triumphs
[Top] [All Lists]

Minor tale of woe....

To: triumphs@autox.team.net, spitfires@autox.team.net, fot@autox.team.net
Subject: Minor tale of woe....
From: "Michael D. Porter" <mporter@zianet.com>
Date: Wed, 02 Jul 2003 05:19:33 -0600
Delivered-to: alias-outgoing-triumphs@autox.team.net@outgoing
Organization: Barely enough
Okay, I got bit by the local machine shop (the owner is a low-rent circle-track 
racer--I should have known better--but there are only two shops in town and I 
didn't know anything about the other one
at the time).

I'm just now getting back to putting together the engine for the street `70 
GT6+, after too many years of 80-90 hours a week on the day job. I had the 
machine work done years ago, just before I
started putting in crazy hours at work.

I'd asked for a 3-angle valve job, hardened exhaust valve seats installed and a 
total of 0.020" milled from the head (0.003 to clean up warpage and the rest to 
get compression up to about 10.7:1 with
domed pistons, the limit I thought I could manage on premium pump gas and 
well-polished chambers, valves and piston tops). I simply picked up the head, 
paid the bill, took it home, and put it on a
shelf in the garage without paying much attention--by that time, I didn't have 
any time to examine it or finish it up.

Some of the screw-ups I have managed to fix, or will. The hardened exhaust 
seats (probably taken from a diesel catalog) which made the exhaust ports 0.75" 
in diameter, I've fixed with a couple of
hours boring on the milling machine. The single-angle, badly-cut, valve seats I 
can fix once I get the valve cutter set I need. 

But, the real horror I just discovered this past weekend. I'd checked head 
warpage early on, and it was about 0.003" diagonally. A cursory examination of 
the head height before I had it milled told me
it was very nearly stock. I'd bought a set of early domed pistons at +0.030", 
thinking that even if those didn't provide the best power, it was a better way 
to get compression up to 10.7:1 without
over-milling the head, and worrying about collapsing the relieved area around 
the intake ports.

So, this past weekend, finally with more time available, I cc'ed a sample 
chamber. 32cc. Did the calculations without including the dome on the piston 
and came up with 10.62:1. Huh? So, tonight I ran
the calculations with the volume of the dome on the piston included. 14.4:1. 
Did a couple more calculations and it seems likely that the yo-yos at the 
machine shop took off about 0.100"-0.120" from
the head, instead of 0.020". And, after a closer look at the rocker side flange 
of the head, it looks pretty thin.

So, I have two questions. First, what's the list's experience with regard to 
the longevity on the street of a GT6 head milled to that degree, and second, 
does anyone have a new set of +0.030" GT6
flat-top pistons they'd like to swap for a new set of +0.030" domed-head 
pistons? The pistons are pretty much what was available at the time from a few 
vendors--AE, with the usual aftermarket ring set
(not gapped yet), bought new from BPNW quite a few years ago. I paid $260 for 
the set on closeout. Not concerned about an advantage on the relative swap 
value; I just don't want to have to convert it
to diesel to make it run with those pistons. (!)

Yeah, I know... drat.

Cheers.


-- 
Michael D. Porter
Roswell, NM 
[mailto:mporter@zianet.com]

Never let anyone drive you crazy when you know it's within walking distance.

///  triumphs@autox.team.net mailing list
///  or try  http://www.team.net/cgi-bin/majorcool
///  Archives at http://www.team.net/archive


<Prev in Thread] Current Thread [Next in Thread>
  • Minor tale of woe...., Michael D. Porter <=