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MG MGB Technical - Starting engine after rebuild-

HI all,

Finally at the stage where the engine is finished plumbed in and have test started.

After starting (it wasnt easy to start)It ran very ropey for about a minute and a smell not unlike gun powder came from the exhaust with a wisp of blue smoke. When pressing the gas pedal it didnt react.

I adjusted the carbs and tried again, same result. I did this a third time, same result.

I then turned the engine off. At least theres no leaks anywhere if anything positive is to be drawn from it.

Few of the engine specs:-

72 Block,Fast road head/ Piper fast road cam, HS6.

What could be the problem? Im worried that I will trash the engine before I get a chance to bed the cam in. Im thinking the timing is way off. I dialed in at 32 deg static using the front pulley. Engine turns round with sparks removed, very smoothly.
JS Ahlund

JS,

32 static? That sounds like it could be your problem. I'm too lazy to look up the static spec, but 32 is around what it should be at full advance. I think static is something like 8 or 10, but look it up. From all I have been advised, you are correct to worry about damaging the new cam if you don't get it running and up in the higher rev range for the first 20 minutes or so of running.

Charley
C R Huff

Thanks Charley.

I used your advice on setting up the carbs. I guess i should re set them again, as they are not the issue.

I just double checked the timing. I meant 32 at full vac advance, which id tried to dial in without a strobe using the front pulley. It is off at 13. Ill start at eight and see how it goes. Im going to try and find a static timing chart too.

Hopefully with a few - max 3 minutes total of running I havent damaged anything!

Breakfast and then back at it.

Thanks!

Jamie
JS Ahlund

A "wisp" or two is not unusual at first firing as assembly lubricant etc., burns off.
Full advance at 32deg is on the centrifugal (mechanical) advance somewhere around 3500rpm. Static will do at 10deg to get it up and running. What did you set the cam timing at? Also fast road cams often have different rocker clearances, usually bigger.
Allan Reeling

Thanks Allan for the reply.

I havent got out to the garage yet- Early breakfast/ late lunch with the family, I suspect they know im eager to get to my cave so it has taken longer than usuall. Funny bunch!!

Cam is at 104. Inlet/outlet are set to correct spec cold ill check them again after.

I was hoping the smell/wisp was burning assembly lube and normal.

I do have a friend coming by during the week with a strobe to help dial it in correctly after initial fire up and bedding in.
JS Ahlund

Are there any blockages in your exhaust system? This could also cause the problems that you are encountering. RAY
rjm RAY

Hi Ray,

The exhaust is new, I installed it saturday. Ill add a look over of the manifold to downpipe on the list of checks, thanks for the tip. I did have an after thought yesterday about cam timing but im very sure i dialed it in correctly, I checked like five times or more.

I checked the timing marks again. I have a pro race balancer and the 72 timing cover. The pro race ive used the zero mark on the scale. The timing cover- Ive discovered that I got the TDC mark back to front, thinking the first left mark was TDC when infact its the first on the right. So when ive thought it was 10 BTDC it is more than likely that its somewhere closer to 5 BTDC or perhaps even less.

Hope I havent damaged anything.
JS Ahlund

Jamie,

When you say the following, I don't know what you mean: "I just double checked the timing. I meant 32 at full vac advance, which id tried to dial in without a strobe using the front pulley."

Full advance timing would be done with the engine running at high RPM and has to be done with a strobe to be accurate.

Static is done with the engine not running, and with no advance of any kind in operation.

I would pull your #1 plug and check that TDC on your new balancer is correct.

Do you have ignition points in this car? If you have electronic, I don't know how to set static timing. If you have points, you can either use a test light or you can slip a cigarette paper between the points. With the engine at 8 or 10 or whatever BTDC, rotate the distributor while holding tension on the paper. When the paper comes out, lock the distributor.

Also make sure the distributor is firing #1 when #1 is on the compression stroke.

When you describe left and right marks for your balancer, are you using the correct convention of right & left as described while sitting in the driver's seat?

Charley
C R Huff

Full *vac* (which is what was stated) advance - or very nearly so - occurs at idle on cars with manifold vacuum. This could be anything from 6 to 24 degrees, *plus* any static advance (typically around 10), plus any centrifugal advance.

With an after-market balancer/crank pulley and a factory front cover i.e. timing mark it is essential you check that the TDC mark on the pulley lines up with the TDC mark on the cover when Nos.1 and 4 pistons are at the top of their stroke.

The TDC point on the cover is usually larger than the others. As timing is usually done when peering into the engine compartment, the crank pulley rotates clockwise when looking at the front of the engine, which puts the TDC pointer on the cover on the right, and the BTDC points left of that.

How did you set the timing without a strobe?
Paul Hunt

Just to reiterate Paul's point. You do need to check that indicated TDC is actually when No 1 piston is at TDC. It can be done with the head in place by working through the plug hole,enough to show a wild discrepancy, but it's more accurate with a DTI on the piston crown.
Allan Reeling

This thread was discussed between 05/07/2014 and 12/07/2014

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