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MGA Some questions for the MGA experts.

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burgundyben

Jedi Hopeful
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So we've had the car (MGA1500) about 10 days, this weekend we shot off to a vintage hill climb, about 100 miles from home.

I got the carbs about right, mixture is close although but I think out of balance, will come back to that after our hols. Want to pull a plug and see the colour.

Questions.

1. At about 3700 revs cruising we seem to be doing about 60 mph, this seems very slow for such high revs, a criticism of the MGA I have read somewhere, can I get a taller crown wheel and pinion?

2. On a consistent run at 3500 to 4000 revs the oil pressure drops to a shade under 40 psi (just had clean good quality 20/50 put in it), this sound ok?

3. I ran through the tappets as I thought she sounded a bit tappety, all at 16thou/0.4mm, but at motorway speeds she sounds very noisey from the top end, I have not run the engine with the rocker cover off, I'll do that and see how much oil there is coming up. why so much noise from the top end? Are they just like that?
 
Congrats on the new purchase.

Before I start, I will state that I'm NOT an expert. I don't like the term. I'll just say that I know some.

1. 3700 @ 60mph is about right. Someone might come up with the exact number, but given that neither the speedo nor tach are calibrated, they're only of mild interest to me. Your 1500 (and the 1600) came standard with a 4.3:1 CWP. The 1600 MkII came with a 4.1:1. Early MGBs have a 3.9:1 CWP that will fit. For a standard 1500, the 4.1 is as far as you'll want to go without completely kill acceleration.

2. Under 40psi hot is on the low side. Normally, owners are happy with 60 - 70 psi (25 - 30psi @ idle). It might be time to start thinking about an engine rebuild. Might also be a good time to consider upgrading the performance at the same time. Many, myself included, install an early MGB 1800 engine.

3. Yes, there will always be some noise from the tappets, even when correct clearances. If the contact surface of the rocker with the valve stem is worn (concave) it's very difficult/impossible to properly check the clearance with feeler gauges. Some people use a tool called (I think) a Klik-Adjust to overcome this.

Hope this helps.
 
So on a standard MGA 1500 what is a cruising speed that wont kill the car?

sounds like in the long term a MGB 1800 with a 5 speed box would get me a more relaxed cruising speed.
 
Hard to say, really. In my 'B I find that the engine just seems to settle into a comfortable "zone" around 3700rpm, as you seem to have found in your 'A. So a 4.1, at the same RPM will have you cruising around 5% faster. A 3.9, around 10%, i.e. 65 @ 3700rpm. An overdrive (or a typical 5th gear) is about 20%. An 1800 'B engine will pull this, but it's a bit much for a standard 1500. Some will say they cruise at more than 3700, but given the oil pressures you're seeing, I'd just use the car to enjoy the B roads while you get organized with a rebuilt engine. You've got2 advantages over me. Distances in the UK are much smaller than here and the roads much more suited to enjoying an MGA. And Sierra 'boxes were never sold over here, so 5 speed conversions are much more expensive.

As you're new to the 'A world, perhaps you haven't found this site. It's the most comprehensive MGA site that I know of.

https://www.mgaguru.com
 
Yes, thanks, the mgaguru site I had found, I think I read most of it before I bought the car, not much work got done for a couple of days....

So in summary, I need a rebuilt 5 bearing 1800 with a type 9 box.
 
That would make a lovely combination. My 'A, bought last year, sounds like the engines like yours, at least as far as the oil pressure goes. But it's a tired 1800 GB engine with 4.3 rear ratio. I haven't had the time to work on it much, other than the bare essentials to keep it available for touring the back roads. But I do have 2 4.1 CWPs and2 3.9 CWPs in stock that I'll be trying. With the torque available from the 1800, I don't think I'll miss the 5th gear. But a 5 speed with a rebuilt, enhanced 1500 might work as well, as 1 - 4 would be somewhat near the same with 5th available for quiet A-road & motorway cruising. Maybe someone with that combination can comment.
 
Ref - MGA Derek post - "3. Yes, there will always be some noise from the tappets, even when correct clearances. If the contact surface of the rocker with the valve stem is worn (concave) it's very difficult/impossible to properly check the clearance with feeler gauges. Some people use a tool called (I think) a Klik-Adjust to overcome this."

Photo below shows a valve clearance fixture I made to directly read valve clearance on a dial indicator instead of using a feeler gauge. If anyone is interested in making one I would be glad to send instructions or post on this site.
It should take care of the problem MGADerek mentions.
p5270020.jpg
 
burgundyben said:
So in summary, I need a rebuilt 5 bearing 1800 with a type 9 box.
Click to expand...
No, the standard unit is fine. If you want more power than you can get from the MGA engine then that's another matter. But a rebuilt MGA engine is quite durable and has a character different than what you would get from a 5-main MGB engine. I can refer you to someone who did just such a conversion and was disappointed with the "modern" feel of the engine.

That said, I do have a 3-main 1800 in my MGA and I feel the power is perfect for the car. I don't know what year model MGA you have, but if it's a 1622 then don't expect much of a power increase from the 1800. A 1500 is the only one of the MGA engines I would say will be significantly lower in power than the 1800. I wouldn't bother replacing the 1600 or 1622.

A 5-speed makes the car more pleasant on the highway but keep in mind it will again feel modern and will take away the vintage feel of the car somewhat. If this doesn't bother you then no worries. With additional effort you can also fit an early MGB overdrive, which is essentially the same as the MGA gearbox, only with an overdrive attached giving six forward gears.
 
If you do install the 5 speed you have to modify the tunnel as I believe it is wider than the stock 4 speed.
Also, MG rocker arm shafts do wear out making proper valve adjustment difficult which could add to valve train noise.
 
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