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MG MGB Technical - garage find - update

Big day today. Got the engine running for the first time. No idea when it was last run. Could be a year ago....could have been 15! I did a compression test before I fired it up. 180, 175, 145, 100 from front to back. The engine turned over slower as the tests proceeded. I had my foot down hard on the accelerator as well. If the rear butterfly wasn't opening as far as the front would this explain the difference in readings? Just trying to get the simple things out of the way first. I'll try again later when the battery has charged a bit. I found the white wire and white and black wire for the coil but couldn't find a white and black to connect to the distributor. I did find a separate wire which I'd labelled up as having come from the distributor so connected that in place of the white/black. Fired up without too much cranking.

One odd thing I noticed is that the tachy now goes full scale if I turn anything on e.g. it will go full scale if I switch on the wipers. Very odd. Hopefully the car will be road ready next week after I get the brakes done.
Steve Church

Steve. Well done. As to the compression readings, they are of some value on a known good engine or one which you have kept track of for some time. Much less valuable on a new engine which is known to have been laid up for some time. Get the engine running is the first step. Then, check the torque on the cylinder head studs followed by setting the valve clearances. Any of those items might account for a lower than expected initial compression reading. Then, with the cylinder head properly torqued and the valves properly set, run the engine for a couple of hours (need not be all at one time). Pull the spark plugs and put some upper cylinder lube into the cylinders and let it sit for a day or two. Turn the engine over, without spark plugs, to help remove any excess upper cylinder lube/penetrating oil from the cylinders. Reinstall the spark plugs, start the engine, run it up to operating temperature. Then, shut the engine off, drain the old oil and replace with clean oil and a new filter. Then, you are at the stage when you might be able to run a compression check that will give you some idea of the condition of the engine. Too many possible variables right now to make an intelligent determination.

Les
Les Bengtson

Thanks for the info Les. On the topic of re-torqueing do I slacken the nuts first then retorque or just tighten straight away?
Steve Church

Steve-
Do not completely loosen the nuts during retorquing. Instead, just back them off enough to get them moving, otherwise you will be measuring the torque to break the stiction between the nut and the stud rather than the torque that results in the necessary stretching of the stud. Note that a cast iron cylinder head should be retorqued while the engine is hot, while an aluminum alloy cylinder head should be retorqued when the engine is cold. Be aware that the manufacturer of both the Fel-Pro and the Payen resin cylinder head gaskets recommends that they not be retorqued after initial installation.
Stephen Strange

Thanks for the info. I don't know what manufacture gasket was fitted only that there appears to be some copper content from looking at the joint.

Les, what is the reason for putting upper cylinder lube into the cylinders. Is it to free up any stuck piston rings? What would you recommend as a lube. Redex? 2 stroke oil?
Steve Church

The engine will crank slower the longer it goes on, if it doesn't start, you are discharging the battery! If it now starts and runs you can ignore that. As long as it is charging anyway.

Those compression pressures are almost certainly *not* to do with the rear carb butterfly not opening fully, but it is an easy thing to check. Redex may well help the rings free and seat, seems to me you have little to lose either way now it is running.

Possibly something to do with a bad earth connection causing the tach to go full scale, don't know what year the car is (and it's expecting a lot for us (or me at any rate) to remember) but many years did share an earth connection between instruments and wipers and heater at a bolt high up on the scuttle behind the dash on the right hand side.
PaulH Solihull

Steve. Yes, upper cylinder lube, or a penetrating oil, will help to free up stuck piston rings. So, in some cases, will simply running the engine for a while. The objective is to free up the piston rings, ensure the valves are fully closing, and put a few running hours on the engine. At that point, a compression will be a more useful diagnostic tool.

As to the resin type head gaskets, I know Peter Burgess has told me that he does not retorque them after initial run in because his conversation with the Payen representative who told him it was not necessary. But, I have seen no official statement, at least by Fel-Pro, that retorquing will cause any damage to the head gasket. I have done it on several rebuilds, using the Fel-Pro gasket set with resin head gasket, with no problems noted. The highest time engine only has 40K miles on it, but that includes several cross country trips. If the head gasket could be damaged by being retorqued, I would expect to see it by now. What I have seen, with both the the original style and the resin head gaskets, is a loss of torque on the cylinder head studs--sufficient so that using a torque wrench set to 50 lbft, I did not have to back off several of the nuts when retorquing. (A trick shown to me many years ago was to set the torque wrench at the required reading, then go over the cylinder head bolts, in the required pattern, to check for any studs which have lost torque. Interesting what you find when you do this before the annual tune up.)

Please let us know how you get on. Again, anytime someone gets an engine that has been sitting for an indefinite period up and running, they have done well.

Les
Les Bengtson

This thread was discussed between 30/09/2010 and 01/10/2010

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