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MG MGB Technical - I don't even know anymore

Hello all

I've run this one by you guys in the past, and recieved some very knowledgable advice, but so far no luck. I have a new development, though it is not yet known if the problems are related, and thought I might re-pose it to some of you more knowledgable about cars than I. So, here's the rundown...

Fall 2000:
engine overheats, burns head gasket
between cylinders 1&2. A valve is bent,
several seats not sealing properly
head is rebuilt (magnafluxed, converted
to unleaded, new valves, guides, springs,
stem seals, skimmed, chambers volume
matched)

Winter 2000:
head replaced. Great difficulty in tuning
with apparent missing on #2 cylinder.
Fuel economy reduced, #2 cylinder seems to
fire again, but difficult to determine.
Fuel mixture strength problems dastardly.
Rear is ok, but front is always lean. Car
reaches reasonably driveable state.
(Using HIF approx age 3 yrs)

Spring 2001:
fuel lines augered out, fuel pump tested
for output, fuel filters changed weekly
for approx 7 weeks (rust) after which
changed at 3 month intervals, float bowls
cleaned often. Carbs disassembled,
inspected, reassembled. jets blown out
grose jets replaced with needle valves.
fuel filler cap replaced. New spark
plugs, plug leads, distributor cap, rotor
(Lucas 45D Approx 1yr old)

Summer 2001:
replaced timing chain (loud rattling
noise) -- bad tensioner; new chain too
(Duplex chain)
Alternator failure(approx 1yr old)
--rebuilt
Clutch failure ( QH clutch, approx 30K mi)
--release bearing exploded
--replaced with Borg&Beck all round
replaced needle valves with grose jets
Fall 2001:
more carb tinkering, timing adjustments,
no luck...very frustrated...considering
Toyota alternative

...if you're still with me up to here, thanks for your patience...

1 Day Ago:
started up with loud clattering sound at
idle, disappearing at rpm in excess of
2000, load is ineffectual on noise. At
idle, #2 cylinder found to be not
combusting (sparks to block, compression
approx 135 psi) #1 cylinder seems fine,
as noticable drop in rpm as plug lead
removed; however,knocking also disappears
Related? I don't know. Sure hope so.

The car is a 69, HIF SU's, K&N's (recently oiled) 45D dizzy, fast road cam of unknown
spec, .030 dished pistons, unleaded head, standard sized valves, balanced con rods, crank, flywheel, standard capacity oil pump. There is a slight leak at one end of the oil cooler and a slight coolant leak around #2&3 on the head/block interface.

I guess that's about it. I must say, the past year has taught me much in the way of anger management and budgeting, but I'm to the point that I'd just like the darn thing to run right. If anyone has any ideas, insights, points I may have missed, empathetic stories, whatever, please let me know. Thanks a lot for any help, and also for sitting through such a long tirade.

Mike
Mike Lord

Mike,

I'm guessing, but here are a couple of things to check: You say the timing chain is worn, what about the rest of the engine - cam and lifters? Bent push rod from the bent valve? Worn rockers and shaft?

Sorry to say it, but you might as well tear it down and overhaul.

Good Luck,

Bud
Bud Goetzinger

Mike, Sorry to hear of the struggles and I certainly can appreciate your frustration.A couple of things to add to the items suggested by Bud , above ....
* The cam of "unknown origin" to use your description, may not be accurately ground or may have been damaged (is bent) by PO or someone else prior to fitting.
Getting a reputable machine shop to check the dimensions and lobe spacing may be a thought.
* Check the pushrods especially Nr 2 as Bud suggests.
* Has the block been dimensioned (ie checked for accuracy?) There may be distortion around Nr 2 cyl in the block rather than the head.
* The fuel system and carbs seem to be an on going problem but SU's in my experience usually are reliable once set up properly. Any carb shops near you? Perhaps a thorough inspection by someone else may reveal a clue
Apart from that not having access to the car my help is limited to what is suggested here. Please keep posting whatever you find. Cheers, Pete, Sydney, Australia.
Peter Thomas

Based on what you've reported--sounds like when the engine overheated in fall 2000, the bent valve was caused by contact with a piston which may have cracked the piston or damaged the ring land (wouldn't be no. 2 would it?).

When knocking goes away when the plug wire is removed often means a bad rod bearing.

Only a tear down will tell for sure.

Wayne
Wayne Pearson

Mike,

I have to second Peter's statement about the cam. Problems with one cylinder can stem from the fact that they share an intake port. So one cylinder robs the other. This usually happens when you go to a long duration camshaft.

The fact that it's only happening on the #2 cylinder sounds to me that the intake lobe on your #1 cylinder may be ground improperly or bent.

When the engine was put together was the cam timing set with a degree wheel or by the match-the-dots method?

You should be able to check the timing without removing the engine by using a dial gauge on top of the pushrod. But I'm not sure about having the clearance for the degree wheel.

Lin
Lin

Mike,

i would have to agree with the others, pull the cam & have it checked. As for the the loud clanging from the 1st cylinder it's difficult to 100% determine what this is without pulling the engine & stripping. Your probably not going to want to hear this but pulling the engine & re-building may be your best bet, this way you eliminate everything & start a fresh. If you do decide to rebuild don't be daunted by it the "B" series engine is simple & this BBS helps a lot.

Good luck & let us know if you come up with anything

Scott
Scott Ralph

There is only one way forward - pull the engine and recondition it.

You say # 2 has 135 psi = what about the others?

What is the hot oli pressure?
Chris Betson

Mike,

I'll chime in with the rest and recommend a complete rebuild. If you want to do it yourself, I'll lend a hand. If you want it done quickly (but done right) give me a call or you can come to the Club meeting tonight, info at http://www.SanDiegoMGClub.org. I'll Email my number direct to you offline.
Paul Konkle

Thanks for the input so far. I have been poking around a little this morning (college student, kooky schedule) and figured I might get a better look at things with the valve cover off. Pretty soon I had removed the rocker assembly to find a noticably shinier spot on the shaft of the #1 exhaust pushrod(about 3/4 the way to the top, around where it protrudes from the top of the head. It is possibly 1/8" in height and is visible about 90% the way round (like a tight c rather than an o). None of the rocker arms or pushrods looked warped (vis. inspection only), and all looked kosher except for the above mentioned wear. Just some more info...

Mike
Mike Lord

Thanks for the offer Paul. The engine has about 30k on it, so I am hoping not to have to do it again for a while, but maybe... As for the meeting, I 'd like to attend, but plans for the night might preclude that.

Mike
Mike Lord

Mike, a not so scientific but useful method to quickly check pushrods for bending is to roll them on a flat surface - a table or bench top will do. It should become pretty obvious which ones are bent and to what degree. Just an old trick learned too long ago. Good luck!
Hotwire

Mike,

just a suggestion but it would really useful to at least let Paul & maybe some others from the MG club have a look & a listen to the engine. This BBS is great but there's no substitute for actually seeing & hearing the offending beast.

Scott
Scott Ralph

This thread was discussed on 08/01/2002

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