Vixen 2500 Camshaft

[GJL]

I was doing some work on my car and have discovered that the front cam lobe (valve no1, exhaust) was excessively worn. I was looking into different cam characteristics and would be interested in any input from those running a 2500 engine.
The car is running twin SU 1.75 inch carbs. Had a full rebuild some years ago. Converted to unleaded head.
The car seemed to come into the power band at about 3250rpm and I was assuming the cam fitted during the rebuild was quite a hot cam. The history file showed invoices for a "Sports R" 6 cyl camshaft which I assumed might be a Kent cam but couldn't find out any more.
Today I have removed the cam and it is a Kent TH5, which according to the Kent specs should be in the powerband at 2200 to 7000, but I felt it was a narrower band and in the higher rev range. Perhaps this could be due to wear in the cam as other lobes were worn.
I had decided a calmer cam would suit, I didn't want to thrash the nuts off the car and rather than pretending I have racing driver skills and credentials, I want something with a bit of go and also power on tap when I drop a gear to overtake a transit. With this in mind I had narrowed my ideas down to:

KENT

TH12
Engine 2.5
Description High Torque
Power Band 1500-6500
Specifications
Cam Lift (mm) 7.29mm Inlet/Exhauust
Duration 270° Inlet/Exhaust
Full Lift Inlet 104° ATDC
LTDC 2.28mm Inlet
Timing 31/59 67/23
Valve Lift (mm) 10.66mm Inlet/ 10.61mm Exhaust
VC (mm) 0.41mm Inlet/ 0.46mm Exhaust

OR

Part No. TH5-6
Manufacturer Triumph
Engine 2.5
Description Fast Road
Power Band 2200-7000
Specifications
Cam Lift (mm) 7.44mm Inlet/Exhaust
Duration 280 Deg Inlet/Exhaust
Full Lift Inlet 103 Deg ATDC
LTDC 2.84mm Inlet
Timing 37/63 73/27
Valve Lift (mm) 10.74mm Inlet/ 10.69mm Exhaust
VC (mm) 0.56mm Inlet/ 0.61mm Exhaust
(which is what was fitted but the figures don't seem to match the reality I found in driving the car so I am thinking either I disregard this one or that the spec has altered over the years since the rebuild, I will ring Kent to confirm).

OR

REVINGTON TR
TR250, 5, 6 Sprint Cam New with inlet timing 37°-73° and exhaust timing 73°-37° giving 290° overlap.

With a cam lift of 0.264" this cam produces up to 146 BHP at the rear wheels although this figure depends hugely on the cubic capacity of the engine and the quality of the engine build.

OR

NEWMAN CAMSHAFTS
Phase 2 Camshaft (see image for spec)


If anyone has any input it would be greatly appreciated.

Many thanks

[GJL]

Just to add, lobes 7 and 8 are also worn, but not as much as lobe 1.
Lobe 1 cam follower looks OK but cam followers for 7 and 8 are concave and show definite signs of wear.
I think the uprated valve springs might have attributed to wear so I think I will fit standard valve springs but upgraded cam followers.

Any input welcome.

[TVR by BVR]

When you fit your new cam fit also new cam followers, assemble all with a assembly lube, use a running-in oil for the first 500 miles, after that makes sure you are using a high zinc engine oil.

The reason why the lubes are worn is the lack of zinc, don't use synthetic but use a Penrite HPR Classic 20W60 or something equivalent.

[GJL]

Thanks, I will look into the Penrite oil, it might help extend the life this time round.
I was planning on all new followers anyway, hardened and lapped.
I have camlube or assembly lube on my shopping list too.
I try to use the car a couple of times a week, but I know the previous owner had the car for about 15 years and didn't use the car very much, so oil will have drained down and perhaps this has not helped either.

[Mercdriver]

I had a 2500M fitted with triumph TR250 engine, geriatric to say least as to an American spec.

I rebuilt the engine, rebore, new pistons, bearings etc but found it disappointing. Looked at TR6 engine and noticed a web on cylinder head that was much thicker on TR250 engine. Sorry cannot remember which side it was on but near front. Changed carbs to twin SU’s.

Used a flycutter to skim the head to same dimensions as TR6, cannot remember how much I took off but it was about 2mm. Fitted fast road cam and wow transformed the car.

Local triumph specialist reckoned it was giving about 170BH!

[GJL]

Thanks Mercdriver. Can you remember which spec the camshaft was? There are a few listed as fast road types and was trying to decide which to go for. What kind of RPM did you find it came into power? It's just that my existing one is a Kent TH5 and according to the waffle it should be in the powerband at 2200RPM upwards but I found it more like 3250 or 3500.
My car had an extensive rebuild with +.020 pistons, a TR6 head converted to unleaded. It has twin SUs and it did seem to have plenty of power but with the camshaft lobes a bit worn it obviously wasn't at its optimum. I also have a programmable 123 distributor which can be controlled from my phone so I had tweaked it to get the best results for my set up.

[Mercdriver]

. Can you remember which spec the camshaft was?

[/quote]

Sorry this was in the early 90’s, cannot remember, think it was described as a fast road cam. It might have been a Kent cam. I think I fitted an adjustable gear so that the timing could be adjusted to a finer degree.

by Fitting a tr6 head and su carburettors you achieved the same result as I did only I did it on the cheap by flycutting the head down to increase compression ratio. What about the needle and jets in the carbs? Could you increase fuel flow by changing them.

