jb or anyne have an opinion on this head???

829 Views 3 Replies 2 Participants Last post by jbranson, Jun 17, 2005

joe c

Discussion Starter · Jun 16, 2005

check that valve out. all the rest have a nice coating of carbon, but not that one. yes, i know there is some oil, thats from some brake cleaner i squirted in the port to see if it was leaking. comp test was good. didnt bother to do a leakdown on it. but its the right side and its the side i had issues with. it looks like it might have at some point seized a guide, but i havent been over to the shop to drop the valves yet. anyone have an idea of why there wouldnt be carbon on this?? im no tuner building genious, but no one ive asked has an idea.
i should add that the valve is that color. the blackness of it isnt from the brake clean. there is only a small amount of brake clean on it. there is only a little carbon on the face of the valve. just like it looks. the brake clean is around the seat and just above the plug hole. and no, im not reinstalling this head.

jc

me

Edited by - joe c on Jun 15 2005 8:40:11 PM

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jbranson

· #2 · Jun 16, 2005

Hmmmm...
If there are no shiny marks on the piston where the valve was touching then it might not be anything serious.

I've seen these deposits on a lot of street engines...less so on race engines...not really sure what it is. Anyway...if the valve was touching the piston from a seized guide it could knock the deposits off the valve around the edge...but it would also have left a small spot on the piston where it was touching now and then.

Thermal shock would also break the deposits loose...running real rich on that carb for instance...or real lean. I notice the exhaust valve looks a bit different than the other too. Usually I have to go at a valve for a while to get it as clean as that intake around the edges.

I guess also if the guide was seizing it would hold the valve open a bit and it would get hot as it couldn't transfer heat to the seat. Would have been some popping out of that carb when it ran.

Is that plug hole ok? Wasn't stripped was it.

Mary's little 70 is the only engine I've ever seen where you could wipe the pistons and valves with a rag and they would be shiny new again.

Anyway...I got no answers for you Joe...although I wouldn't give up on that head...pull the valves, clean them up, check the seats, put in some new springs and put it back on...looks to be in decent shape.
JohnnyB

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jbranson

· #4 · Jun 17, 2005

I've kind of given up on reading combustion chambers. I've pulled some of my engines apart that were running really well and the chambers didn't look very good. Various deposits, different colors, nothing serious..but not the even, nice colors I would expect from a good running engine.

If you don't already, you might want to try indexing the plugs. With some of these old highish dome piston engines the direction of the plug electrode can make more difference than you might think. Specially with race fuels. If the two of them were pointed in opposite directions it might make for different burn patterns in the cylinders. I index all mine to between about 10 o'clock and 2 o'clock. For both combustion reasons and so they will clear the plug notch in the pistons.

The mating surface of the head looks real good, it's sealing nicely.

I betcha the difference is caused by something in the carbs.
JohnnyB

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