Boring a '78 Mercury 800

[1970Thunderbird]

Hey fellas,

My motor came apart quite easily. I flew it up to Poplar Bluff, MO yesterday and handed it over to the machinist. He's already bored the first three cylinders to 15 thousandths over standard. While boring the fourth cylinder, he discovered a gouge. In order to get the gouge out, he bored that cylinder to 30 thousandths over standard. He said he'll put in whatever pistons I tell him.

My gut says all four cylinders should have the same bore, which means boring the first three out to 30 thousandths over standard. However, the machinist has said he's bored cylinders differently in the same engine before with no ill effect. What are your guys' thoughts? Should I run it with a different bore in number three, or have him bore the entire motor to 30 thousandths over?

Also, he said he's not fond of Wiseco pistons, as they tend to expand more when heated. He mentioned the Pro Pistons and seemed to like them. What pistons do you guys like?

As always, thanks for all the help. Couldn't do it without you guys.

 

[ricohman]

Re: Boring a '78 Mercury 800

When I worked a a mechanic for a large GM dealer we used to get the odd iron duke Fiero or Citation ect with piston slap.
The factory cure for these new cars was to bore the offending cylinder and fit a new piston. And yes, it was usually 10 over.
We would stamp the piston 10, 20 or what ever it was and put it back together.
I know those motors lasted as we would see them come back for other things as the years went on.

 

[Faztbullet]

Re: Boring a '78 Mercury 800

It is ok it mix/match pistons in a 2 stroke as they are made to weigh the same. I myself dont like Wiseco but use them in a pinch. I perfer the Persan, Pro Marine and WSM, Wiseco,Sierra and GLM only if I have to. Inline pistons are starting to get hard to get in certain sizes...

 

[1970Thunderbird]

Re: Boring a '78 Mercury 800

Fatz,

I'm going with Pro Pistons, I think. They have a coated version called the Pro-V? Basically, they're coated in Teflon to help protect them during the break-in process. Is it worth the extra $20 per piston?

Also, if it were your motor, would you mix/match, or bore them all to the same?

 

[Faztbullet]

Re: Boring a '78 Mercury 800

In my opinion no as its worn off the skirts in about a hours running time. Clean the block throughly and use double oil and it will be fine..

 

[1970Thunderbird]

Re: Boring a '78 Mercury 800

You mean run a 25:1 fuel to oil mix? For how long? In other words, what's the proper break-in procedure?

 

[hotrod53]

Re: Boring a '78 Mercury 800

Back in the day I wouldn't use Wiseco pistons in my dirtbikes, they didn't last. That and they were a 1 ring piston vs a 2 ring piston. I used Pro X pistons in my Honda and Kawasaki bikes and loved them, not sure if that is the same mfg or not. Either way, nah on Wiseco.