MG Sports Cars

Help required if possible.

I own a factory '73 MGB GT V8. I would like to know if there is a way to "accurately" measure the camshaft/valve lift without having to dismantle the top half of the motor to see if the camshaft is worn or not.

The motor is still in the car and it has standard hydraulic lifters.

Any ideas?

Pull one set of lifters, if they're badly worn you can bet the cam is as well..

And while I'm here, never put new lifters on an old cam.

Ivor

Thanks Ivor,

Your suggestion regarding pulling one set of lifters is what I am trying to avoid, however I realise that it might be the only way to do it. I was hoping that there maybe some "trick" way of measuring the lift with a dial gauge at the valve end without having to do this.

Ian

Yes measure the lift at the valve via the retainer using dial gauge. Rocker arm ratio is 1.6 so devide by that to get cam lift. Chech all 16 valve. Do you know the lift of the cam that is in the car?

Mike,

I believe it is a standard V8 cam therefore according to the manual it should have .39" or 10mm lift.

Not having worked on a car with hydraulic lifters before, it appears to me that an accurate reading can't be obtained due to the unknown clearance that would be attributed to the tappet clearance in a motor that does not have these lifters. I have read that to "dial in a camshaft" a solid lifter has to be used instead of a hydraulic type so I suppose that speaks for itself as I am endeavouring to basically achieve the same sort of thing.

I was just hoping that maybe some "very smart person" had lost a lot of sleep over this issue and come up with some brilllant way of achieving this exercise which is so simple with a motor that has normal tappets. It would appear that to obtain the desired figures I will have to remove the inlet manifold, rocker gear, etc. Damn!!

Thanks for the input.

Ian

Ian,

I think all the hydraulic lifters will collapse a similar amount. This will give you an indication to a bad lobe compared to one another. Chances are if you have any miles on the motor they could be bad. Of the 4 Rover motors I have pulled apart all had at least one bad lobe. Usually near the back of the motor. Yes your best bet is to pull the intake, not really a big job once the coolant is drained.



Edited 1 time(s). Last edit at 04/07/2014 11:04AM by mstemp.

You should be able to measure lift directly from the lifter by taking the pushrod out even with a hydraulic lifter. A dial indicator probe won't put enough pressure on the lifter to add any preload.

First, rotate the engine until the lifter is sitting on the cam base circle. Afix a dial indicator to the cylinder head and insert the indicator probe to touch the lifter. Rotate the engine and read the lift directly.

If you can also attach a degree wheel, you can measure duration, lobe centers, and lobe separation angle as well.

Quote:

Rocker arm ratio is 1.6 so devide by that to get cam lift

Don't count on it. Actual ratio will be something less than advertised.

Carl is right, multiply by 1.55.

Don't trust the ratio at all.
It varies all over the map.
You can change it just by moving the rocker towers around.
Jack's method works
But the best way is to pull the lifters and look at the cam up close and personal.
Pulling the intake is pretty easy.
And if your worried about the cam wear then the valley gasket is probably about done as well.
So good time to change that out while its apart.

Cheers
Fred

Fred,

I think I would also agree with Jack. This will require the removing of the rocker assembly, which I have no problems with and will check this over the coming weekend. I will let you know what happens.

By the way with the motor in the car I cannot fit a degree wheel.

One other question that somebody maybe able to answer is, if some or all the cam lobes are warn, will this affect a cylinder compression test?

Kind regards all

Ian

Ian,
The definitive answer is,
it depends.
Worn cam lobes and lifters can change valve timing dramatically.
For instance. A worn exhaust lobe and lifter can delay exhaust opening enough to raise the cranking compression by a surprising amount.
A badly worn engine can show compression #s that look very good but still run like %$#T.
If you've gone far enough to pull the rockers. Then its only a few more minutes to lift the intake and do a proper check.
While the rockers are off you can do a leakdown test as well. Which is a far better indication of your engines condition.
Cranking compression is a useful tool in some instances. But really, if your engine is running well, the cranking compression is most likely going to be fine. It won't tell you that a problem is coming, It's a tattletale, it lets you know that the failure is already here.
But you already knew that because the engine doesn't run quite right.
Cheers
Fred

Fred,

Thanks for the succinct answer. To put you and others in the picture, my car hasn't wanted to rev over 3500rpm. All the normal electrical components have been replaced, coil, points, etc., that one might expect to cure the problem but this wasn't to be.

