Blacktop compression down on one cycliner

[alamo]

Ok so I have a 4AGE Blacktop in an FXGT. It's been running like shit so I got a compression test today. Three cycliners are at 200 and one is at 130. We then did a leak down test and found massive leakage out the exhaust system on this one cylinder.

What should I do next to fix this problem without spending too much money on it? It's just a daily driver thats gets thrashed now and again so I don't care too much about it but I just wont it running well and efficiently.

I've been given a ball park figure from a mechanic of $1000 to replace the head with another one thats been checked. He said I may as well replace the rings while it's opened up.

What are the other options or suggestions?

BTW what would have caused this problem on one cylinder? (The base timing was way out when I bought it?)

[xsspeed]

I would have said replace the rings and maybe headgasket. Wouldn't chuck the head before doing that and getting it tested again.

Bad rings on just the one cylinder is possible

[AceSniper]

if you think the ex side is leaking pull the head, and go from there, could be possible it has a slightly bent valve, or some other reason not sealing

[xsspeed]

if you think the ex side is leaking pull the head, and go from there, could be possible it has a slightly bent valve, or some other reason not sealing

Agree didn't think of that, there could be plenty of things but I wouldn't go chucking the head away!

[alamo]

Thanks for the replys. If the timing was way out and there was detonation would this have damaged the exhaust valves on cylinder 3? The other cylinders have good compression of 200 each. Why is just one of them down to 130?

[RedMist]

You can run the head so hot you burn exhaust valves. There are differences in temperature between cylinders dependant on the jacket shape and where the water enters and exits the head.

[rollaholic]

not sure why you would go to the trouble of replacing the rings - didnt think new rings would do much without a freshly honed bore to bed into. though if his $1000 included that, then you might as well?

if you can take the head off / on yourself, you could probably get the problem fixed for around $500 (presuming its just burnt a valve or two)

[Lloyd]

Take the head off, get the valves checked, replace the stuffed one or more

Rings is a bit of a bigger job, and not something you'd do just because the head was off

[d1 mule]

i agree with rollaholic and HRT rings wouldnt be on the to do list unledd you get the hed checked and its fine (athough seeing as its leaking out exhaust i doubt it)

failing that go down to ripco and buy a can of compression, there only like $12.99 that should sort it lol

[xsspeed]

F*** just reread the post and saw what he said about leakdown test, for sum reason I my wires cross when reading it.forget my 1st post.

A matter of interest if the leakdown test had revealed nothing what would most of you suggest? thats where I would have thought piston rings...

[rollaholic]

if leakdown test reveals nothing then there is not a problem

[xsspeed]

if leakdown test reveals nothing then there is not a problem

sorry for not being clear, if it reveals there is not a leak out the exhaust, but you are still down in compression

[AceSniper]

then you would be getting crank case pressure or out the intake port, or into the water system ??

[rollaholic]

when you do a leak down test, you put a special fitting into the sparkplug hole and pump compressed air into the cylinder with all valves closed (power or compression stroke). if compression is down on that cylinder, its because its leaking out somewhere.

basically like acesniper said, it could be intake valves, exhaust valves, headgasket (could leak into oil or water, but usually water) or piston rings.

you can hear / see the air escaping (from pressure gauge) and a bit of listening will hopefully tell you where from. exhaust valves = out the exhaust, inlet valves = back through the inlet mani... etc etc.

[MAGN1T]

It doesn't really matter..... it'll have to come to pieces.

Steve