MGB Roadmaster

[rficalora]

The timing changes at the dyno were done at the distributor.  At least that's where I saw folks make the adjustments.  I didn't see anyone adjust the timing box.

[MGBV8]

Rob,

Great job on the starter bracket!

The only backfire I witnessed was at Jim's back in Feb. We discovered it blew a block off plug off the carb causing a very rough idle due to a vacuum leak.  The timing box was on the car.

My understanding from the bit I read on this timing box was that is that we actually had the unit disabled. If the trim pots are fully clockwise, they are disabled (factory setting).  Maybe we should just remove it.  I do think that  the start retard would be a very good idea, though.

MSD Programmable Timing Computer PN 8981

http://www.jegs.com/InstallationInstructions/100/121/121-8981.pdf

[rficalora]

It's backfired on most of us.  Only seems to happaen when it's warm.

There are two revisions of the 8981.  Most of them have a start retard.  The very early ones don't (at least that's what I've been told).  I've also been told it's more likely someone cut the regard wire and that could be - there's a plastic protector designed to hold the wires where they exit the box & it was falling off so the wires have been pulled on at some point.  I'm going to have a closer look later this week.

If I'm reading the manual right, there is no way to wire it in & have it disabled.  With all three knobs turned down to their min settings, we'd be getting 10* of retard from wherever mechanical is set, then it'd start adding 1/2* for every 1000 RPM (+ whatever the distributor and vacation add).

[MGBV8]

This is what I saw:

Timing Curve Adjustment Controls
There are three adjustable potentiometers on the side of the Programmable Timing Computer.
They are adjusted by loosening the lock nut and then turning the pot with a flat blade
screwdriver. All of the knobs are set at the full clockwise position at the factory, which means
that they are Off and there is no timing curve.

[rficalora]

Had a thought...  car seems to be starting easier even when hot.  Hasn't backfired at all.  Thinking that without an engine ground maybe the starter wasn't seeing the full voltage so wasn't spinning as fast &/or with as much torque - contributing to the backfires.

[BlownMGB-V8]

Makes no sense Rob. There was a heavy cable from the battery to the transmission tailshaft, about as good of a ground as you can get. The aluminum and cast iron of the transmission case and the block may not be as good of conductors as copper but they more than make up for that in sheer mass, or in the cross section of the conductor. You would have to have a copper cable nearly an inch in diameter to equal it.

Honestly I don't think that has anything to do with it. There have been periods before when the car never backfired.

Have you been able to try anything with the PCV flame trap/oil separator?

Jim

[rficalora]

Haven't messed with the flame trap/oil separator.  Bought a baffled gromet.  It fit the hole, but not the PCV.  Will check out some traps this weekend.  A good test will be when PJ drives it north.

On the ground, logic would agree but if that's the case, why was the braided stainless oil pressure line getting so hot?

[roverman]

Clan, oil line should be at oil temp,(pretty hot). Has anyone verified that distributor is "always" returning to static timing for starting phase ? If distributor is is sticking  intermittently, this could cause the random back-fires. Good Luck, roverman.

[flitner]

July 3rd we got a report of a package car fire, the investigation led to the hydraulic line to the hydroboost from the gearbox creatng chassis ground due to service previously performed had left the ground srap off. I have also seen similar things happen on airboats. A simple voltage drop test while cranking it over can help find the culprit.

[BlownMGB-V8]

I think the ground cable might be double ought and was a new 6v cable from autozone. At any rate it is serious overkill for any 12v car. And I believe it was bolted through the transmission tailshaft counterweight attachment boss with about a 2-1/2" long 3/8" diameter stainless bolt and probably has stainless washers, lockwashers, and maybe even a nylock stainless nut. Nobody has had any reason to mess with that since it left here and I verified the connection personally so I'm pretty sure the ground is adequate. But additional grounds for safety and redundancy are rarely a bad idea. Just let's not go overboard with it and neglect other things that are needed worse.

Only time will tell if the engine will sneeze again but I'm betting it will. Possibly Art is on to something. Maybe we should lock the advance mechanism and use the box to set mechanical advance. Otoh, Jeff Schlemmer built the distributor so I would hope that it is right. Odd things can happen though.

Jim

[rficalora]

The roadmaster.didn't have an engine ground but I added one.  I ran it from the starter to the spot where the battery ground was terminated on the granny so should be a good ground.  And, I've noticed the tach isn't bouncing around.  At least not around town.  Haveent had it on the highway since getting it going again.

