rebuilding powerhead

[jason1150]

I'm working on my old powerhead, it's a 72 mercury 1150, I had bought 3 new pistons, all new rings, gasket kit, but I didn't pull the exhaust plate till it was too late and I found a crack in one of the exhaust ports, so I got a used powerhead on ebay but I want to fix up the old one, so I had a welder weld the crack, bored one cylinder, honed the rest, got a new exhaust tuner plate I think it's called, now all that's left is too do a little porting on the weld and clean up the engine for reassembly.

what's the best way to clean up the old pistons and exhaust cover plates, I've got a small sandblaster, I tried it on the scored piston that I'm replacing and it worked great, was thinking of doing them all and then sanding them with fine sandpaper, I've got a little steamcleaner that I'm going to try but I kinda doubt it will do much, thanks, Jason

 

[achris]

Re: rebuilding powerhead

Don't sand pistons... Don't use anything that will remove metal, that includes sandblasting. Use a solvent. I use Merc Power Tune to loosen the carbon and then just wipe them with a rag. Use an old broken, sharpened piston ring to clean out the ring grooves.

Chris........

 

[jason1150]

Re: rebuilding powerhead

thanks Chris, will do, Jason

 

[monk-monk]

Re: rebuilding powerhead

i have read other Threads about this "exhaust" plate and cracks in it, what is it, where is it located...how can i educate myself on this subject to inspect mine, i have the same 1150 motor. i do have a Factory manual to refer to if needed!

 

[jason1150]

Re: rebuilding powerhead

here's the crack that I had welded in the exhaust port, I still need to clean up the weld on the inside, I had the guy groove a "V" where he welded so that I could grind it down without getting into the crack, the plate I bought new, I don't have any before pics but I can tell you the crack was through the plate and the port

here's the pistons and one of the tools I'm going to use to install the pistons into the block, I haven't made the offset ones yet but you get the idea

 

[jason1150]

Re: rebuilding powerhead

It's worth a try since I already have all the parts just lying here

 

[Laddies]

Re: rebuilding powerhead

Jason, that ring compressor shows a lot of ingenuity congratulations for figuring that out.

 

[emckelvy]

Re: rebuilding powerhead

Jason, that was a nasty crack in the block! Looks like you've got it welded up pretty good though.

What you really need to do, however, is to have that entire surface milled flat. Otherwise it won't seal properly, and will dump water into the exhaust ports.

Once you have the inner sealing surface milled, be sure to instruct the machine shop that the outer surface of the block (where the exhaust plate and outer exhaust manifold cover bolt up to) must be milled down the same amount as the inner surface was taken down.

So, for example, if the inner surface is milled .010" to straighten it up, machine the outer surface .010" also.

This does (2) things: ensures the relationship between the exhaust plate and the inner water jacket cover remains unchanged; also it gives you an excellent new sealing surface on both.

I've had this done for years to blocks, by a master machinist who came up with this method of fixing blocks which had the inner sealing surface messed up.

They always came back looking beautiful and never leaked.

One last thought, depending on how the sealing surface at the back of the block looks, you could have that surfaced also. Thus guaranteeing a leak-proof repair!

Cheers and G'luck on the rebuild.............ed

 

[jason1150]

Re: rebuilding powerhead

that's really helpful advice, I had told the shop to check it for warpage and to not machine it if it was okay because I was worried about it not sealing because of a gap, but machining both surfaces is brilliant, the only problem I can see with this block is that the welder could not weld inside the water jacket because it was too small, the crack went around into the water jacket, it doesn't look like it goes all the way down, I'm a little worried that the heat could pull the water down around the cylinder sleeve, what do you think?

 

[hamit59]

Re: rebuilding powerhead

Jason,
I would use a flap wheel to polish the port back to smooth up the welded surface. I don't know what to tell you about water jacket. My thinking if the welder got good penetration on his weld, then you should not have anything to worry about. Milling the mating surface is a great idea but you need a record finish when the machine work is done. This will give you a good grip to hold the gasket in place.
just my 2 cent worth

 

[jason1150]

Re: rebuilding powerhead

thanks Hamit, wouldn't of thought of that, "record finish", very much appreciated, what's a flap wheel? Jason

 

[jason1150]

Re: rebuilding powerhead

okay, I googled flap wheel, now I just got to get the right size, maybe 1"

 

[hamit59]

Re: rebuilding powerhead

1" to do that work would be fine start at 80 grit and go to a 180 or 220 grit that should be all you need for that job. Your not looking for a polished finish.
I use a die grinder to power flip wheels. You can use a drill it will just be slower.Try to match the radii of the other ports, without removing too much metal. After looking at the pics closer you do not have a lot of work to do there and your welder is pretty good. I think I would do a dye penetrate test to see if the is any other cracks before you put is all back together.
I think you have a good runner when you done. I love the ring compressor
My set I spent well over 400.00 for them back in the 80's

 

[jason1150]

Re: rebuilding powerhead

thanks again Hamit, my welder is a really nice guy, every time I bring him something he only charges me 10 to 30 bucks, that weld cost me 30, I usually do my own welding but there is no way I could do what he does.

this site is awesome, thanks, Jason

 

[hamit59]

Re: rebuilding powerhead

Jason you got the deal of the year there. I would think he had over two hours in prep time and welding. Did you find the flap wheels you need? If not look for
a machinist supply.
best of luck