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Triumph TR6 - TR6 Hi-Performance Street Cam

I have torn down my spare '74 TR6 engine and after close inspection of the condition of the innards I will be doing a major rebuild. The cam is toast! What I won't be replacing are the crank, pistons, con rods, rockers and shaft. Everything else will be new - rings, mains, oil pump and all the other related bits like bushes, oil seals, thrust washers, etc., etc. Question: has anybody installed the "Goodparts" GP2 cam? (listed by TRF and of course by Goodparts) I have budgeted for the GP2 cam with the following related parts from Goodparts - uprated tappet set, bronze valve guides and teflon seals, uprated valve spring set. Also looking at a full set of hardened valves from Moss. If anybody has done this cam installation I would appreciate some comments. Also, if anybody has installed the GP2 cam, do you believe the parts I have selected are the best choice for the application. Any tips or advice would be greatly appreciated. I cannot budget for the roller rocker set, alloy flywheel, etc. as I cannot afford another mortgage. Thanks.

1976 - TR6
Bob Evans

Do you also plan to install cam bearings? Richard Good says that with the GP2, cam bearings are probably not needed, but are with the GP3. Just curious is the bearings are worth the effort or would that just be added cost w/o much benefit.

I have not done what you've described, but I've discussed doing this very modification to my 71 engine with Richard Good. I have an email from him suggesting what all needed to be done along with installng the cam. Were I you, I'd write Richard a note, tell him your plans and seek his counsel as to what's best. He did very much recommend hid rocker roller mod, so I'm seeking bids on my first born to establish the budget for all that!!

Please keep us informed on how your MOD proceeds.
Doug Baker


Regarding cam bearing, I read an interesting rebuild article in one of the club groups. Might have been the Georgia Triumph club. The article outlined that as you increase in the performance levels of cam shafts the need for cam bearings increases. This is due to the increasing load that is applied downward onto the cam and then this load transfered to the block.

As you increae in performance of the cam, this typically means larger lobes and faster lift. This of course means the valves will be open longer than the stock cam origionally allowed. But in order to allow the valves to close quickly, and reduce valve float, many times a stiffer spring is needed. This stiffer spring means more force to open the valve, which transfers to the rocker, then the pushrod, lifter to the cam, then the force to the block. Kind of like the dog, that ate the cat, that ate the mouse, that ate the fly, in the TR house that Jack built.

And then you mentioned changing rockers? Increased ratio means, well you get the picture....

My 2 cents, if you are doing a motor for performance, any rebuild should include first off, a line bore of the mains. If you speak to many of the old TR experts (for eg, Ted Schumaker of TSImports) they all say the mains can be really off right from the factory. Then while that is getting done, go for the cam bearings. If you are doing a stock rebuild for tiddling around town, then probably not needed.

I've the GP2 and most everything else you mentioned. Also a set of 1.55 RR's. The idea was to take it to the limit without cam bearings - it's been quite successful so far. You'll be pleased with the new camshaft.

Some say don't use valve seals - but they work fine, especially if you have an external oil feed line.

Brent B

Thanks Guys. I had hoped to avoid line boring for cam bearings and likewise for mains. The block is low mileage with no apparent damage or noticeable wear, so honing and a dip should take care of the prep work. With the GP2 cam I am looking for a little "jump" in the TR6, not a large power gain. I intend to upgrade with all the GP2 related bits I previously mentioned but will stop short of the roller rocker setup as it's too pricey. As it is, I'm looking at $1000 USD for parts - enough for now. I'll also be losing all the smog crap to let her breathe again, which is not illegal to do here (yet). Down the road a free flow exhaust is planned so an overall horsepower gain of 15 - 20 over stock would be quite satisfactory. Any other comments would be welcome.

1976 - TR6
Bob Evans

Bob--The only thing missing from your list is increasing the 1976 compression ratio from 7.5:1 to a respectable 9.5:1. This head shave will run you at most a few hundred bucks, but the performance return is the greatest of all the improvements you've listed.

Rick O.
72 TR6
9.5:1 CR
Kent Z-19 cam
Rick Orthen

kj [ajax] and all

Watch the line boring thing VERY carefully; you can EASILY get into problems at the rear main oil seal. If the crank bore is out of true, the line bore must be done to the greatest amount of divergence, which then could leave the crankshaft not quite centered in the seal as much as nature intended, or BLMC either for that matter.

Think this one out Bob.

Luck all.


Thanks Guys:

Thanks for all the very helpful advice. The great thing about this forum is the ability to learn from others and the expertise out there is truly amazing. I held off on my comments til now, hoping for a few more replies. I'm nixing the line boring on this build as the engine is very low mileage and there is little or no wear apparent. The pistons, cylinder walls and cam seats all look very good and the crank is in great shape - even the thrust washers looked pretty good. What happened was one of the frost plugs got two rust pinholes and water from the waterpump got routed into the sump - very messy and only apparent when it was all torn down. Remember, this is a used '74 engine I picked up for $200 complete with carbs, intake & exhaust manifolds and starting motor, distributor, etc. As I stated on another thread, I'm rebuiling this one with a few mild modifications but the original '76 engine will over time, a long time, get the full treatment with GP2 cam, lightened flywheel, roller rockers, hardened valves and seats and all the related bits and the downdraft Webers, etc. For now, I'll get a new engine with a little added zip for a reasonable cost and still be close to stock specs. I wonder when Moss will finally release their proposed TR6 supercharger. THAT should be a popular add-on for all of us 6 owners. I wonder if they offer financing too?

Bob Evans

I did not chime in previously as I thought the ground had pretty much been covered, but feel that I must now. If you pass on bumping up the compression ratio, then much of your effort will go to waste. While compression is not the be all, end all of where it's at, it takes you far down that path. But sticking with that low 7.5:1 compression ratio is defintely not where it's at.

Rick is on target, carefully calculate your swept cylinder volume, the unswept cylinder volume (including the gasket space) and then "cc" each combustion chamber on the head. Equalize them as required and then determine how much to shave the head to get where you want. I recommend shooting for something in the 9.25 to 9.5:1 compression ratio. There are lots of books and I dare say in this day and age, lots of websites that tell you how to do all of this.

Read up and do it right. Unless you are paying someone to do it all (measuring, calculating, etc.), you will mostly spend your time, the only money is for the actual machine work itself that way.

Thanks Steve. Sounds like very good advice on the compression upgrade.

Bob Evans

I agree with Steve, I took off .1 inches off a 76 engine and the the diference was dramatic. I with I had put in a cam because it ran out of breath above 3.5K rpms.

This thread was discussed between 05/02/2006 and 21/02/2006

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