When I asked local guy what HP I was getting as the fuel injected engine achieved 150bhp on 2.5 litres which was good at that time, not that good now but it was back then. He thought about 170 certainly was a quick car on sticky toyos

[GJL]

Thanks Mercdriver. A number of years ago a previous owner spent about £6000 on engine upgrade works so the car is quite lively. I just wanted to make the right choice so I can fit and forget for a few years.

[TrumpyM]

My 2500M is fitted with a Piper 777/1 cam - this was a custom profile produced for Racetorations. I don't think that they are available anymore!

Anyway, it is a high torque cam (Timing 28-60,60-28, Lift 0.450" & 0.448", Duration 268, Full Lift 106) and I am quite happy with it. The closest one that you have identified is the Kent TH12.

I am running triple Dellorto 40's with a 'big valve', gas flowed head and a lightened flywheel so my setup is somewhat different to yours.

There are a few things to take into account when making your decision:

1) Are you really ever going to rev the long-stroke engine over 6,000 rpm? Personally I wouldn't without plenty of expensive bottom end/piston work!
2)As Mercdriver correctly mentioned, you have probably got a low compression federal spec CF engine so the advertised power gains are unlikely to be achieved with a fast road cam anyway.
3) Be careful with fitting standard valve springs with a modified cam - it might require uprated springs - to be sure seek the advice of the supplier.
4)Are you sure that you problem isn't elsewhere? It seems strange that your powerband is so high up and narrow. Did you check your cam timing, ignition timing and your carb jetting? I also had a Kent TH2-6 and found the engine quite tolerent of both that and my current cam.
5) Consider how you will be driving your car - for normal road use with a few spirited blasts I would think that a high torque cam would be the most suitable. If you are going to mainly use it for sprints/racing then perhaps a race cam would be more suitable.

Have fun!

Vince

[Dinlowgoon]

The standard 150BHP TR6 cam is pretty lumpy, try and find a new billet one.

[Mercdriver]

How many miles has it done since major rebuild by previous owner? If I spent 6K on an engine I would not expect it to wear out the camshafts lobes as bad as you describe.

[GJL]

Yes, I agree, although the car was used infrequently for a number of years which is never good for an engine.
I spoke to a couple of camshaft suppliers and it could be the uprated valve springs that accelerated the wear. I suppose it could be a shaft from a bad batch or poor quality cam followers. It is unlikely, but might even be possible that the original cam followers were used again.
I am left pondering whether to use uprated valve springs with a fast road cam, standard springs and a fast road cam or high torque cam with standard springs.
Newman offer upgraded cam followers which have also been lapped which should minimize wear.

[LLantrisant]

such wear is usually expected with high mileage and in some engines in combination with lack of maintenance...with collector cars, low anual mileage, even with the wrong oil (missing zinc) such a defect should not come-up.

in your case its definately a problem from Kentcams...they have had massive problems in the past with the quality of their cams (hardening)...i have had 2 damaged (ford)engines, due to wear of cam-lobes and the particles in the oil-circuit.

even they may have solved all those issues iand have increased their quality, for me Kentcams is meanhwile a no-go.

[GJL]

LLantrisant, thank you.
Yes I wondered about this. The car has always been maintained and had regular oil changes and is warmed up gently.

I am tempted to use Newman as they have had some favourable comments on the TR6 forums. I spoke to someone there last week (as well as Kent and Revington TR) and they seemed helpful and it sounds like their cam followers are of good quality too. If anyone has any positive or negative experience with Newman it would be good to hear.

[StewB_v6]

I think the drain down factor is most likely a heavy contributor which will be exacerbated by heavy duty valve springs. Rover V8s are famed for their ability to make cam lobes dissappear & sparingly used versions in TVRs & the like are amongst the worst afflicted. It's amazing how quickly things wear as soon as the surfaces scuff up.

I know nothing specific relating to cam specs for the Triumph engine but many have made sound points. It would seem that the 150bhp TR cam would be a good starting point as you'd have decent idle quality & know that the matching springs + followers would work to give the correct valvetrain geometry. I've had issues with some aftermarket cams having insufficient quietening ramps as there is generally a compromise if regrinding an existing core. Decent zinc rich oil & making sure you have oil pressure (and hence oil flooded over the splash fed surfaces) before starting following standing should help it last too. It's certainly worth checking the compression ratio & maximising that as you'll gain all the way through the range & by using a half decent ignition system you can run correct timing without running into det.

Stew.

[Mercdriver]

An uncle of mine had a P6 Rover with V8 engine. He ran the main bearings in it.

He had a very short steep drive in front of garage and he used to park nose down, the pick up point is at the rear he got told so he was starving the engine of oil every time he started it up.

Engine rebuilt and parked in the street!

Edited by Mercdriver on Thursday 12th August 18:02

Edited cos the pick up point must be at the rear of the engine to starve the bearings, oops!

Edited by Mercdriver on Friday 13th August 22:49

[GJL]

Thanks to everyone for the input so far. I like to do as much research as possible and other peoples advice and experience can be invaluable. Anyone else please feel free to chip in with any ideas or pearls of wisdom.