[kstevusa]

    can't have too many gounds, but only the ones that count are the soild connections. With the tach bouncing, appears something was not grounded adequately.  SAFETY FASTER!

[BlownMGB-V8]

That is sort of redundant Rob, but it won't hurt anything.  Aluminum is the next best conductor to copper and of course the entire transmission and bellhousing is aluminum, so saying the engine didn't have a ground is not really correct since it is rather solidly bolted to the bellhousing, which is solidly bolted to the tranny case,  then the extension housing, the ground cable, and then the battery. So in fact there is a very solid and substantial ground all the way to the starter using the most massive and effective conductors in the entire car. What you did is sort of equivalent to running a small signal wire alongside a massive buss bar. Doesn't hurt anything but completely unnecessary. So I would be very surprised if any change could be traced to that addition. The starter bracket otoh, now that was a very nice piece of work, and to my mind at least, absolutely essential.

Jim

[madmax]

I'm with Jim.   That ground cable was MASSIVE-- it's hard to believe there would have been any engine ground issues.  

That being said, Rob is there and experiencing and seeing what he has.   1st hand knowledge beats us out in the bleachers.  :-)

If problems persist, the ground/voltage drop test is probably a good idea.  (Eh, stranger things have happened, right?   For instance, is there a gasket between bellhousing and tranny body that-- despite hardware-- is blocking the flow of ground?   Hard to imagine, but...)  There is a reason they put ground cables RIGHT to the starter bolts!


RE:  distributor.   Pardon my ignorance, and this is probably a question that only Jim can answer, but IF the dang thing started and ran (-ish) here, why was this control box necessary?  If it isn't giving the start retard, uhm... what IS it doing?     Given the number of people that have and are going to drive this car, I would vote for a K.I.S.S approach.  (That's "keep it simple, stupid!")   The less black boxes, timing adjustments, knobs to fiddle...etc., the better!  (READ:  people will try *anything* to get a car started!  How would you ever know if the setting was returned correctly?)

I would assume pretty much ANYONE getting behind the wheel of this thing  would know what to do with pts and condenser!  And it's an easy spare to carry.

Already we've heard two or three different versions/interpretations of the INSTRUCTIONS for this control box!    That's not good....  No way for one person to help diagnose with the other, etc.  

My vote:  if it's note providing a specific, necessary utility to the car, then I'd remove it.  

(I now realize why it's there-- it's probably the rev limiter, isn't it?  :-)  )

Cheers,

M

[BlownMGB-V8]

Yep, rev limiter. But with a 6000 rpm chip. :-(  Could be 4800 considering the dyno curve.

Jim

[MGBV8]

For instance, is there a gasket between bellhousing and tranny body that-- despite hardware-- is blocking the flow of ground? [/qoute]

Max......I'm laughing my ass off! A bellhousing to tranny gasket?  Is there really such a thing for a manual trans?

[roverman]

When the laughting subsides, good point Max.Perhaps you meant between the tailhousing and main case, as we ALL know, has one ? As I recall, JB stated, the ground was hooked to the Tail Housing ? This build is quite similar to a standard 455 bbb. Why then should it need a starter brace, when so many thousands don't ? Other than a rev. limiter, why not a re-curved HEI , that we KNOW is not sticking on partial advance ?  Good Luck, roverman.

[BlownMGB-V8]

Even with a gasket or O-ring there are at least 4 bolts holding the tailshaft on. I could MAYBE see one of them becoming insulated,  but certainly not all of them.

And what about the millions of cars that just use a ground strap to the body? Is that a good ground? Iron and steel are rather poor conductors compared to aluminum or copper. Didn't MG originally ground the battery to the battery box? How much current density do you think can be handled by a circular patch of sheet metal just slightly larger than the attaching bolt, which was probably 5/16" iirc? Way less than a large aluminum casting I'll guarantee, and then going every which way through spot welds, rust, and a steel body tub to finally arrive at another ground strap,  even if it does go directly to a starter bolt,  is a considerably higher resistance path than a heavy copper cable directly to the tailshaft. But don't take my word for it,  ask Dan Masters.

As for that brace, the OEM fat body starter had a nice big footprint on it's cast iron nosecone to spread the impact loads. The gear reduction starters have a smaller footprint in cast aluminum. Doesn't take a lot of thought to see how that might be a little more prone to failure under impact loading. The end brace gives a tenfold increase in the ability to resist those impact loads, and you can calculate that directly from the half-length of the footprint divided into the distance from the mounting bolts to the starter bracket.

