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MG TD TF 1500 - MG TF1500 cam timing

Hi, am going through a minor rebuild on my TF 1500, and I'm just reinstalling the camshaft. Have lined up the marks on the chain wheels as specified in the wsm. However the manual states that the inlet valve should start opening at 5 degrees before TDC.I have measured carefully and it seems to start opening at aound 20 degrees before TDC.
I am not sure how this can happen or indeed if it is a problem.
Any ideas?
Thanks
Paul
P Hicks

Paul
You've probably got it right-
Are you using the normal running .012" valve clearance for checking the timing-?
There is a different spec of- .037" for checking camshaft timing--some books mention it, some make you hunt for it--
Hope that helps
willy
William Revit

Thanks, Willy. I have got the head off at present so am using a dial gauge directly on the cam follower. Even allowing for the 12 thou clearance there is still a problem. However 37 thou might make the difference. I'll have another look tomorrow.
Paul
P Hicks

15 degrees is close to being 1 tooth out on the crank wheel or 2 on the cam wheel. Are you sure you gat it right, I always photo the chain wheels just to stop the "did I ?" when the cover is on for my own peace of mind.
Ray TF 2884

Ray Lee

Hi Ray, yes I have counted and recounted the thirteen and fifteen links many times. The engine is out on an engine stand so it is an easy check.thanks
Paul
P Hicks

Paul
Something in my memory bank says to ask did you have the engine right way up when you set the timing?

Graeme
G Evans

Paul
The .037" is a valve clearance spec for checking timing
If you're direct on the cam you'll need to divide that by the rocker ratio -1.38 :1
So that would be 0.27" at the cam for the 5deg btdc checking timing
I reckon you'll be very close

willy

The actual running timing spec is different as you can understand with .012" clearance and is quoted as flywheel timing
William Revit

Nothing to do with the timing issue but what a good suggestion Ray has. Digital photos cost nothing and as he says you can then eliminate previous work when a fault occurs.


Jan T
J Targosz

Willy i previously stated rocker arm ratio as 1.38: 1 it is ( nomilly ) 1.50:1. Also I have read checking clearance as .021" .....! More mud in the water!
Len Fanelli
( More to follow)
Len Fanelli

Well, in desperation I temporarily put the head and rocker gear back on. I used the setting Willy mentioned, .037 clearance on the valve heads, and amazingly it all worked out within a couple of degrees max, so thanks for all your help everyone.
Best wishes
Paul
P Hicks

Good stuff Paul--full steam ahead

Len, I always thought they were 1.5 but when I went to double check what I had said about timing the book quoted 1.38 so that's what I went with-----------don't know
The .037" checking clearance must be somewhere near right if Paul's timing has checked out ok
Depends on who wrote what in which book I guess
Cheers
willy
William Revit

It is off topic - but who knows?

The rockers of an 1948 BMW based engine (BRISTOL) should be adjusted. There is an advice in the WSM. I never had seen before that a warm engine has more clearance than a cold engine. Any hints?

W_Mueller

If they give a spec. cold .002" as noted there, then that is what they want you to do.
Then they are saying as the engine warms up and the metal grows with heat the clearance will usually change and they are saying that in the case of your engine the clearance will increase to the quoted .008"

An engine cools off quickly and to set them hot requires quick work which is impossible with some engines
It's easier to set clearances cold if you have the spec.

Even with some aftermarket camshafts that only give a hot running clearance, I usually just set one cylinder to spec. hot and then leave it to cool right off without touching anything---Then when it's nice and cold measure that cylinder to get a cold clearance spec and go through and set the lot at the new cold spec

willy
William Revit

Thank you Willy

when you do so - did it ever happened that after cooling off the clearance was minor than hot?
W_Mueller

It depends a lot on the particular engine and if it's pushrod or overhead camshaft
an example
A racer MGB with a running clearance of .020" hot, when it cools down the inlet will be about .018" but the exhaust will be up around .022"
But an air cooled alloy engine like a 4 stroke lawnmower, you can set them cold at nearly nothing and as they warm up and the alloy grows the clearance will grow heaps out to 6-8 thou ---bit like your Bristol
Some other cars like say an E type Jaguar or Lotus Elan where the camshaft operates direct on top of the valve(almost) the inlet clearance stays almost the same all the time whereas the exhaust decreases a little with more heat into the valve--Usually these are checked cold because of the amount of work/time involved in doing the job so cold the exh will have a greater setting clearance compared to the inlet to make it all good when it's hot and running
Hope that answers your question
If not more than happy to go on if you want
willy
William Revit

This thread was discussed between 25/06/2019 and 28/06/2019

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