GT6 MK3 (Aug1973) Recommendations For Head Work Needed.

[TrafficMan]

When I acquired my car it was missing its engine apart from all ancillaries.    I acquired a NOS Short Engine - Part No. UKC559 (domed top pistons) from TD. Fitchett along with a "bare" cylinder head to suit.  I'm now seeking recommendations for having the head prepared for use.  I'm thinking along the line of having an unleaded conversion and maybe polished and ported whilst I'm at it.  I will also need all rockers, valves, rods etc.  Should I source and pass on these items separately or find an individual/firm who can do the whole job ?.  For information - the only other upgrade I may go for is a "fast road" camshaft, when I source that.  Wont be doing any track days as wanting to keep her fairly standard.    I am Nottingham based.    Any help/suggestions much appreciated.   Thanks   Paul   

Short Block Illustrated For Info -

 

[Clive]

Is the cylinder head brand new? 

But you shoudl be able to source good spares, though you will need to do your research. Bear in mind if you supply all the bits, the builder will not warrant any of them. 

So maybe have a word with Chris Witor, he tends to only sell good stuff, and will be able to offer advice. As to cam, something like a mk2 GT6 cam is a very good all rounder. Chris does a special cam based on that, again he can advise. 

[thescrapman]

Is there any clue as to what cam is fitted to the short engine?

ISTR the Fitchett engines are very late 2000 saloon engines, so may have a cam of a less sporty nature, which won’t suit the GT6 really.

It will need a GT6 cam and you will also need to raise compression a bit I suspect, which will be skimming head as it is domed pistons.

As it is a new bare head, may as well get seats fitted as there won’t be any lead memory. 

What size valves does the head take? There are a few variations.

 

 

[TrafficMan]

3 minutes ago, clive said:

Is the cylinder head brand new? 

But you shoudl be able to source good spares, though you will need to do your research. Bear in mind if you supply all the bits, the builder will not warrant any of them. 

So maybe have a word with Chris Witor, he tends to only sell good stuff, and will be able to offer advice. As to cam, something like a mk2 GT6 cam is a very good all rounder. Chris does a special cam based on that, again he can advise. 

Yes, brand new, old stock.   Thank you for the CW recommendation.  

[TrafficMan]

4 minutes ago, thescrapman said:

Is there any clue as to what cam is fitted to the short engine?

ISTR the Fitchett engines are very late 2000 saloon engines, so may have a cam of a less sporty nature, which won’t suit the GT6 really.

It will need a GT6 cam and you will also need to raise compression a bit I suspect, which will be skimming head as it is domed pistons.

As it is a new bare head, may as well get seats fitted as there won’t be any lead memory. 

What size valves does the head take? There are a few variations.

 

 

The new short engine does not come with a camshaft.  The part number stamped on the short engine is listed in the MK3 GT6 Parts Book so I believe it is the correct engine. That's certainly how I purchased it.  I will measure the original valve sizes.

[Iain T]

I used CTM Performance at Dagenham Essex. A long way from you but they are good and have done loads of 6 pot Triumphs. 

Iain

[Ian Foster]

+1 for CTM (Charlie Mahoney).

He actually built me a modified TR6 head as my original GT6 head was cracked between the valve seats (not unusual). He built it with new valves (Cosworth s/s), springs (Swedish wire) and bronze valve guides with valve stem oil seals. 

The standard cam for a Mk2 GT6/Vitesse is a 308788 generally thought to be the best standard cam for carbs. I actually have a Chris Witor CW3021, which is the 308788 profile but ground to give an addition 0.030" lift on the inlets (IRRC).  https://www.chriswitor.com/products.php?cat=254&sortby=4

Rimmers offer new rocker shaft with close tolerance bronze bushed rockers, which would be a good option if you are starting from scratch. I bought one to replace my 210k miles original rockers.

Ian

 

[Iain T]

23 minutes ago, Ian Foster said:

Rimmers offer new rocker shaft with close tolerance bronze bushed rockers, which would be a good option if you are starting from scratch. I bought one to replace my 210k miles original rockers.

I bought the bushed rockers and shaft and gave them to Charlie who reamed the bushes to fit the actual shaft. That way I know they were correctly matched to fine tolerance and not taking the word of a reseller. 

Downside is due to the head breathing much better you will probably have to play with needles as the standard 6AC get very lean over 3500rpm. Been there! 

Iain 

[daverclasper]

On 07/01/2023 at 12:41, Iain T said:

That way I know they were correctly matched to fine tolerance and not taking the word of a reseller. 

Iv'e not checked the manual, though I had an idea it was quite a loose fit?.

[Iain T]

36 minutes ago, daverclasper said:

Iv'e not checked the manual, though I had an idea it was quite a loose fit?.

No I think the diameter clearance between the rocker bush and shaft is only around 1.5 thou. Just enough to squeeze some oil out. 

I bought a 'new' unbushed rocker set and found the clearances way too big and oil pi***d out and made an 'ell of a clatter. Returned it and bought separate bushed rockers and shaft but you do have to get them reamed to suit. 

Iain 

[Ian Foster]

Checking my files, I actually bought my rocker set from Moss Europe. They were offering a discount at the time and are a 'honed to fit' set.

Rockers Arms & Rocker Shaft Kit - TR5-6

The standard rocker arms were never bushed, and the tolerances specified are based to the cast iron on steel interface. This translates to a clearance of 0.0028" to 0.0033". If your rockers are worn, both the rockers and the rocker shaft must be replaced. If the bore diameter in the new rocker is on the high side, and your rocker shaft is on the small side of the tolerance, the clearance will be close to the maximum allowed. In addition, the standard components will wear more quickly than rocker arms fitted with bushings. We have arranged for bushed rocker arms to be made for us by a specialist supplier here in the UK. The rockers are identical to the OE rocker in shape, but they are sized for and fitted with a bronze bushing. They must be matched to a specific rocker shaft by honing the bushings.

The advantages are numerous. With bushings honed to fit, the rocker arms and the rocker shaft will last longer. With the tighter tolerances, you will not lose as much oil pressure as you would with the standard un-bushed rocker arms. The other critical area for wear is the tip, which comes in contact with the valve stem. The tips are very hard, 50-52HRC (Rockwell C scale), which is the same as new unused rocker arms. Our kit offers matched sets of rocker arms and rocker shafts, with the bushings already honed to give a clearance of 0.002". This kit should be used with existing rocker pedestals and can be used with our solid rocker spacer kit.

https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/engine/engines-components/rockers-arms-rocker-shaft-kit-214559xktr-gp.html

With one of their % off deals it was cheaper than buying the parts separately and then reaming/honing.

Has made quite a difference to valve train noise.

Ian