[TR] Advice on high compression head

[Jerry Van Vlack]

Cliff

Here is my experience with a milled TR4A head. After a couple of millings of the head I ended up somewhere around .110 off the head. I had 2 Head Gasket failures one caused by me using the wrong “modern” head gasket from Cometic and the second because I failed to re-torque the head using an original Payen AE 330 head gasket. However I never had pinging issues using the current 93 octane premium fuel. The key here is to limit the amount of total timing advance to match the available fuel. I have a friend who had a similar amount milled from his head and didn’t have any head gasket issues with the Cometic modern gasket. He drove his car much more aggressively than me as well. Can’t explain why.
It’s also very important that whichever gasket you use, the gasket does not protrude into the combustion chamber.  It turned out the Cometic I used did and that’s where it failed.

>From previous email with you I learned you are using the copper reproduction Payen 330 head gasket with 86mm liners. In my case I had 87mm liners. That should work but be certain to re-torque the head after a few heat cycles. (I’ve done that now with the latest install and so far all is good) I must also say I have replaced the .110 head with one milled only .075 and don’t really notice much power loss over the .110 head. It’s noted that the Kastner Comp manual only recommends .090 for a street engine. I changed heads because most summers I, along with several friends take long trips covering several thousand miles and I didn’t want a head gasket failure miles from home. However; I do carry a spare head gasket and the tools to change it with me. Good insurance as no failures now after close to 6000 miles. Previous to me messing with that original milled head at .090 I drove the car for 30+ years and many thousands of miles without a failure using a Payen AE330 head gasket.

You can make that head work but retard the timing (I run 28 degrees total advance) you may need to back it off to less than 28 degrees. Re-torque the head more than once.

As for the push rod / valve adjustment issue. Call Ted at TSI and have him make a set of pushrods shortened by the amount removed from the head and you’ll have your adjustment issues solved.

Hope this helps.

JVV

From: Cliff Hansen 
Sent: Wednesday, April 7, 2021 5:23 PM
To: list Triumph 
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 for Windows 10

 



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