Replace these MGB pistons?

[CrutyRammers]

Evenin' all.
I'm in the process of rebuilding a 'B. '77 rubber bumper model.
The camshaft is scrap, a couple of the lobes are worn down several mm and the followers are pitted to buggery. However I can't find any ovality in the bores or crankshaft journals which is nice.

The pistons are showing signs of rubbing down the sides, and a couple have pitting on the crowns. They measure up fine, as far as my measuring goes, but I'm tempted to change them out. What do you guys think?



Of course, if I'm going to change them anyway, I may as well go a bit oversized; it's only a few hundred quid for a set of pistons and a rebore so I'm thinking why not? I need to replace the cam, and am going to get the head modified anyway.

[PeterBurgess]

For the cost you may as well do it for peace of mind.
The black dots almost joined up on the thrust faces look like it has been running too rich.
Peter

[Mignon]

Measure the ring groove widths. There should not be more than 4 thou play (feeler guage) to a new ring. Also pin bore diameter. If these are ok I see no point changing them. A light hone and new rings shoould suffice.

[CrutyRammers]

Thank you both.

[tapkaJohnD]

What about bore wear? If there's a ridge at the top, then you may have to rebore and buy oversized pistons anyway.

John

[Mignon]

CrutyRammers said:

Of course, if I'm going to change them anyway, I may as well go a bit oversized

Extra capacity is essentially immaterial in terms of power production. You get a bit more torque but at lower revs. That's about it. Extra airflow is what matters. Constructive portwork, backcut valves, a bit more cam duration and lift are far more cost effective.

[Peanut Gallery]

Mignon gets my vote - if it aint broke..

That said, check your bores, and check them in lots of places.

Btw, I am still patiently waiting for your http://www.alfadax.com/ to be updated with MG progress!

[CrutyRammers]

Peanut Gallery said:

Mignon gets my vote - if it aint broke..

That said, check your bores, and check them in lots of places.

Btw, I am still patiently waiting for your http://www.alfadax.com/ to be updated with MG progress!

Yeah, I've kinda failed at updating the website. Too many other things to do. But involved welding, lots of welding...

[Boosted LS1]

Would it help to polish the scores on the skirts with some fine wet and dry?

[99hjhm]

You will be lucky to find an MGB engine in this age that doesn’t want a rebore. I agree by the look of it the pistons don’t look too bad.