[Fot] TR6 Piston / Head Clearance

Bill Babcock ponobill at gmail.com
Fri May 27 15:26:08 MDT 2016 

Indexing in this case means aligning the crankshaft in the grinding machine so that as the crank is rotated, the journal center is the center of rotation. In a four cylinder triump crank journals two and three, and journals one and four are in the same plane. So the grinder aligns the machine so 1 and 4 are concentric, grinds those two, then indexes 2 and 3, and grinds those. In a six there are three sets of concentric pairs. Any indexing error means the two journals ground with error may reach TDC at a different degree of crank rotation (offset horizontally to the main journal plane), or at a different height above the center of crank rotation (offset verticallly), or both. 
> On May 27, 2016, at 10:13 AM, TR3driver at ca.rr.com <mailto:TR3driver at ca.rr.com> wrote:
> 
> I'm a bit confused, Steve (not unusual these days). When you say "indexing", I think of rotational position; which would affect timing, but not piston/head clearance. 
> Are you saying that the length of the throws (radial position) can be off as well?
> 
> --  Randall
> 
> On 27 May 2016 10:45 a.m., Steve Yott <tr4 at wi.rr.com <mailto:tr4 at wi.rr.com>> wrote:
> Since most of you like to play the “death with pistons” game keep in mind one additional factor as you are building your engines.  Over the years I have found crankshafts which were reground and the throws were not very precisely indexed.  When a crank is setup on the grinding machine for grinding rod journals it is set and reset by the number of “throws”… on a 4 cylinder engine the grinder has to be indexed twice and on the 6 cylinder, 3 times.  If the grinder, either the person or the machine is not perfectly accurate you will see variations of TDC for the throws!  I have seen these deviations be as much as .006” when a good grinder will hold dimensions within .001”.  
>  
> So, if you are running close squishes…. Measure TDC on #1 and #2 on the four cylinder and #1, #2 and #3 on the 6 motors….. this way to can make sure your throws and TDC’s are spot on.
>  
> Steve Yott
>  
>  
> From: John Styduhar [mailto:johnstydo at gmail.com <mailto:johnstydo at gmail.com>] 
> Sent: Thursday, May 26, 2016 4:32 PM
> To: Gregmogdoc at surfnetusa.com <mailto:Gregmogdoc at surfnetusa.com>
> Cc: Charly Mitchel; Steve Yott; Jim Gray; Triumph 'Friends of Triumph
> Subject: Re: [Fot] TR6 Piston / Head Clearance
>  
> My forged pistons are .006" in the hole at TDC and I use a .030" thick solid copper head gasket and stock crank at 6200 rpm. When removing the head, the piston tops are clean in the squish area and it looks like a slight indentation at the ledge of the combustion chamber, probably from piston rock when the engine is cold.    
>  
> On Thu, May 26, 2016 at 3:23 PM, Gregmogdoc at surfnetusa.com <mailto:Gregmogdoc at surfnetusa.com> <Gregmogdoc at surfnetusa.com <mailto:Gregmogdoc at surfnetusa.com>> wrote:
> IN our experience with TR-4, and English Ford Kent
> racing engines the safe clearance between the head
> and the piston crown is .035".  A TR-4 with billet
> rods will just "touch" the head at 6800 rpm with
> .026" clearance. It will "hit" the head hard enough
> to make an imprint in the piston crown at .029"
> I would say that the TR-6 crank probably flexes more
> than a TR-4 does at high rpm. You would like to have
> a little safety margin, I would think. I would not
> run less than .035", maybe even a couple more if the
> engine is going to run over 6,000 rpm.
> 
> 
> Greg Solow
> The Engine Room
> Sports Car Specialists
> Santa Cruz, CA 95060
> 831 429-1800
> 
> 
> 
> ------- Original Message -------
> From    : Charly[mailto:charly at mitchelplumbing.com <mailto:charly at mitchelplumbing.com>]
> Sent    : 5/25/2016 6:52:35 PM
> To      : tr4 at wi.rr.com <mailto:tr4 at wi.rr.com>; toodamnfunky at comcast.net <mailto:toodamnfunky at comcast.net>
> Cc      : fot at autox.team.net <mailto:fot at autox.team.net>
> Subject : RE: Re: [Fot] TR6 Piston / Head Clearance
> 
>  I tried b u idling a TR6 motor with a pop-up on the
> piston on c e. Instead of having the pistons cut
> down to zero clearance I left them about .005" high.
> It eventually bent the rod and broken it. The
> pistons had an imprint of the combustion chamber on
> them. I learned that at 6000 rpm's, there is
> enough deflection in the crank to let them hit the head.
> I believe most head gaskets are .0035" aren't they?
> Charly Mitchel
> TR6 #44
> 
> On Wed 25/05/16 11:31 AM , toodamnfunky at comcast.net <mailto:toodamnfunky at comcast.net> sent:
