26 CHECKMATE

Last year I had a blower put on my 7.4l motor, I did allot of research prior to putting it on and came up with allot of different answers. Some people said the motor would live and some said it wouldnt. So I whent to a local motor shop and asked a guy that everyone recomended I talk to. He assured me that as long as I did a valve job and changed the cam and carberator it ould be fine. So I gave him $4000.00 and he set it up for me. Five hours into running it I heard a noise from the engine compartment so I took the boat in for him to look at. We came to the conclusion that I burnt the #4 piston, spun three main bearings and a rod bearing. He told me that that he wasnt sure what had happened but he thought since the original equipment was still in the lower end it could of just not have been able to handle the boost or the exhaust was leaking into the cylinder. So I gave him $4500 to rebuild it and then whent out and bought a new set of stainless marine exhaust. Well i got it back and spent 10 hours breaking it in I changed the oil and took it out to test it and it burnt another piston. So I talked to the guy who put it together and he told me it must be a lack of water pressure. When he had it out the last time I put a new water pump on it and checked the pick up out and it was fine. So I took the motor apart todayand when I pulled the head off I noticed there was oil in the water jacket so now I think in addition to burning the piston I must have cracked a cylinder wall.It wasnt a whole lot of oil but it was enough to notice. The motor guy told me I should just put a factory motor back in it but after spending $11000 to step up to something more I dont want to go back to what I had in the first place. Can anyone give me some ideas on why my motor is doing this and what can I do to prevent it. Could it be the cam is to small which would be creating to much compression in the cylinder or could it be water pressure. I am hoping I wont have to pay again to have this thing fixed but whether I do or dont I just want it to run. As always any help is appreciated.

John B

Without more information it seems most likely your motor is running too lean, a very common problem with blower motors. You didn't tell us what you or your mechanic did to the fuel system, either initially or after you burned the first one up. Water is not the cause of burned pistons and bearing destruction.. You need a new mechanic, or at least one who knows boat supercharging. Call the blower manufacture and ask for their recomendations or tell us about your fuel system, timing, compression.
JB

Griff

What blower did you use and how much boost???? A 7.4 with cast pistons is not going to handle much boost. 4-5 lbs max with only short WOT runs.
Who do you keep handing all this $$$$$ over to only to have him not do it right??

sgrady

What kind of set up did you use and what delivers the fuel ? Also where are you located ?

KAAMA

Make sure you take your engine to someone who understands what it takes to make a MARINE engine survive. I am not saying this is so in your case and there are exceptions to the rule, but in most cases engine builders/mechanics for cars usually do NOT have a clear understanding of this. Sometimes they will respond and say; "Hey, I've been building engines for 20 years!" but these same kind of guys don't understand some of the requirements for a marine engine's performance and more importantly it's survival. And it's like you can't tell them a thing! I've seen some dissasterous results happen to a few boaters. Find someone who is reputable, has experience and is a little savy with building/repair of marine engines. I hope things turn out well for you.

26 CHECKMATE

Just to give you a little background when I first did the upgrades I put a wieand 177 blower on running 5 pounds of boost and not for long runs mayby 30 seconds at a time. When I did the upgrades I did change the carburator to a 850 cfm holley 4 barrell and changed the mechanical fuel pump to a holley electric fuel pump. When I did the last rebuild I actually fattened up the jets so I would assure myself I wouldnt have this problem again. As far as the timing it was set at 30 advance and the compression was 9 to 1 I believe. When I took the heads off the tops of the pistons and the tops of the cylinders looked like they were running to rich. Could it have anything to do with the intake manifold having rectangular ports and the heads having oval ports I was thinking that mayby some of the fuel wasnt getting to that cylinder. The guy that is doing the work comes highly recomended for building good solid boat motors he has built allot of marine motors and everyone is very happy with him. He himself runs 900 hp turbo motors in his own boat.

mopower

26 Checkmate,
You upgraded the fuel pump , but how about the fuel lines(including the tank pickup and water sep. filter Are they still the original? I have drilled out and retapped the fuel filter and replaced pickups in tanks. It could be rich at slower speeds but going lean at top end due to lack of fuel flow. Also I'd look at that 30 degree advance a little more , remember with 5 lb its no longer 9 to 1 , you could also be detonating the motor. Good Luck

26 CHECKMATE

I upgraded all of the fuel lines with bigger lines and I put on a higher volume fuel pump I didnt do anything on the pick up in the fuel tank. What can I do to change that it is not very accesible.

mopower

My last boat the fuel pickup was accessible through the lift out panel in the floor.I tapped the hole out bigger and changed the 90 degree elbow to a larger 45 degree and soldiered a larger draw tube to it. Also drilled 90 degree elbows are resrictive to fuel flow . 45's or better yet curved are better. You didn't mention your water sep. filter. Be sure to drill all the way in to the center (not just the end for a bigger fitting)

26 CHECKMATE

I did change the water seperator and put on a high flow filter