First Time Poster, Cracked Manifold on I6 90HP Merc

[blue90HP50]

I bought used '82 Merc I6 90 HP last year, have done all needed to get a stored motor back up. Went to lake, thought one cylinder was down but all have good compression, fuel and spark. Just starting at top carb mount and angling around the enrichner valve mounts there are "Hairline cracks" where fuel vapors are escaping and blowing all over the front. A (mechanic?) told me this was a sign of an impending rod failure. Another said this was heat related. Manifold/block fronts are not interchangeable, is this correct?
By the way, from a rough WOT to Throttle-down I did hear a distinct different noise develop. Any thoughts would be appreciated. Decision time!

Regards, blue90HP50

 

[Chris1956]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

That is an unusual story. However, the crankcase covers (Inline Mercs do not have intake manifolds) are not usually interchange due to their necessary precise fit in order to seal.

I have never heard of hairline cracks in them, and the cracks if they do exist, are not the result of overheating. That is the cool part of the motor. Also, I think they are unrelated to the condition of the recripocating portion of the motor. Perhaps someone had the cover off and incorrectly installed it and cracked it?

Can you post some pics of the cracks? You might get them welded

 

[daveswaves]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

That is an unusual story. However, the crankcase covers (Inline Mercs do not have intake manifolds) are not usually interchange due to their necessary precise fit in order to seal.

I have never heard of hairline cracks in them, and the cracks if they do exist, are not the result of overheating. That is the cool part of the motor. Also, I think they are unrelated to the condition of the recripocating portion of the motor. Perhaps someone had the cover off and incorrectly installed it and cracked it?

Can you post some pics of the cracks? You might get them welded

I agree with Chris, the intake covers do not generally crack unless they have been abused. If a rod breaks it can obviously crack a cover, however, that is not the case here.
I have had reasonably good success interchanging covers,but, thats because I have lots to choose from and I pick a cover that fits the block nicely. There is a difference between the ADI covers and the older distributor covers, they are not interchangeable. One thing for sure, if you have a crack that is spraying fuel you are also sucking air and that will lead to a lean condition and melt down of pistons. Try and post a pic.

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Thanks to both Chris and Dave. Pictures in camera, but posting pictures is foreign knowledge to me. Nice looking boat and I6 Dave.

Sorry, I will get more fuel and let idle on muffs tommorrow, and take more pictures to try and show the fuel escaping. Also, I put snap-ties on both lines on enrichner valve, they were loose, might be part of the problem. But there are some cracks.

Thanks again.

 

[daveswaves]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Thanks to both Chris and Dave. Pictures in camera, but posting pictures is foreign knowledge to me. Nice looking boat and I6 Dave.

Thanks, that particular I6 is a 1986 block with a 1975 front cover running a distributor. It is possible

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

I'm back to the original thread. JB Welded cracks, not sure it's working yet.
I'm ready to pull powerhead to re-gasket exhaust cover, cylinder cover, and install bleed restrictors. Should I drop lower unit before loosening the powerhead? Powerhead is attached to lifting device. Dropping the lower unit is not a problem for me, just want to know if it is necessary. Any advise is greatly appreciated.

Blue

 

[Droll]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

I'm back to the original thread. JB Welded cracks, not sure it's working yet.

If not you might try this product , relatively easy to work with...

Should I drop lower unit before loosening the powerhead? Powerhead is attached to lifting device. Dropping the lower unit is not a problem for me, just want to know if it is necessary. Any advise is greatly appreciated.

It's not needed since you got some sort of lifting device, without any lifting device it could simplify the job some but it's still not needed .


Arne Kjetil

 

[Chris1956]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Blue, I always remove the LU before pulling the powerhead. The reason is that you need to align the driveshaft with the crankshaft. I have never felt comfortable doing this while trying to lower a heavy block onto the midsection. I was always more comfortable pushing the LU into the midsection, after the powerhead was installed, since I was sure I was not strong enough to wreck the splines in the crankshaft or driveshaft.

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

1982 I6 90HP, I Dropped LU yesterday, got powerhead off, removed exhaust cover and baffle, cleaned. Today, problems, water cover at plugs, all 16 bolts broke off. Spent day drilling etc. got cover off, more drilling, got 4 holes tapped. Is this normal? 12 to go. I planned to install new bleed restrictors. Will the bolts on that cover be the same trouble as the water cover at the plugs? If so, I might re-think the new bleed restrictors. paragraph: I never thought a motor could have so much sand and salt in it, it is unthinkable the neglect this motor has seen! As always, any advise is appreciated. I see the forum is getting busy these days.

