In a message dated 98-11-26 11:27:57 EST, wmgilroy@lucent.com writes:
>> Now that I got the head off my 77 Midget (1500cc) I have more than a
few questions about what I am seeing. Just a recap, I took the head
off because I had very low compress cylinders 2 & 3 (something like
40 & 60 psi dry) and about 120 psi dry in 1 & 4. I also had high
crankcase pressure. Oil was coming out the dipstick hole. I was hoping
it was a blown head gasket between 2&3 and one of the oil galleys.
Those results indicate either a blown head gasket or bad rings / worn
cylinders
>> Looking at the head gasket it does not look like there is a problem
there. I don't see anything obvious (not that I am sure what I should
be looking for). The color of the gasket is the same i.e. no black
traces or worn looking areas.
Well it sounds like the head gasket is ok doesn't it? That leaves rings and
cylinders
>> Other things I am seeing. If you into the cylinder head where the
intake and exhaust manifold attach you see the following; dry soot
on the exhaust, and black oily deposits (sort of like oily carbon)
on all of the intake ports. These deposits are rather lumpy, you can
rub them off with your finger. What would this be? Worn valves guides,
rich carb, maybe?
The soot is fairly normal perhaps a rich carb (at this point the least of your
problems) The oily residue is indicative of bad valve guides and or seals. A
machine shop can disassemble the head and check the guides for wear. My gut
guess is bad guides.
>> The combustion chamber on the cylinder head looks ok. Not very much
in the way of deposits. The valves themselves are black, with some
of the exhaust valves being gray at the center. I guess they get
hotter?
Oh yeah way, way, hotter. This is normal
>> The tops of the pistons show the following. 1,2, & 3 have quite a bit
of hard black deposits on them. I cannot see any of the original piston
top. Number 4 has much less and I can see most of the piston top.
Sounds like the valve guides oil get into the combustion chambers and gets
burnt, that is the black deposits you see. This is fairly normal BTW.
>> I am trying to decide how I should proceed. I could just put a new
head gasket, put most of it back together and see if I get any
different compression figures. This would be the cheapest way. What
are the other logical routes to take? The closest I have come to
rebuilding engines is the 2 cycle dirt bike I had as a kid. That was
quite a bit different.
Well do you want to fix it or screw around? If you just put it back together
all of the existing problems will still be there unless there is a fault in
the head gasket that you have not observed or disclosed. From you decription
(which sounds accurate BTW) there is not a problem with the head gasket. IMHO
the problems with you engine are twofold first the valve guides are probably
bad, I would suggest new guides and a valve job (have the springs checked for
tension by the machine shop) quite possibly the valve seat will need renewing
the machine shop can advise.
Secondly and perhaps most importantly I think that you have a combo of worn
rings and worn cylinders. In line engines have a tendency to wear the
cylinders oval as the engine rotates. In other words over time the cylinders
get wider that they are long. (the engine on my B was that way when I bought
it) While this wear is not visible to the naked eye (it's measured in
thousandths of an inch It is more than enough to cause low compression and
crankcase pressure and oil burning.
>> If it looks like a rebuild, where should I look for some helpful
information? I mean what is required, what machine shop services
would I need, boring cylinders, fittings cams, checking cranks and
rods, etc.? What can I do myself, what should I check and re-check?
Since I do not know you experience level or the amount of tools that you have
here is a simple three step process to rebuild you engine
Step one FIND A GOOD MACHINE SHOP.
Step two have them measure and recomond repairs
Step three Rob bank to pay the guy from steps one and two
Only step three is a joke one and two are serious :-)
You can go the library and get you hands on a Motors Manual or a Chiltons
(the year isn't super important) go to the back and there should be a section
on generic engine rebuilding read it. You can also go to the book store and
browse through until you find a book that fits you knowledge base and gives
useful info. also feel free to e-mail me with specifics.
>> Two other beginners questions. 1) what is magnafluxing (sp?) 2) what is
shot peaning (sp?). I have seen both of these terms used when
discussing whether a part can be reused.
Magnafluxing is a method of crack detection that uses powder and a large
magnet (the powder is attracted into cracks and shows up visualy)
Shot peening is a way to relieve stress in a part like a connecting rod.
Basicly the part is blasted with shot (like what a shot gun shell is loaded
with) or some times glass beads (bead blasting) Talk to your machine shop
they will recomond these service if needed.
>>Looks like I might have bit off more than I wanted for this winter.
Oh well. Sorry for all of the questions, but this area is completely
new to me, and I am not even sure what I should be seeing. Thanks
for any advice.
At least it will keep you off the streets and out of the bars :-)
No problem I hope that this helps
Richard Ewald
Master Automotive Technician
67 MGB
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