"73"850 thunderbolt manafold leaking

bobbya

Cadet
Joined
Feb 24, 2004
Messages
14
hi, new to this site ,hope you can advise me on problem!here goes, 2 pinholes in exaust cover,losing water[alot],started to remove,im up7 bolts to 6 broke ,problem ,cant get to bottom 4 cowl in the way. disconnected cables,wires ,and alot of stuff i probobly didnt have to,any ideas would really help!!!!thanks....
 

andrewkafp

Lieutenant Commander
Joined
Mar 15, 2003
Messages
1,668
Re: "73"850 thunderbolt manafold leaking

If you would have visited iboats prior to dismantle, they would tell you that you WILL break bolts, both on water cover and exhaust.<br />Some would have said, as it's low pressure, you could have cleaned around the pinholes and stuck some JB weld or higher temp putty im 'em and BINGO :eek: Problem gone.<br />But Hindsight is a marvellous thing and you will need to remove the powerhead, drill out the stud with good supply of good quality drill bits and re-tap (Must be drilled centrally)..<br />On the bright side.. When you get the corroded parrts off, and repair or replace them, you will never have the problem return in our lifetime..<br /><br />Well .. mine anyway ;)
 

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: "73"850 thunderbolt manafold leaking

Trying to tap stainless out of alum block is very difficult and usually even if you drill the bolt out perfectly the tap will bind in the stainless shards and chew the holes up to the point where you can't retap to the original 5/16-NC size.<br /><br />I've had a lot better success by drilling out the stainless bolts entirely and installing Heli-Coils in all the affected holes.<br /><br />As indicated you must remove the powerhead to fix this correctly. Better to have it laying on the bench on its side when you drill. Better yet, do it in a drill press. Use new, sharp bits so they run true. Titanium or stronger work well in stainless and you'll need lots of cutting oil. You can get a Heli-Coil kit at most auto parts stores.<br /><br />Use a lot of caution on the remaining bolts or you'll likely break more of them. Get a propane torch and apply heat to the bolts, this may help loosen them. Try working the bolt carefully back and forth to break it free. Don't reef on the wrench too much or you'll stretch the bolt too far and it'll shear off as you've already experienced. Once you get it broken loose, an application of penetrating oil may help. But nothing will dissolve the salt deposits, which mechanically bind the bolt in place. Heat is your best friend when trying to get them loose.<br /><br />Don't forget to replace your inner exhaust baffle too because it'll be in similar (or worse) condition as your outer cover. Check very carefully the inner water jacket cover around the exhaust ports, as if this one leaks it'll blow water directly into the ports. So will the inner exhaust baffle (plate) if it leaks.<br /><br />The inner and outer covers must be properly torqued upon reassembly or they'll leak. Recommend getting a good repair manual (Seloc is one) that covers your motor.<br /><br />I use a light coating of Permatex #3 aviation gasket dressing on all the exhaust plate bolts. This acts as a barrier to keep salt from building back up in the threads. They always will come right apart later on if this is done.<br /><br />While you have the powerhead off, take a look at the condition of the seals in the bottom crankshaft bearing end cap. Very common to see bad seals on 850's, which can cause loss of crankcase compression resulting in poor idle; also water gets sucked into the bottom of the motor which eats up the internals. You can pull this bearing cap off and replace the 2 seals and cap o-ring wihout having to split the crankcase.<br /><br />HTH and Good Luck.
 

Hank 911

Seaman Apprentice
Joined
Feb 2, 2004
Messages
44
Re: "73"850 thunderbolt manafold leaking

Bobbya, I had the same problem with those bottom bolts in the 850 I used to have. Us I used a sabre saw to cut an acess hole about 3"X4". When I got ready to put it back together I cut a piece of sheet metal slightly larger than the hole. A little black paint a screw in each corner and I'm back in business. Didn't look half bad. To extract the broken bolts I drilled out as close to center as I could then used a Dremmel tool with a diamond bit to cut away until I could use needle nosed pliers to get out the rest of it. Takes time and patience. A large heavy hemostat is also useful. I had to helicoil a couple of the holes but the motor is still running good going on 2 years. Hope this helps. :D PS: I used a hammer and nail set to get the pieces where I could use the needle nose.
 

