[TR] Advice on high compression head

DAVE HOGYE dlhogye at comcast.net
Wed Apr 7 17:09:57 MDT 2021


Greg made an excellent suggestion.  You can relieve or bevel the edge next to the squish area a lot, if it isn't already.  Basically back to the factory shape before the milling and then some.  
I took .125" off my head for racing and got around 10.8 compression after chamber work, and my car will run on 91 pump gas after retarding the timing 2 degrees.  I mix pump gas and race fuel 50:50 when on track.  I keep race gas at home and a gallon or two mixed with pump gas settles any concern about detonation with no retarding of the timing for street.
You can see my head work on my restoration and race car build Youtube video, starting around 7:50 in the video.
https://www.youtube.com/watch?v=UW-cSGzyKXs&t=3s
Dave H. 

>     On 04/07/2021 3:39 PM Greg Lemon <grglmn at gmail.com> wrote:
>      
>      
>     If you want to save the head you may be able to lower the compression ratio a bit by reshaping the combustion chamber.  This is theoretically, I don't know how much can be removed, Kastner book would be a starting point, but you would probably want to take out more than that, measure combustion chamber size, etc.
> 
>     On Wed, Apr 7, 2021, 5:23 PM Dave Connitt < dconnitt at fuse.net mailto:dconnitt at fuse.net > wrote:
> 
>         > >         Hi Cliff,
> >         A lot of racers have milled the heads of wet liner engines to increase compression. In Kas Kastner’s TR4/TR4A competition preparation manual, he goes into much detail about how to reshape the combustion chambers in the head to reduce/eliminate “hot spots”. This may be the cause of your pre-ignition. Yoy may want to get that book and read over his cylinder head chapter. Regarding the push rod length, the length reduction is directly related to how much material is removed from the head so just buying shortened pushrods won’t get you the best results. I think you should figure out how much material was removed from the “stock” head and shorten the pushrods accordingly. 
> >         I think you can certainly save the head but you will need to do some homework reading over Kas’s competition prep manual and find a good automotive machinist for the pushrods.
> >         Dave Connitt 
> > 
> >         Sent from my iPhone
> > 
> > 
> >             > > > On Apr 7, 2021, at 5:41 PM, DAVID MASSEY < dave1massey at cs.com mailto:dave1massey at cs.com > wrote:
> > > 
> > > 
> > >         > > 
> >             > > >             I went the band-aid route on my TR3 for the same reason.  But the right way is to get a machinist to shorten the pushrods.  BPNW sells short rods for the TR6/SC engine but at that time they didn't have any for the wet-sleeve engine.
> > >              
> > >             Dave
> > > 
> > >              
> > >              
> > >             -----Original Message-----
> > >             From: Cliff Hansen <cliff_hansen at outlook.com mailto:cliff_hansen at outlook.com >
> > >             To: list Triumph <triumphs at autox.team.net mailto:triumphs at autox.team.net >
> > >             Sent: Wed, Apr 7, 2021 4:23 pm
> > >             Subject: [TR] Advice on high compression head
> > > 
> > >             The telenovela “What’s going on with this 4A cylinder head” has developed a new plot twist.
> > >              
> > >             The head, after cleanup, measures 3.21” from bottom to the surface for the valve cover gasket. Stock is 3.330 (if I got the number correctly). Some PO cut 0.11 off, because only 0.010” was removed in this round of clean up. Now I can see an explanation for the persistent pinging I’ve dealt with over the last few years (head has been milled so compression is high, material near intake valves has been thinned, increasing likelihood of hot spots – I’m getting this from Kastner’s preparation book), which I had thought was due to leaking intakes, carb shafts, or operating at higher altitude.
> > >              
> > >             As is, I can’t use this head because there is not enough slack in the valve train to give 0.010” clearance on several valves. I didn’t notice before, but now that I am looking, all the valve adjusters were nearly backed out all the way.
> > >              
> > >             Looking for advice from the list: is there any reasonable way to use this head?
> > >             - I’d prefer to reduce compression but don’t see any reasonable way to accomplish that. I called GasketWorks and he gently discouraged me from getting a custom thick head gasket, saying instead I’d be better off finding a head which had not been milled so much.
> > >              - Shimming the rocker pedestals to get valve clearance feels like a bandaid which certainly won’t address the pinging (assuming that the pinging is a result of the shortened head).
> > >              
> > >             Would appreciate any advice on the way forward.
> > >              
> > >             Cliff
> > >              
> > >             Sent from Mail https://go.microsoft.com/fwlink/?LinkId=550986 for Windows 10
> > >              
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