I started looking for other mysterious gremlins deep inside the motor e.g. worn camshaft. My wife reckoned I was paranoid as I kept detailing to her that if the camshaft needed replacing I might as well pull the motor out and do a complete overhaul which she was none too pleased about as she knew that she would be pressed into service as the "mechanic's labourer".

It got to the stage that I convinced myself that there was a major problem with the motor so I took your advice and made up a "leak down tester". Instructions via the internet. I used the wall mounted regulator of my compressor, some spare high pressure hose, an air gauge from a disused tyre gauge and some brass air line connectors. I then removed the porcelain out of a spark plug and glued in a piece of copper tube so that it connected to the air hose. When all put together the wall regulator was set at 100psi and when connected, the cylinders showed leakages of between 92 psi (8% loss) and 96 psi (4% loss).

I think these readings are within reason so I shifted my line of thinking to fuel. This morning I recalled way back in the mid 70's when I owned a Toyota Celica and it suffered from a similar problem which turned out to be a blocked fuel filter. I really did not think that it would cure the problem, however, I disconnected both hoses on either ends of the filter and placed a piece of copper tube bypassing the filter. Gave the car a run and "hey presto" - fixed the problem! All I need to do is get another filter and hopefully many more miles of happy motoring without coughs and splutters of an engine that didn't like to see 3500rpm on the rev counter.

Thanks to everybody who had input into solving my problem.

Regards,

Ian

Glad to hear that it turned out to be such a simple problem.
It highlights my mantra to all my technicians.
If you have a problem, start at the beginning, check everything step by step, don't skip a step, and for god's sake don't guess.
The answer will come.
If you make a reasoned, rational assumption, that turns out to be incorrect. I'm behind you 100%.
However, if you take a WAG and you're wrong, I'll ride your ass through eternity.
My guy's think I'm magic, but I'm not. I've been around long enough to experience a ton of mistakes.
I don't trust anyone, I do my own checks, and if something doesn't make sense then it's probably wrong.
It brings to mind my son in law's 32 roadster.
He and his Dad built it together when he was a teen.
It runs a 5.0 TPI IROC engine that, with few exceptions, never really ran right.
They brought it in to our shop in the late 90's and we went through it. Did the basics and fixed a few other problems. And had it running strong.
Over the years it's performance deteriorated.
They had taken it to various performance shops and had cam swaps done, ecu changes and even a new wiring harness.
It drove so badly that his dad lost interest and my son in law bought it from him.
My son in law showed up at the house one night wanting to do an engine for the rod.
We formulated a game plan for the car and I mentioned that the 5.0 could easily meet his needs.
He said that it wouldn't even spin a tire so he wasn't interested.
I said that's nuts. We better have a look.
The short story is, the K+N carbureted fuel filter that was installed along the way wasn't up to fuel injection flow rates.
We put in a proper filter, returned all the "fixes" back to normal, and the 32 now does 12's all day long.
It still runs the 5.0 today and everyone is happy.
So the lesson is. Start at the beginning, check all the basics, make sure that the problem makes sense, and follow through in a logical order until you find the problem. Most things turn out to be simple. Even me.

Cheers
Fred

Ian,

Did you put a small orifice or restrictor in the middle of your leakdown tester? FAA regs require a .040" orifice. also, make sure the the piston is at TDC & the valves are closed.

Fred,
It all comes down to experience. Thanks once again.

Carl,

Yes, I blocked off one of the brass air line fittings with two pack glue and drilled a 40thou hole. Didn't have to worry about TDC as I removed the rocker assembly. It all worked fine.

Regards - Ian