bobbya

Cadet
Joined
Feb 24, 2004
Messages
14
Re: "73"850 thunderbolt manafold leaking

hi again,thanks for the info,kinda had a feeling i would have to remove powerhead that s----s ...oh well,so i guess i'll give it a go and try to fix thanks again!!!!!
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: "73"850 thunderbolt manafold leaking

IF you can get the plates off and there is a little of the stud sticking up. You can screw a SS 5/16 - 18 nut on the stud and then WELD it in the middle. Then you get a second shot at the stud. Use penetrating oil and whack the nut gently side to side before turning. Also heat the block around the stud too.<br /><br />It's WORTH it to take it and PAY fo rthe 10 minutes of welding. I can get 7 out of 8 that way usually. <br /><br />What breaks again you have to drill out and helicoil. CARFULLY :) <br /><br />-W
 

Merc805

Petty Officer 1st Class
Joined
Feb 14, 2004
Messages
202
Re: "73"850 thunderbolt manafold leaking

I suppose that back in 1973. Mercury couldn't have imagined that this corrosion problem would come up 31 YEARS LATER... :eek: <br />Stuff made these days won't have these problems, because all the plastic will have de-composed in 10 years.. :D and the motors will be scrap metal.
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: "73"850 thunderbolt manafold leaking

I work on a LOT of 70's inline 6's and find this problem on a regular basis. It's not a "design flaw", the motors just live too darn LONG! LOL<br /><br />-W
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: "73"850 thunderbolt manafold leaking

Take the block to your friendly neighborhood machine shop and let them worry about the swisted bolts. They got tha right stuff.<br /><br />c/6<br />Hooty
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: "73"850 thunderbolt manafold leaking

If you do - stuff the exhaust ports real well so they don't drop crap in it. If you have the powerhead off anyway, might wanna re-ring it though.<br /><br />-W
 

bobbya

Cadet
Joined
Feb 24, 2004
Messages
14
Re: "73"850 thunderbolt manafold leaking

wow,never thought I would get this much feedback!!!thanks alot!! I'm not a mech but I do understand what your telling me,how long does it take to remove powerhead?do i need any special tools?I have a repair manual for ref,nerver got this far into motor job usually it's electrical problem!! can you explain more about seal? love the welded stud idea, my bro can weld for me :D
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: "73"850 thunderbolt manafold leaking

You'll need the manual.<br /><br />If you don't wanna open it up (for rings) you can remove it dressed without special tools. It'll take you about 2-3 hours the 1st time. <br /><br />As far as the lower seals go, you have to get the bottom end cap off. That's three bolts and then the fun is getting it out. It's best to rotate it a bit with a rubber hammer but be carefull not to break the 3 ears. OR just take it to a shop and get them to pull it. The new seals go in lips down and you need to fill the area between them with grease for best life. It calls for 2 seals but you can get three in there.<br /><br />-W
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: "73"850 thunderbolt manafold leaking

And Hooty is right. The ones that don't come off via the welded nut method outta go to a machine shop to get drilled and helicoiled. It takes a special kind of patiance and steady hand to drill them out and helicoil the holes back to 5/16 - 18<br /><br />I do my own NOW - but didn't when I started. If you screw up a hole, your screwed.<br /><br />-W
 

bobbya

Cadet
Joined
Feb 24, 2004
Messages
14
Re: "73"850 thunderbolt manafold leaking

Hey thanks alot guys for the 411 on this "73" Gonna get a rack, and tackle it tomorrow!!!! Keep an eye out ,I might need more info THANKS ALOT!!!!
 

elcamino12sec

Petty Officer 3rd Class
Joined
Jan 17, 2004
Messages
82
Re: "73"850 thunderbolt manafold leaking

Junk it and but a new supercharged tower of power, Im sure they have alot more bolts that you can break in 15-20 years.
 

bobbya

Cadet
Joined
Feb 24, 2004
Messages
14
Re: "73"850 thunderbolt manafold leaking

hey elcomino,yhay idea has crossed my mind but,,I'm out of work right now cash is slow!!!!! I'd be more than happy to recieve a gift!!!
 

elcamino12sec

Petty Officer 3rd Class
Joined
Jan 17, 2004
Messages
82
Re: "73"850 thunderbolt manafold leaking

I know, its a great idea, I will tell them to send you one after I recieve mine, ok?
 
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