engine help. a follow on from G13 timing thread

[3VILC]

I thought I'd start a new topic since its obviously not a timing issue.
Engine not running right and not tuneable. Replaced all leaking intake side gaskets. Compression 150 150 60 70. Lot of blow by from breather. No apparent mix of oil in coolant or vice versa.
Have now pulled the head. No signs of gasket failure. There is burnt oil in no3 intake port but not manifold runner, all others are clean. No3 combustion chamber also appears wet and oily. No signs of obvious cracks. Could it be leaky valve stem seals leading to or caused by burnt valves from the manifold vacuum leaks? Would the valves seals leak enough to be the noticeable blow by felt at the breather? I notice the oil tends to puddle above the no3 intake area perhaps that's why this one sucks it in worse. No 4 doesn't have an oily coating but there was a small dribble that resembled oil ran out when I removed the intake.
Thoughts/ideas? Will examine the valves closer in the daylight

[Crash bandicoot]

I'd be more concerned about the low compression on two cylinders.
if you reckon the head is okay and the gasket is ok and the valves are shut (leaking valve stems shouldn't effect it that bad)

that leaves one of two things....

ether the compression rings and oil rings have gone bye bye or you've got two bent conrods.

[3VILC]

Valves all appeared to close OK looking from the topside. But if the seats are burnt enough that might cause compression that low? Tried the oil down the plug hole trick before I started stripping it and that didn't improve anything so would guess rings are OK or really knackered. Will turn the cam over to open the valves and try get a decent look at the valves heads and seats tomorrow

[3VILC]

I too was concerned by the similar low readings on 2 adjacent cylinders, but the gasket shows no signs of burns in the gasket between the 2. Will check the valves and maybe run a straight edge over the head and deck in this area. Had an old bluebird that would religiously blow the gaskets and heads between these 2. Even brought a recon head that had obviously been welded in that exact point

[Mudde1]

When i cracked the head on mine it looked perfect and the gasket also looked perfect, but the head had a massive crack. Get the head tested by a cylinder head shop. i would be reasonably confident that would be your problem.
tony

[Campbell.s]

Have you done a leak down test?

[3VILC]

No leakdown test, its only a bush hack so I just want to get it going cheap as possible (which was meant to be the purpose of this engine, but nevermind).
I'd say you are right, there are no obvious reasons for the low compression, valves appear to be seating all the way around and are not burned or pitted, gasket wasn't blown, block deck and head face are not warped. But somehow 3 and 4 are joined together and oily so must be an internal crack between the 2 into an oil gallery, so I'd say head is rubbish. Bores look good, infact the only one with a light score in it is #2 which compression was fine in haha.
So i suppose my next question is, (to broaden my cheap search range) which other G series heads can be used with a G16 block (looks like 16v pistons), preferably with the 8V manifolds?? I know the 13A head fits since thats what it had on it, obviously the 16A, I pressume the 13B DOHC would have manifolds different again, what about the G15?
The reason I brought this engine was because I started with nothing in the engine bay, and this was cheap and complete from fan to prop shaft so wasnt too bigger deal if the block itself was no good tho obviously I was hoping to bolt it in and go. So don't really want to have to get another set of manifolds as well if I can help it.
I know FWD heads themselves are the same, but I would need a RWD cam since in the 2 junk G13s I've got here the dizzy drive gears are completely different (read JUNK been sitting in a paddock with the truck for X years so im not even going to attempt to salvage one of those heads haha)

[Campbell.s]

Out of curiosity how did you check to see that the valves where sealing properly?

[3VILC]

With my highly accurate eye-o-meter
Looks to be a consistent ring around the seating area, no burned/worn away areas or pitting, all sitting at the same depth. Its not that accurate I realize but nothing that would obviously account for such a huge lack of compression in 2 cylinders. I mean I could strip it down and try re-lapping them put it all back together, but I don't know if its worth the hassle, at the end of the day its just a trailer queen and I want to get it out and get it dirty lol. Easier to just find a cheap head and slap it on I think.

[Campbell.s]

Gotta love the trusty eye-o-meter.
Your right in that it would need to be some fairly obvious damage to the seat for the amount of compression you've lost, for your future reference the best way to check your valves are sealing when you've got the head off is to flip it upside down and fill the hollow of the compression chamer and valves with petrol, you'll see fuel run out the port of the valve that's not sealing works even if you don't have the valve springs on. Try it on the new head you get.

I'm a big fan of leak down testing when low compression is found, it takes all the guess work of what part has gone wrong wether it be valves, rings, head, gasket and it's very easy to do even if it is just a bush truck it costs you nothing but abit of time.

