merc?

thanks again. hope I am not asking too much stuff.

Jim

 

[achris]

Re: 1986 175 HP black max v-6

First of all... Could you post your engine serial number. At the moment I'm just guessing to get the right drawings.... thanks.

ok... Welcome to the wonderful world of the poppet. I have posted another drawing (Hope it's the right one, see above.)

The poppet diaphragm is # 15 and the poppet valve itself is #20. The water flows through #21 and when the pressure is high enough the push spring #18, #20 opens and nice cool water heads for the heads. Servicing is not too difficult, just use new gaskets. #43 is the cover and #17 is the 'body'. If you buy a service kit be absolutely sure that the spring is exactly the same as the original. They changed the spring tension and the new ones have a stronger spring (water pressure can't open the poppet, engine runs on thermostats only, not enough flow, engine gets too hot...) you get the picture.... I got caught with that a few years back, had me pulling out what little hair I had left for ages.

Cheers,

Chris............

 

[jigmister]

Re: 1986 175 HP black max v-6

serial# 0A960011
model# (according to the merc site) 1175726


This is cool stuff.
mechanical junk is my nature.