william sadler scribed:
Subject: tale of woe
> had a leak down test done. Here are the results:
>
> Cyl. # 1 2 3 4 5 6
> com 40# norm - - - -
> %loss 90 20 40 65 45 40
> There is obviously a crack in the cylinder head between 1 and 3.
Obviously? Not. What's wrong with #3? Compression is normal, right?
Sounds like the guy doesn't know how to either do or diagnose a
leakdown test. As I'd be real surprized to find a crack from
1 to 3 on a straight six engine (!), I'd suspect valves, or just
maybe the gasket. I'd like the see the actual compression #'s,
as well.
> If you take out the spark plugs in those cylinders
> you can hear air coming out of 3.
What you hear is more likley air getting past a badly seating or
cracked valve face on #1, into the manifold, which you can hear in 3
cuz it's valve is open when # 1 is (usually) closed. (check the firing order)
(Poor seating can be caused by carbon/oil deposits, or worn or
damaged valves/seats.) This failure could have resulted from
improperly tuned carbs, or could cause hard to balance carbs.
*IF* the head is actually cracked, the MGC head is quite robust and
should be easily repairable.
Since you've had the manifolds off recently, getting the head off
should be easy. Make sure you have valid compression test #'s
before you pull the head. If the above #'s are valid, and compression
for 2-6 is between say 125-150, I'd say it's time for a valve job.
Time to fit hardened seats & upgraded valves, IF you need to replace
anything. The quick and easy possibility is that you may just need
to clean off deposits & lap the valves. That'll cost a couple gaskets,
and a couple bucks for lapping compound. Worst (best?) is that it's
time for that full engine rebuild...
Does John Twist (University Motors, MI) do C work? I'd expect he
does, or know who does.
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