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MG Midget and Sprite Technical - Kent TH2 camshaft

Hi all,

Has anyone heard of this camshaft being used in a 1500?

Just brought my first 1500 and after rebuilding the engine I noticed it wasn't running right and on closer inspection found that the number 1 inlet lobe is worn and hardly lifting the valve, I need to replace the cam but the figures don't seem to be be suitable for a fast road engine, would a TH5 be better?

Thanks for the help in advance

Ben
BR Moulson

Would also recommend that you look at the piper cams as well - especially for a 1500 (www.pipercams.co.uk)
rachmacb

The Kent TH2 is a symmetric 39-76, 295 degree duration cam with 0.382" valve lift.

As such it will NOT work well in a 1500 with a stock bottom end because it has:

a. Too much duration (for a road going 1500 I don't advise more than 280 degrees).

b. Way too much overlap 9because of the symmetric timing).

This means you move the power band upwards and the engine becomes awfully 'cammy', whilst not producing much grunt (because the 1500 will not rev).

If you are not going for a decent extractor exhaust, porting and bigger exhaust valves then the best cam to use is the Spitfire MkIII profile with 25-65 symmetric timing, 270 degrees duration and 0.340" valve lift.

I advise you go for a 'small bearing journal' type and fit camshaft bearings to the block.


The TH5 is an asymmetric 37-63 / 73-27 cam with 280 degrees duration and 0.423" valve lift.

The TH5 is a good cam in the 1500 but requires better breathing than the stock set up.


Be advised, NO ONE, at the moment can guarantee the case hardening after regrinding Triumph cams, especially not Kent (nor Moss who use Kent).
Deborah Evans

Hi Deborah

Why not opt for billet cams? We gave up on repros whenever we could buy billets about 10 years ago due to lack of case hardening. I also thought Bastuck had his cams done at Kent but I havent chatted to him for a few years.?

Peter
P Burgess

Thanks for the comments,

The previous owner had spent some money on the car already but I don't thimk in all the right places, it's now running on K&N filters with stub stacks stock twin HS4 carbs, ported head with stock valves (I can't see any mention in all the paperwork of big valves being fitted), bored +40 thou not decked, tubular manifold with straight through exhaust and the TH2 cam, runs CR 9.25:1.

I brought the car with the head off, the previous owner said the head had blown between 1 and 2 but with the cam worn on 1 then I think it would be that rather than the gasket.

Time to spend some more money!
BR Moulson

Deborah

Got my mail?
Onno Könemann

Onno, just found it in my spam folder - sorry!

Will reply tomorrow.
Deborah Evans

Hi Peter,

Unfortunately the Kent Triumph profiles are all regrinds, as I found to my cost last year when a Kent regrind lost 2 lobes within 300 miles and trashed the customer's bottom end - leaving me well out of pocket!

I believe the Pipers are regrinds too.

AFAIK the Bastuck cams are new cold-chilled iron cams made in Germany. While they do the Kent profiles, they are certainly not made by Kent. The only TH profile I have any time for is the TH5 - the rest just do not work well in the Triumph motor.

Bastuck cams are what I usually recommend for the Triumph 4-pot (to date I have never had an issue with a Bastuck cam), although I am currently talking to Newman for the supply of new billet cams - I have a couple of profiles I developed when Sprinting/Hillclimbing 1500 Spitfires (many moons ago), which I believe would work well for a 'Fast Road' set up - I ran my Hillclimb/Sprint car as my only road car for a number of years and it was a monster. :D



BR,

If you overbore a 1500 more than 20 thou then you WILL eventually end up with detonation and / or head gasket problems because of the recessed bores.

I'd deck the block, trial build, then deck the pistons, and use the early 1300 head gasket.

You can run a TH5 on stock valves but you will loose out over engines with bigger exhaust valves. I'd also up the Static CR to around 10 - 10.5 : 1.
Deborah Evans

Hi Deborah we supplied a billet Piper cam a year or so ago. I havent checked lately but will make enquiries and get back.

Peter
P Burgess

http://www.pipercams.co.uk/pipercams/www/product.php?pid=TRBP270

link to Piper mentioning billet and repro so I guess they still do billets.

Peter
P Burgess

Thanks for all the information.

Deborah you said that I would loose out without bigger exhaust valves, would it not make much sense/difference fitting bigger inlet valves as well (price aside)?

I read on another post about the compression ratio for a TH5 type cam so will definately sort that, as seen as the engines going to be taken to do the deck and have all the head off would there be anything else that you would recommend/look out for whilst its apart (fast road/hill climb in mind)?

Ben
BR Moulson

Hi Ben

We subscribe to the theory of getting the gas in then letting it sort itself out.....naturally aspirated we run as large an inlet as we dare as you only have around 14 psi to shove the mix in whereas the ex valve cracks open to a residual pressure of around 70 psi which gives a flow rate of around twice the inlet valve. Rarely (except for blown engines) does an ex valve greater than .68 times the inlet valve produce more power, in fact a large ex valve can reduce the bottom end power of an engine. If the ex valve turns out to be too small compared to the inlet valve, we can tinker with something called the valve time area, which is a function of the valve size and lift/duration of the cam. You can increase the ex valve time area by increasing the lift and/or duration of the exhaust cam, making the ex valve 'think' it is bigger than it is.

For blown engines we reckon a ratio of 90% ex to inlet...exactly the same as the old TF heads....and they work well with scs...and looking at the porting....arent those ex ports big and just crying out for an SC....must have been what the factory had in mind when they made em?



Peter
P Burgess

I have never heard you speak such sense as that Peter. That was exactly correct even sounded logical and right. As is always the case if logical thought is applied then 99 times out of 100 it works. Good post.

By the way I wasn't suggesting you other posts are poor far from it but that one sounded spot on! :)
Robert (Bob) Midget Turbo

Aha makes a change from me talking a load of boll**ks after three bottles of beer then?


What always gets me is some people tell me I should use large ex valves in naturally aspirated then others are stunned when I suggest large ex valves for forced induction! I cannot win either way.

Peter
P Burgess

This thread was discussed between 07/10/2010 and 09/10/2010

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