As the title suggests. I don't know much about the engine. Seems to run well and drives well but has low compression on one cylinder (I'm told). Any
suggestions on possible causes or reasons for this? As it is a bus I'm contemplating buying I'd like a bit of an idea what I could be in for (best
or worst case scenario).
My thoughts would be that it has to be caused by one of the following:
Piston/rings
Cracked head
Valve or valve seat
The other 3 read 140 to 160 or so, the low one is 40 ish.
Any easy pre purchase ways to tell without dropping the motor and stripping?
squirt a little sewing machine oil into the trouble cylinder spark plug hole and retest, if the compression increases using this method it's most likely the rings.
So what would stand out as the most likely cause? It's number 4 if that makes any difference. And any problems using it like it is in the short term? Do you automatically have to replace stuff symmetrically? So for a damaged barrel or head do you have to replace the whole lot or is a one sided fix sufficient if there's one damaged valve? Or just do a top end rebuild and be done with it? Approximate costs - if you've done one up can you give me an idea? I know the type 4 motors are known for their repair costs. Can I just slot a good 1600 in there? Will that fit the 2 litre gearbox?
if funds available best to do full reco , as the compressionis all over the shop, and if you only do the top end the bottom end normally fails .
as a good kombi motor is so nice to drive and they pull up big hills in top gear. 
sometimes if the motor stuffed , which you will not know until its pulled apart. cheaper to do the Subaru change over.
very common fault is a failed valve seat on the type 4 heads, that would give the low compression. New heads are available, made by AMC, for about
$360 US$ each from AA Performance.
http://aapistons.com/shop/cylinder-heads-and-components.html?aa_engine_type=V...
I'm trying to decide on purchasing a 73 lowlight van (well DC actually) which would have originally been a 1600 I'd guess. Just have to factor in costs of what may be wrong to decide if its too much cost or trouble. Everything else is very good and daily driver standard which is what I want. Just the engine is the uncertainty. Not looking to do Subaru conversions. Too much involved I think.
I guess you could just drive it, but any car with compression down that low is just letting fuel go out the exhaust,
Subaru are so make easier to drive and heaps good on fuel .
this is a bit out there or the paint job is 
http://www.youtube.com/watch?v=MLhWTf8Q-fY&feature=c4-overview&list=U...
Could be something as simple as a closed tappet keep a valve slightly open...........and if you keep driving it it will kill the valve !
So is most of the rebuild cost down to parts or labour? If I do a lot of it myself like pull out, strip down etc does it help and to what extent?