Mercury thunderbolt 115 hp

[crashagn]

I have a Mercury thunderbolt 115 hp inline 6cylinder that ive gotten for free.. including the boat and trailor. The previous owner told methat the engine always ran strong and was serviced everyyear. But has been sitting in the barn for 5 yrs or so. So far ive had the boat/engine garaged since ive had it for the last 3 years. Well now its time to see what its gonna cost me to fix everything up. 1st off is to get the engine running... most of the wiring on the boat is dryrotted and needs to be replaced. No problem, i can do that but whats bugging me is locating the seriel number for the darn thing. The only # i have found is on the steering tube 3761508. I have searched and searched and have powerwashed almopst everything and still cannot find anymore info on this engine. What iam looking for is knowing what yr this thing is, after that then i can start looking for diagrams and so forth.. Any help would be appreciated

 

[Laddies]

Re: Mercury thunderbolt 115 hp

I believe that is the serial number it would be a 1974, it would be the 473rd engine built in 74

 

[crashagn]

Re: Mercury thunderbolt 115 hp

Thankyou so much for the reply Laddies. The only other thing bothering me with this engine is that ive heard if the top end fails thats it.. its pretty much shot. But ive also heard it can be bored out to get around 135hp. I did a compression test when i did get the boat and the only cylinder that was low was the very bottom 1, and it did have a very slow leakdown. Ill retest all 6 and post the reults when i manage to get a new 6 volt battery, or ill use the pull rope..

 

[Clams Canino]

Re: Mercury thunderbolt 115 hp

Do an Ebay search on *Mercury Internal Wire Hareness* for a step forward with wiring.

See my Timing and Sync post in the FAQ here for some tips

-W

 

[Scaaty]

Re: Mercury thunderbolt 115 hp

Thankyou so much for the reply Laddies. The only other thing bothering me with this engine is that ive heard if the top end fails thats it.. its pretty much shot. But ive also heard it can be bored out to get around 135hp. I did a compression test when i did get the boat and the only cylinder that was low was the very bottom 1, and it did have a very slow leakdown. Ill retest all 6 and post the reults when i manage to get a new 6 volt battery, or ill use the pull rope..

Its a 12 volt system, not 6, and 115 Mercs of that vintage were just 135hp motors, with some restrictor stuff to knock it down to 115 instead of building a whole new motor to meet the hp need...own one that was a orig 115, and its back to 135 after a crank up rebuild....from my books on it... "The '72 1150 is a choked down 1350 with a few flow restrictions to give the lower HP rating so Merc wouldn't have to come up with a different powerhead to fill that HP range for the consumer market."..

 

[crashagn]

Re: Mercury thunderbolt 115 hp

If i may ask, why is there a sign on the back saying direct 6 charge? or that just refering to the inline 6 of the cylinders?

 

[Chris1956]

Re: Mercury thunderbolt 115 hp

"Direct Charge" is the trade name for Mercury's Cross flow motors.

Make sure that motor has clean carbs and a new water pump impeller. You might rebuild the fuel pump (s) as well, and do the link and sync of the carbs and spark advance.

 

[crashagn]

Re: Mercury thunderbolt 115 hp

I was planning on getting comlete rebuild kits for the carbs.. float and needle and seats as well. Might as go all they through them since they will be off. And also the impeller. Ill have to invest in a wiring harness also. Just did a compression test earlier and the avg on the cylinders was around 80-90. Also the spark from the plugs is very strong

 

[Chris1956]

Re: Mercury thunderbolt 115 hp

80-90 PSI is a bit low for that motor. If it is consistant across all six, it is likely OK