Just my 3 cents

[The WEHI]

Gotta love the trusty eye-o-meter.
Your right in that it would need to be some fairly obvious damage to the seat for the amount of compression you've lost, for your future reference the best way to check your valves are sealing when you've got the head off is to flip it upside down and fill the hollow of the compression chamer and valves with petrol, you'll see fuel run out the port of the valve that's not sealing works even if you don't have the valve springs on. Try it on the new head you get.

I'm a big fan of leak down testing when low compression is found, it takes all the guess work of what part has gone wrong wether it be valves, rings, head, gasket and it's very easy to do even if it is just a bush truck it costs you nothing but abit of time.

Just my 3 cents

Testing for good seat like above gently blow air in to the port and watch for bubbles in the fluid you use,

[3VILC]

Thats actually a good idea didnt think of how to do it now i've pulled the head off. I suppose I could have made/make a faily simple leakdown tester with a T piece and an airline coupling on my compression tester.. hindsight is a great thing haha.
Which leads me to another puzzle..if the crack, as it would appear to be, is inside the port area, it shouldnt effect compression really at all, would cause blowby if exhaust gas is being blown into the oil galleries. The plot thickens.
Might go try the petrol in the combustion chamber trick, and also pour some oil into the bore and see if/how fast that drains past the rings

[3VILC]

Campbell, you are a legend, that was exactly the sort of idea I was looking for. I was only thinking well I've pulled it to bits now so can't leakdown test it and don't want to pay to get the head pressure tested, didn't occur to me to pour some liquid in and see if/where it goes
Started with #3 since that seemed to be worst. Wound the piston up to just below the burnt ring at the top of the bore where its chamfered, filled with oil to the bottom of the ring, run piston down and up to same point, oil is still sitting at that level now, so rings are not shot. Wound cam around til both valves were closed, checked lash adjusters were loose so valves should be fully closed. Poured petrol into chamber, bingo dribbling straight out the exhaust port! Tried on #4, a little run from intake (i think, was a little careless with the pouring this time so couldve just been spillage) then from the exhaust port again. I would say since theres no obvious burning that its probably just soot buildup from the oil leaking past the valve seals.
So, prehaps it may be worth saving after all. Strip it down, give it a bloody good clean up, new valve seals, and try re-lapping them..this could also be the cause of the slightly low but less worrying comp on 1 and 2. Spec is 199-170PSI so 150 is not too bad for a bush hack really.
Or do I dare see how much a recon place charges for a head job I see a set of valve seals alone is $90

[Campbell.s]

Yea they're simple as to make this is how I made mine.

Old spark plug, cut off the earth and knock out the ceramic then just weld on an air fitting, hook it up to your air tank via a regulator and your away laughing.

Word of warning though, when you've got a cylinder on tdc compression stroke be very carful when you turn the air on as if it's not bang on the motor will spin with a vengeance so don't leave your spanner or ratchet on the crank.

been there done that got the scar to prove it

Glad I could help mate I hope it fixes your problem

[3VILC]

They look to be a pretty bloody simple head casting so I reckon I could clean it up pretty easy myself in a tub of petrol or something with some old toothbrushes etc. Valve seals arent too hard to do as long as the guides arent too far gone and need replacing. I think I can probably manage lapping them myself tho I've never actually done it before. Since the seats dont actually look worn or pitted just dirty I don't think they will need to be completely re-cut/machined.
I suppose theres no reason I cant try the cleanup and re-lap then perform the same petrol test again without even needing to buy valve seals and waste a new set of gaskets first. Nothing lost if it is still stuffed then except a bit of time and lapping paste

[Campbell.s]

I did the valves on my sj with a soft wire brush on a drill, then just lapped them in, worked a treat. Lapping valves is easy to do so long as you have the tools.

Where did you get the price for the valve stem seals? I got a complete engine gasket kit for not much more than that from repco, mind you that was trade price. Definitely recommend replacing the stem seals you don't want it to suck oil past them

[3VILC]

I'd say the seals are gone thats whats sucked the oil in, causing a lot of extra carbon and crud which is stopping the valves seating. So new seals is a definate. Its just a price I saw on trademe havent actually priced any up yet other than that, thought it seemed excessive just for stem seals tho.
I had thought of a similar idea to that, I've got an engraving type tool which has got tiny little brass wire wheels that might be good for cleaning the baked on stuff out of the valve holes. Might as well give it a real good scrub up while its in bits tho get as much crap off as I can. If all its going to cost me is a bit of time cleaning and relapping and a set of gaskets/seals to put it all back together then that sure beats having to buy another head that could be not much better. Any extra money was meant to be going on getting the brakes working properly not spending more on the engine haha..oh well, such are the joys of a project truck