[TR] Advice on high compression head

[Greg Lemon]

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> 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> 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>
> To: list Triumph <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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