> > The rattling is likely piston slap on cold forged
> pistons. Did it go
> > away when it warmed up and came back on the next
> cold start ?jim
> >
> > -------------------------
> > FROM: "Steve Yott"
> > TO: "Robert Lang" , "FOT List"
> > SENT: Wednesday, May 25, 2016 11:27:27 AM
> > SUBJECT: Re: [Fot] TR6 Piston / Head Clearance
> > I doubt that your .030 squish would cause the
> rattling as you
> > describe.  The deflection caused by the crank, rod
> and piston in order
> > to hit the head at .030 would be way up in the
> rpm’s like 8000!
> > Did the rattling go away after all the parts warmed
> up and oil was
> > well disbursed or is it still rattling?  My first
> guess would be
> > either the engine was not pre-oiled or you have
> loose piston pin
> > bushings….  Were the rods rebuilt with new bushings
> fitted to about
> > .0003?
> > Steve Yott
> > FROM: Fot [ mailto:fot-bounces at autox.team.net <mailto:fot-bounces at autox.team.net> ] ON
> BEHALF OF Robert
> > Lang
> > SENT: Wednesday, May 25, 2016 11:29 AM
> > TO: FOT List
> > SUBJECT: Re: [Fot] TR6 Piston / Head Clearance
> > Hi,
> > Where I was going with the query was this: I had a
> late block
> > "decked" with the intent of making the deck flat.
> The machinist took
> > of .032 to accomplish the goal. With a head gasket
> installed and the
> > head torqued, the clearance in the squish area is .030.
> >
> > I had initially wanted only about .025 removed, but
> we had to shave
> > an extra .007 to get rid of the fire ring cuts.
> >
> > On initial startup, the motor sounded like it might
> be "rattling" and
> > I'm trying to figure out why.
> >
> > When I used a stethescope on the block, everything
> sounds okay - no
> > rapping and the valve train sounds "normal" and
> there were no weird
> > sounds coming from the crank.
> >
> > I guess where I'm going with this is: if piston /
> head clearance is
> > too tight, I'll see some sort of indication on the
> piston, right?
> >
> > TIA for any sage advice.
> >
> > This is my first experience "decking" a block. I'd
> like to get it
> > right, I don't have the resources to start a new
> block from scratch.
> >
> > Regards,
> >
> > Bob Lang
> > _______________________________________________
> > fot at autox.team.net <mailto:fot at autox.team.net>
> >
> >  http://www.fot-racing.com <http://www.fot-racing.com/>
> >
> > Donate:  http://www.team.net/donate.html <http://www.team.net/donate.html>
> > Archive:  http://www.team.net/archive <http://www.team.net/archive>
> > Forums:  http://www.team.net/forums <http://www.team.net/forums>
> > Unsubscribe/Manage:
> >
> http://autox.team.net/mailman/options/fot/toodamnfunky@comcast.net <http://autox.team.net/mailman/options/fot/toodamnfunky@comcast.net>
> 
> >
> >
> 
> _______________________________________________
> fot at autox.team.net <mailto:fot at autox.team.net>
> 
>  http://www.fot-racing.com <http://www.fot-racing.com/>
> 
> Donate:  http://www.team.net/donate.html <http://www.team.net/donate.html>
> Archive:  http://www.team.net/archive <http://www.team.net/archive>
> Forums:  http://www.team.net/forums <http://www.team.net/forums>
> Unsubscribe/Manage:
> http://autox.team.net/mailman/options/fot/gregmogdoc@surfnetusa.com <http://autox.team.net/mailman/options/fot/gregmogdoc@surfnetusa.com>
> 
> 
> 
> 
> 
> _______________________________________________
> fot at autox.team.net <mailto:fot at autox.team.net>
> 
> http://www.fot-racing.com <http://www.fot-racing.com/>
> 
> Donate: http://www.team.net/donate.html <http://www.team.net/donate.html>
> Archive: http://www.team.net/archive <http://www.team.net/archive>
> Forums: http://www.team.net/forums <http://www.team.net/forums>
> Unsubscribe/Manage: http://autox.team.net/mailman/options/fot/johnstydo@gmail.com <http://autox.team.net/mailman/options/fot/johnstydo@gmail.com>
> 
>  
> _______________________________________________
> fot at autox.team.net <mailto:fot at autox.team.net>
> 
> http://www.fot-racing.com <http://www.fot-racing.com/>
> 
> Donate: http://www.team.net/donate.html <http://www.team.net/donate.html>
> Archive: http://www.team.net/archive <http://www.team.net/archive>
> Forums: http://www.team.net/forums <http://www.team.net/forums>
> Unsubscribe/Manage: http://autox.team.net/mailman/options/fot/bill@ponostyle.com <http://autox.team.net/mailman/options/fot/bill@ponostyle.com>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/fot/attachments/20160527/f1a54d67/attachment-0001.htm>

More information about the Fot mailing list