Thanks, Bill! That's a keeper.
I guess my main problem is deciding between the "if it ain't broke"
theory and the "do it all while you're at it and save the hassle later"
theory. Pity I'm not wealthy, since I MUST get a top first, and that and the
engine will about do it for the year. I've decided after I do this motor,
I'll have to keep it to about $1k/year (ha!) in improvements (mostly
cosmetic, other than suspension), which means I may win a trophy in 2003 or
so. Not that I ever will win a trophy, I'm finding I drive it too much for
that!
I guess I'll decide for sure once I get the engine out and take a look
at things. As I said before, the temp and pressure are to spec. I don't know
the exact temp but last saturday (95 in the shade) I drove the car hard all
day, ending with a 2 hour 65-70 mph run home on the interstate. The temp
guage didn't read much over 'N', and the oil pressure didn't go below 25 at
idle after this "pounding".
Funny you mentioned it. I'm running pretty rich (too rich, judging by
the plugs and mileage) but I'm not sure about the timing. I HAVE noticed
more missing lately and significant "burble/wimpy backfire" on off-throttle
with about 1500 miles on the new points, so I'm going to check the points,
timing and mix this weekend.
Cheers!
Dan
73 B
-----Original Message-----
From: Bill Eastman <william.eastman@medtronic.com>
To: mgs@autox.team.net <mgs@autox.team.net>
Date: Tuesday, July 21, 1998 11:35 AM
Subject: Rebuilds, overheating, timing, other stuff
>Dan Ray has asked about rebuilding his engine. Most of the list has
>recommended doing the whole thing. I will offer my opinion on this as
>well.
>
>Almost everyone who spend time around the A asks what I do to keep it
>running so cool. We have had a fairly wicked heat wave here lately with
>temps in the 90's F and high humidity. During that time the A has run
>around 185-190 in normal driving and up to 200 after 40 at 65-70 mph on
>the freeway. It cools down right away once I slow down. I have done
>nothing special to the car. I did replace the water pump this year as PM
>but it didn't run any hotter or cooler with the Moss aluminum unit than it
did
>with the old cast iron pump that came out.
>
>I believe that the reason it runs cool is that the motor is "loose." When
I
>replaced the rod bearings they Plastigaged towards the top of the
>acceptable range. The bores had about .003" of wear and the standard
>rings went in with the gap just over the maximum listed in the book. I
>expect that the pistons are also a little looser than on a newly rebuilt
>motor.
>
>If you talk to racers, building an engine for power means setting the
>clearances as loose as possible and still have the reliability to finish
the
>race. Sprint engines are looser than endurance engines, for instance.
>This is because the tighter the clearance at the rod bearing, for instance,
>the more friction and heat are generated there. Also, higher volumes of
>oil through the bearings cool them more effectively. The down side is you
>have less time to run the engine before it is too loose and lunches
>something. In the A I also have lower oil pressure than typical although
it
>is high enough in my opinion.
>
>So, the reasons that the A runs cools are 1) the engine is nice and loose
>so the bearings and rings don't generate as much heat as they would in a
>tighter motor. 2) I keep the timing as far advanced as I can without
>causing detonation or kick back against the starter. 3) I run the A a
little
>rich. This make it idle funny when warm but otherwise it runs great and
>keeps cool. Don't overdo this however since you can start washing the
>cylinders and cause accelerated wear.
>
>So, in answer to the original question, I think that the best way to
figure
>out whether a rebuild is needed is to see what the clearances are. As
>long as they are within reason (Remember that the specs listed are for
>acceptable range for a new engine. You can probably run a little looser
>with no problems), then just replace the wear parts and go for it. For the
>rings, you can figure out how much wear you have by comparing ring
>gap just below the ridge and the bottom of the bore. Lacking a decent
>micrometer, the best indication of main and rod bearing fit is the
condition
>of the journals. If they look in pretty good shape then they will probably
>be OK. A little frosting in the center can usually be buffed out but if
any
>scratches will catch a fingernail then you should consider grinding the
>crank. For the cam bearings, if you can see copper you need to replace
>them. These are about the only thing you can't get to with the engine in
>the car so you may want to do it anyway since they are not that
>expensive.
>
>I expect that the A's motor will last another 30k miles before it needs
>attention to the bottom end. A full rebuild may have doubled that time but
>then again 30k is 5 to 10 years based on how much I drive the A so why
>worry. If all of the clearances had been brought down to minimum the
>engine would have a longer theoretical life but it would also be more
>prone to overheating. I believe that overheating has killed more MG
>motors than bearing wear so I think I made the correct decision.
>
>BTW- I believe that John Twist agrees with this approach (as far as the
>rebuild goes) so I'm not the only crazy person out there.
>
>I ran seven autocross runs this weekend plus 50 miles each way to and
>from the meet. The A was the only British car out the that never belched
>smoke or some vital fluid (other than a couple of 50 cent piece sized oil
>spots). I made the last two runs back to back then shut down
>immediately and the heat soak caused some fuel percolation but five
>minutes with the (bent) bonnet up solved that. This is with 82k on the car
>and new rings, rod and main bearings, cam, lifter and cam bearings, and
>umbrella style valve seals with new exhaust valves/ original intakes
>running in the original guides. I put in a new rocker shaft too. Nothing
>was boiled out although I did my best to clean everything. What more
>could you ask for?
>
>Regards,
>Bill Eastman
>61 MGA still the daily driver.
>
>PS- if I was to do it again I would have replaced the oil pump too.
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