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Starting on reconstruction

 
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clay
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1972 Chevrolet Nova

PostPosted: Sun Jun 06, 2010 9:15 pm    Post subject: Starting on reconstruction Reply with quote

Gathering parts for the reconstruction. First I needed to clean up the heads. The intake ports were really carboned up from reversion. I spent about 10 min. with a wood rasp and this is what I got - yeah right. I do think they turned out pretty good though. I didn't do any shape changing, I just worked the CNC marks out and did some blending, but I don't really expect to gain much as I think they were really good to start with - but they are pretty - and that's worth 0.1 right????




Mains looked like they were a little tight - contack pattern seems to wide. My notes said I had just under 0.003" clearance. However when I ordered another set of standard bearings they showed 0.002" clearance. I don't know where the difference is, all I can say is I must have screwed up the first time. I measured the bore in the block - same, crank o.d. - same, bearing shell thickness - same, but there seems to be less clearance this time. Anyway I am putting in a set of "X" bearing to get the clearance right at 0.003" to just a fudge over. They also showed signs of scuffing which is I'm assuming from the lack of oil pressure on shutdown. I have and accumulator to hopefully solve that issue.

Got the crank back in yesterday, hopefully I'll get the short block back together this week or by next weekend. Clay

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squeeezer
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1991 Chevrolet Camaro

PostPosted: Sun Jun 06, 2010 9:32 pm    Post subject: Reply with quote

i thought cnc striping was good?
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af2
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1933 Willys Coupe

PostPosted: Sun Jun 06, 2010 10:03 pm    Post subject: Reply with quote

squeeezer wrote:
i thought cnc striping was good?


It the result of a copy. PTL in AFR's case. Shocked Laughing
Smothed is better.
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Mon Jun 07, 2010 12:45 am    Post subject: Reply with quote

Comment on the bearing clearance. I had to go with .001 over bearings to gain the extra clearance when I built my engine. The std size was a little too tight. Interesting you seem to have had the same issue.
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Big Dave
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PostPosted: Mon Jun 07, 2010 1:44 am    Post subject: Reply with quote

Darian Morgan has stated that a mirror finish actually hurts air flow which is why the wash board finish is left in the ports by the CNC machine in the first place (it could leave a polished finish as it doesn't care what the program tells it to do). The CNC leaves a wash board pattern that is perpendicular to the air flow. The turbulence at the surface acts like a series of rollers to support a column of laminar air flowing air.

If you changed nothing other than polishing the ports it could be a great test to prove him wrong if the car picks up speed on the rebuild.

Big Dave
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clay
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1972 Chevrolet Nova

PostPosted: Mon Jun 07, 2010 8:28 am    Post subject: Reply with quote

Quote:
If you changed nothing other than polishing the ports it could be a great test to prove him wrong if the car picks up speed on the rebuild.

There were problems with the combo, so it's getting a "tweak" or two so there won't be any way to tell if it is good or bad. I see both sides of the flow theory. On the intake side, I can possibly see some breaking up of fuel - maybe. On the exhaust side, I don't see any benefit from the CNC marks. Even AFR offers the competiton port version that has a finer finish and flow does pick up. Here is where it could get iffy - I know outright flow isn't everything - there are other issues also. I think I played it safe with what I did - I might not have helped much but I can't see where I could have hurt anything. Clay

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af2
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1933 Willys Coupe

PostPosted: Mon Jun 07, 2010 6:36 pm    Post subject: Reply with quote

Never said a "mirror".

60 grit on the intake works.
Good to see you left the ski jump in there.

A "mirror" on the chambers and exhaust will help keep them from carbon build up.

But then you can't say it runs better after breaking it in because of more compression with the carbon build up. Twisted Evil
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af2
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1933 Willys Coupe

PostPosted: Mon Jun 07, 2010 6:50 pm    Post subject: Re: Starting on reconstruction Reply with quote

clay wrote:

Mains looked like they were a little tight - contack pattern seems to wide. My notes said I had just under 0.003" clearance. However when I ordered another set of standard bearings they showed 0.002" clearance. I don't know where the difference is, all I can say is I must have screwed up the first time. I measured the bore in the block - same, crank o.d. - same, bearing shell thickness - same, but there seems to be less clearance this time. Anyway I am putting in a set of "X" bearing to get the clearance right at 0.003" to just a fudge over. They also showed signs of scuffing which is I'm assuming from the lack of oil pressure on shutdown. I have and accumulator to hopefully solve that issue.

Got the crank back in yesterday, hopefully I'll get the short block back together this week or by next weekend. Clay


1 thing I have always done is double check with plastigage to check my math. Just a suggestion.
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clay
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1972 Chevrolet Nova

PostPosted: Mon Jun 07, 2010 10:14 pm    Post subject: Reply with quote

It's a great suggestion. Actually last time I did. I wrote down 0.003" with dial bore and 0.002" with plastigage. Evidently the plastigage was right - never said I was perfect. I have read that Joe Sherman removes the ski jump and picks up a good bit of flow. However I'm not Joe (or Darin Morgan) by a LONG shot. I don't have a flow bench and honestly I don't want one. Porting heads is not something I enjoy. Well I do enjoy the first port or two so maybe I need to work on dirtbikes. I didn't polish the ports by any means. That's what's left from an 80 grit cartridge roll. I did sort of polish the chambers and I did polish the tops of the pistons. I used to do that on some of the 2 strokes I worked on. Clay
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Tue Jun 08, 2010 2:03 am    Post subject: Reply with quote

i polished the chambers and exhaust ports on my old iron heads and, IMO, the mirror finish would probably be good for a race car but a street car will carbon up the port and combustion chamber no matter what the surface. it may just take a little longer with the polishing.
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