MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Valve Lash

About 10 years ago I rebuilt my motor with a lot of the performance spec's from Barney's performance page.

I had to deck the block by 0.20" because a rill had burned through cylinders 3 & 4.

I decided to have 0.10" "eyebrows" cut into the block as suggested on the page.

I then added an APT VP11-BN performance cam shaft.

Unfortunately I didn't keep great notes on some of the resulting specifications. The most particular is the resulting Valve Lash I should set given my recipe above.

Is this something I can calculate or should it come from APT? or what?
Tysen McCarthy

For a special cam, use the valve lash specified by the cam grinder. If they don't tell you what the valve lash should be, don't run the cam. Do not assume it should be same as original issue cam.
barneymg

Thanks Barney. I'll reach out to APT.

It seems that they've changed the part reference.
Tysen McCarthy

You really took 200 thousandths off the block?
That's 22.5 cc.
And what is a rill?
Did you shorten the rods so the pistons didn't stick out?
Art Pearse


.018" inlet
.020" exhaust

It's a running clearance which is what most cam grinders quote, meaning set them at normal running temperature ( warm )

willy
William Revit

Art,

I'll have to go back to my notes. I'm thinking its a typo.

A rill is small channel that burned between the two cylinders.
Tysen McCarthy

200 thou! That's 5mm, I recently dropped the cr on my 1275 Sprite from almost 12:1 to 9.5:1 by fitting a 2mm gasket!
I wonder what the cr ratio is?
Graeme Williams

Typo by me. It was decked by 0.020". In addition to the eyebrows cut in I also had the cylinders bored out +0.030" to yield 1622cc

The compression ratio was calcuated by the shop is 8.8.
Tysen McCarthy

New question. The APT cam shaft calls for different gaps for intake and exhaust. So if the valves are numbered 1 thru 8 starting at the front. Which are exhaust?
Tysen McCarthy

No 1
-front-

1-Exhaust
2-Inlet
3-Inlet
4-Exhaust
5-Exhaust
6-Inlet
7-Inlet
8-Exhaust

-rear-
No 4

.018" inlet
.020" exhaust
for your camshaft
William Revit

2,3,6 and 7 are intakes
Art Pearse

0.020" off a block is OK. More ad you really need to look to your valve geometry (shortened pushrods will maintain correct geometry but you can only shorten after market pushrods). Failing to watch that can prematurely wear valve stems and guides as it imparts increased side force on the valve stems. Roller tip rockers also cure a minor misalignment, but costs a lot more than a set of shortened pushrods.
Bill Spohn

Just to close the loop on this. APT's spec for this cam is 0.016" intake and 0.018" exhaust.

The car is much happier after resetting the valves.
Tysen McCarthy

That's for VP11 then--16-18--interesting
William Revit

This thread was discussed between 06/06/2017 and 27/06/2017

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.