Blue 97 degrees in shade today

 

[AMD Rules]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Bolts on the starboard side intake transfer ports are typically not a problem.

The port side exhaust covers and water jacket bolts can be a bear, as you've found out.

Good luck, and please post your final results. Interested to know how you make out.


.

 

[Chris1956]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Blue, On some blocks you may drill thru the block at the head water jacket cover, and install nuts on the screws that hold the cover on. Look carefully to see if you have clearance.

Breaking 16 bolts may be some kind of a record, and may indicate salt water usage. I would postpone removing the exhaust covers until you are absolutely sure you need to. If you need to remove them use a torch to heat the bolt head very hot. Remove heat and spray with PB Blaster and let cool. Now reheat (watch for fire) and put hand impact wrench on bolt head and smack it firmly, but not hard. See if you can coax them out. The inner water jacket bolts are much worse to remove than the outer water jacket cover.

 

[Inline6]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Just throwing 2 cents in. Welding will result in distortion to some degree. Given the need for a tight fit my gut feeling is welding is not practical unless it can be followed by machining to flatten the affected surface.

Trying to match another manifold seems to be a more viable option?

Regards,
Inline6

(American Welding Society Certified Welding Inspector)

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

I'm back. Spent yesterday and today drilling/tapping broken bolts/holes. Went pretty well except center hole on bottom on water cover/block; broke off tap in hole and cannotremove the broken piece. Any ideas? I'm thinking of filling it and make a cross brace from the two botton bolts to the omitted bolt. Should I remove the inner exhaust cover for inspection at this point?

Again, Thanks, Blue

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

I'm back from short absense, Thanks, ('82 Merc I-6 90HP) Replaced water jacket cover, hope its OK. Removed transfer covers, no problem. While the covers were off I saw the Hairline Cracks on the inside of the crankcase cover at #2, and possibly #3(can't remember) and felt some slight movement of rods on crank when I applied pressure vertically with my thumb and forefinger. Nuts are secure on rod bolts. Also, I hear a noise when I "turn flywheel back and forth a fraction of an inch. Compression was good before removing PH from midsection, I wanted to visual inspect and re-seal.
I bought top bearing and seals, and bottom bearing and seals, but have not installed. Pistons, rings, and cylinder walls look good where I could see, evidenced by good compression. Sum, I need advise and/opinion on the status of rod and crank bearings. Should I wait and replace them when $ is available, go ahead and replace top and bottom bearings and re-seal and reassemble to run, or worst case, scrap the project?
All input is greatly appreciated. Sorry for length of post.

Thanks, Blue

Motor is for '72 Glastron 17'6" Swinger Aqualift

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

I'm back from short absense, Thanks, ('82 Merc I-6 90HP) Replaced water jacket cover, hope its OK. Removed transfer covers, no problem. While the covers were off I saw the Hairline Cracks on the inside of the crankcase cover at #2, and possibly #3(can't remember) and felt some slight movement of rods on crank when I applied pressure vertically with my thumb and forefinger. Nuts are secure on rod bolts. Also, I hear a noise when I "turn flywheel back and forth a fraction of an inch. Compression was good before removing PH from midsection, I wanted to visual inspect and re-seal.
I bought top bearing and seals, and bottom bearing and seals, but have not installed. Pistons, rings, and cylinder walls look good where I could see, evidenced by good compression. Sum, I need advise and/opinion on the status of rod and crank bearings. Should I wait and replace them when $ is available, go ahead and replace top and bottom bearings and re-seal and reassemble to run, or worst case, scrap the project?
All input is greatly appreciated. Sorry for length of post.

Thanks, Blue

Motor is for '72 Glastron 17'6" Swinger Aqualift

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

Friends: Any opinions/advise on this motor? Chris AMD_rules? I need advise! Thanks
blue

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

I've decided to button it up, put it back together and run it! Wish me luck!
Blue

 

[blue90HP50]

Re: First Time Poster, Cracked Manifold on I6 90HP Merc

82 Merc 90HP I-6 Put back together and had water leak at gasket pwhd to midsection. May have found the cause. My question is, The exhaust port on the midsection has a divider, approx 1/4 inch wide. This divider is pitted/corroded to the point I think the gasket will not seal. Although not ideal, is this a serious problem? If so, what are recommended solutions?

Thanks, Blue