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TR6 TR6 engine "freshening"

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AltaKnight

AltaKnight

Jedi Knight
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TR6 engine "freshening"

Like several others here I am doing an engine freshening on my 73 TR6 that has 54,000 miles on it; I've already done the rings and bearings prior.
I've got a new mild performance cam; it's the BPNW performance cam (290 duration, intake/exhaust 396 lift) supposed to give 12-15 HP extra. I've purchased new (hard) lifters and shorter pushrods.
I'm going to raise the compression while the head is off; BPNW advised an 80 thou (2mm) skim on the head; they say that will give 8.8:1 which is as much as they advise for street use with this cam.
Questions....
1) Are stock valve springs ok with the extra lift; or do I need the double springs?
2) The valves (indeed the whole valve train) appear in good shape; should I consider getting them changesd while the head machining is going on?
3) Any comments on the 80 thou milling number?

Appreciate the help.
 
Re: TR6 engine "freshening"

Graham,

You are very near to what I'm doing. I have the TH5 cam from BPNW, which is what i think that you are describing.

I spoke to Greg and he said that my planned 9.5 to 1 compression would be fine with the TH5. The only way to really know what you have for compression is to CC the head, both before and after shaving. The first is most important to tell how much to shave off. You don't know for sure what you are starting with, unless you do this properly.

If you have a 74 you will have double springs. I'm still waiting to see how my machinist will handle the new BPNW dual springs and removal of the bottom collar, so you need another few days before I have that answer.

While you have the head off, install new guides and valve seals. Now is the time.

If you don't do a valve job now and switch to stainless exhaust valves and new seats, you will be sorry.

Give a copy of this chart to your machine shop when you take in the head. It's all here:

https://www.goodparts.com/tech_docs/TR6_Compression_Ratio.html

Good luck,
 
Re: TR6 engine "freshening"

Graham,

I think with that that radical of a cam (290 is pretty stout cam for a little 2.5l), you could stand to go at least 9.5:1 on your CR since you'll lose a little due to overlap. I doubt very much that you'd have any valve clearance problems, but as Paul suggested, I'd go ahead with the valve job.. easier to do now than later.
 
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