Boring, technical MGB update #348
I think I've mentioned that I've been fighting an oil leak since the engine was out. This leak has actually taken a few different forms. The most concerning of these is extreme vaporization at higher engine speeds(4500rpms+, with anything much about that essentially leaving a blue haze in its wake). In addition, it would dump a few ounce of oil every time the engine was shut down.
Aside from the environmental consequences, this also turns into a decent expense when the engine is dumping 1 quart every 50-100 miles. There are a lot of opinions and debates on oil in general and in specifics for the "B" engine, but I have settled on Valvoline VR-1 20W-50. This is the factory recommended weight, so there's not a lot of argument there. The B series engines, like a lot of old engines, are overhead valve(pushrod) engines with "flat" tappets. Unlike the roller tappets used on modern OHV engines, flat tappets have localized areas of very high pressure as the tappets rise on the lobes of the camshaft. In the past, zinc dialkyldithiophosphate(ZDDP) in the oil was used to form a sacrificial wear surface on the camshaft to reduce wear on the the lobes. Because the phosphorous can foul catalytic converters, the latest API oil specifications call for much lower ZDDP levels. This isn't an issue for overhead cams and for roller cams, where camshaft pressure is much less, and overall isn't an issue in the grand scheme of things since there are no current production street engines that use overhead valves with flat tappets. The "magic number" is roughly 1200ppm zinc, and many oils now have 1/2 to 1/3 of that. My car has flat tappets and no catalytic converter, so I want high zinc oils. I'm aware of three oils in the US market-all 20W-50-that retain this level. They are Valvoline VR-1, Brad Penn(Kendall), and Amsoil. The Valvoline gets the nod from me...it's not a "boutique" oil like the other two and is readily available at most any well stocked auto parts store, plus is about $6/quart compared to $8 for Brad Penn and $10+ for Amsoil. A half case(6 quarts) of VR-1 is $28 at Rural King, which makes it even more economical. VR-1 is marketed as a "racing oil" but is street legal and has has street-type additives(i.e. good buffering capacity and good detergents) unlike the black bottle, special order Valvoline racing oil that really is only meant to run one race and be drained. All that aside, even at its relatively low cost(albeit in the price range of most synthetics rather than conventional oils, even though VR-1 is conventional) losing that much oil that quickly is pricey.
All that aside, when the engine was out we changed every easily accessible gasket. On the oil end of things, it got a new pan gasket(it was nice to see the sump and bottom end condition), valve cover gasket, and replacement gaskets for the side covers/tappet inspection covers.
When I initially made the parts order, I ordered cork gaskets for the tappet covers. I emailed the list to my parts guy, who called me and said "Why are you ordering cork gaskets for those." He talked me into the fancy silicon rubber ones, and I was agreeable since they were about $1 each more expensive than cork. The rubber gaskets are quite bulky at 1/4" or so each, while the cork ones are about the thickness of a few sheets of paper.
So, the rubber gaskets went in place. They are easy to access with the engine out, but basically impossible with everything installed because they sit right behind the exhaust manifold.
I'd pretty much tracked my leak to these gaskets, as oil would puddle on that side of the engine and that side was wet with oil. The vaporization was worse with the crankcase completely open to the atmosphere(putting a small purpose made filter/oil separator on the crankcase vent rather than routing it directly to the carburetor throats as on the stock set-up-this creates enough of a vacuum to help pull out crank case gasses) but would still happen at higher RPMs. This 100K mile engine likely has a decent amount of blow-by, seemingly confirmed by what I was seeing in the oil leaks(and also somewhat low albeit consistent compression readings), but again it wasn't a problem before the engine came out.
I talked to John Twist(MG guru) about the problem and he too was concerned about blow-by, but also asked me if I was using "those G-D red rubber tappet galley gaskets." He went on to say that he will only use cork, as the rubber is just too thick and tends to distort and leak.
Even so, I managed to get a wrench on the front cover and tightened it about two turns. This just made it worse, as I'd inadvertently squeezed more of the rubber out. It's likely that increased crankcase pressure at high RPMs just was too much for the breather system to handle at it forced oil out the "path of least resistance." The vacuum breather hoses connect to a ported vacuum source(just in front of the throttle butterflies) and the vacuum in this area is relatively low when maintaining a constant speed. If I find it a continuous problem, I might end up moving the breather system over to the manifold since its vacuum is highest at constant RPMs/loads.
I needed some work done on the exhaust manifold due to snapped studs when we pulled it apart. The snapped studs are common due to their location and extreme heat stress. We'd jerry-rigged it together when we put it back together since we were trying to track down parts on a Sunday morning. Basically we ended up using bolts directly into the manifold for most of them-a sloppy but incorrect fix-but one hole was bad enough that it ended up with a nut and bolt-again a really sloppy fix. This left me with an annoying and possibly dangerous exhaust leak-the cabins aren't THAT tight, and I could hear "popping" from the exhaust manifold when driving. I didn't dare drive it top up, windows shut for this very reason.
So, finally I conceded and dropped it off with my local mechanic. He is another MG nut, and in fact has the MGA that I'm likely going to buy. I told him to do what he could on exhaust, but also to try and find the oil leak.
He took one look and saw the rubber gaskets and mentioned to me how much he hated them. Fortunately, he has a set of cork ones on the shelf. He hasn't finished the job just yet(he should finish it tomorrow) but they will be simple to change when he has the manifold off. He didn't charge me for them either, although I made a gentleman's agreement with him to order replacements when I put in my next Moss order.
So, the resolution to this is for anyone working on this type of engine not to use rubber tappet gaskets. Hopefully this will fix it.
The blow-by still needs to be addressed, but it's more than I want to tackle right now. Fortunately, piston rings can be changed with the engine in the car. The head has to come off-something that's not a huge deal on OHV engines-along with the oil pan. It's then possible to undo the connecting rod bearings and push the piston out through the top of the block. Of course, rod bearings get replaced also. As long as I can get the crankcase leakage under control, I can kick that can down the road a bit longer and pay put it off until it's time for a complete engine rebuild.