So now is it possible for an open or a high resistance path to develop? Sure. All we need to confirm that is to look at all the homes burned down by aluminum wiring installed during that misdirected heyday back around the 50's or 60's. So a resistance check is probably a good idea. But I don't think the car has been in service long enough or under harsh enough conditions to cause galvanic corrosion on such a massive scale as would be required to raise the resistance to a measurable degree. Still, not a bad idea to confirm it and it doesn't take much to do a measurement. If it was causing a problem. Which I don't believe it is. Especially with Rob's jumper wire.

Jim

[Todd McCreary]

You already have a ground run to the tail shaft.

Is there any particular reason you didn't just ground to one of the starter bolts?  It only amounts to another ~2' of heavy gauge cable.  Depending on routing, you might even have enough slack to stretch it right now.

"Best" grounding practice would be to ground the neg terminal of the battery to the frame or roll cage with a secondary 2 gauge cable run direct from the neg terminal to the starter.  Although that comes into play more in high compression engines that are also prone to high temp operating conditions.

[BlownMGB-V8]

Yes I suppose it would. I guess that is why we did it the way we did. Perhaps we should install a frame and roll cage.

Jim

[BlownMGB-V8]

I should apologize I guess, I got alittle miffed with all this concern about what should never have been an issue in the first place, while we ignored the crankcase venting issue almost entirely. To me that is a much more important concern. The wiring works. And even if it didn't Rob's fix would cure it. But the crankcase venting is almost certainly the source of the high oil consumption, and a remedy needs to be tried before winter.

There have been suggestions to partially tear down the engine and if we did that it would have to be during the cold months. But I hope nobody is expecting me to be involved in that unless we have first proven that the engine isn't sucking the oil down the carburator, because until we do we are just as likely to still have the problem afterwards and it would be a lot of wasted effort for nothing. If someone else wants to do that,  fine. Just don't expect me to do it.

I have extensively researched engine ventilation, written articles on the topic, cured real world oil consumption problems by using proper ventilation tecniques, AND traced BBB oil consumption problems directly to inadequate separation of oil from vapors coming from the lifter valley through the pcv plumbing. Well guess what, we have inadequate plumbing. So I found two flame arresters/oil separators on ebay for under twenty bucks that should have plugged right into the grommet and the hose and which should have cured the problem once and for all. But here we are getting ready for another long trip with plans afoot to buy a quart of oil every 150 miles. My math may not be that good but I think the separator is the cheaper option.

Jim

[Bill Young]

I agree Jim, we do need to address the oil consumption issue and the oil seperator would be an inexpensive solution to try. We have 9 days to get it installed before PJ picks up the car, is that doable? Rob? I'll buy the part we need if someone will just point me in the right direction.

[rficalora]

I'm happy to install it.  Haven't had time to get one but if you find one, have it shipped to me & I'll install it.

[BlownMGB-V8]

http://www.ebay.com/itm/ONE-FORD-OIL-CRANKCASE-SEPARATOR-ASSEMBLY-PART-E6ZZ-6A785-A-NOS-FREE-SHIPPING-/251109627240?pt=Vintage_Car_Truck_Parts_Accessories&hash=item3a774cd568&vxp=mtr
This unit is made for a much smaller engine so flow capacity may be less than desired. However I think it should fit.

 http://www.ebay.com/itm/MAGNUM-PCV-ENHANCER-OIL-SEPARATOR-Positive-Crankcase-Ventilation-Filter-HHO-/160704646989?pt=Motors_Car_Truck_Parts_Accessories&hash=item256abe4f4d&vxp=mtr
This unit is a universal fit durability of the housing may be questioned.

 http://www.ebay.com/itm/120805477947?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
Flame trap for Rover V8. Probably a good choice.

 There are others and suppliers like Summit, Jegs, etc will carry them as well. Search: flame trap, oil trap, oil separator and flame arrester.

The critical features are a single inlet and a single outlet, in sizes compatible with the manifold grommet and the pcv plumbing to the carb. The pcv valve will need to be retained. It should be oriented vertically if possible.

Jim

[Todd McCreary]

I should apologize I guess


Eh, sometimes I'm a little short for certain rides and a little bit slow for certain races.