Low comp on 1 cylinder. rings or valve?

[Tooheys]

I recently brought a SJ413 hard top that had a bit of a tired motor. I've done a compression test on the motor and from front to back:

No.1: 105psi
No.2: 210psi
No.3: 210psi
No.4: 210psi

When i did the compression test I did all cylinders twice and the motor was at operating temperature when I did the test. On cylinder 1 I thought it might be sticky rings so i sprayed a heap of degreaser down the spark plug hole and let it sit for an hour then cranked it over to push the excess out so i didnt get a hydralulic lock. I did a comp test afterwards and no change.

The motor doesn't idle well but will run when held around 1200rpm and will rev freely to redline. It also seems like it runs nicer the higher the revs are held. It doesn't blow any smoke out the exhaust although it does blow smoke out of the crank case breather. I also pulled the rocker cover off to see if I had cracked a valve spring but they all looked ok. Coolant in radiator seems good and there is no water in the oil and doesnt really seem to be burning oil in the short time I had the engine running.

Are there any other tests I can do without having to dismantle the engine. Do these symptoms sound like a burnt valve or something similar? Did putting the degreaser down there and then testing give me a true wet test for rings or should I do it again with some oil?

Thanks,

Paul

[AZZA'S HJ47]

would do a cylinder leak down test get cylinder 1 to top dead centre and go from there and yes a small amout of oil would be good to determine if it is a piston ring issue. it would also be a good idea for you to runs some top end clean cost about 10 bucks for a tin. it could be a head gasket also.

[Tooheys]

Is there a booty fab way to do a leakdown test as I only have a compression tester?

[AZZA'S HJ47]

not realy go to any mech shop any they would have one if not do a top end clean first

[brad-chevlux]

check the valve clearences next. Adjust them and recheck the compression.

do a proper wet test. put a little oil in number 1, wind the motor over a few times then recheck the comp. If you get a huge increase in compression it'll be rings, if it has no real change it'll be valves or a gasket

[dumbdunce]

squirt about 5 - 10ml of oil (ordinary engine oil) into the low compression cylinder and perform the compression test again. if the compression comes up significantly, the leakage is in the bottom end - piston/rings/bore. if the compression stays the same or only comes up a little bit, it's probably rings.

you can also disconnect the crankcase breather and look/listen while the engine is running - if the leakage is past the rings there will be a definite choof-choof-choof out the breather.

also take the radiator cap off while you do the compression test; if there is leakage past the gasket into the coolant, you'll see bubbles.

good luck!

[Chucky]

Once again dumbdunce has the answers.

[azzad]

Are you going to fix it or just want to know what is wrong with it?

If you intend on fixing it just pull the head and have a look; you are going to have to remove it to fix any of the previously mentioned fault anyway.

Dazza

[Tooheys]

Ok so firstly I pulled off the tappet cover and checked the vavle clearances and both inlet and exhaust are about .178mm which is
within spec.

Next I did the proper wet test with some engine oil and the compression shot back up to 180psi from 105psi. Also when i pulled
the breather hose off the tappet cover and put my thumb over it lightly I could feel the pulse of the cylinder firing and holding
my thumb over it for a couple of seconds it would build up some pressure.

So after all that I'm pretty sure the rings in the cylinder are fubar.

I'm going to pull the head tommorow hopefully and have a look what the bore is like. If the bore is not scored at all, will it
be ok to just hone it and replace the rings?

Are you going to fix it or just want to know what is wrong with it?

I want to try and fix it cheaper than what I can put a replacement motor in for. I've been quoted $795 for a 1.3L swift engine so
I'm hoping to fix it for atleast half that.

Thanks for all your help so far its helped me alot :

[dumbdunce]

.

If the bore is not scored at all, will it
be ok to just hone it and replace the rings?

if the rings are broken, chances are they will have taken out the bore too, which is in turn likely to have damaged the piston. if you need a super fast and cheap repair to get you through a year or so, then you might get away with just rings. you can also re-bore just that one cylinder and put a new piston and rings in it. it will not unbalance the engine.

[Tooheys]

Well just had a look on NZ's version of egay and there is a motor for sale in my area for $150 out of an 86 swift that "ran well when in car".

I'm thinking I would be better off with that because I dont think i could re-ring this motor for that price.

[dumbdunce]

Well just had a look on NZ's version of egay and there is a motor for sale in my area for $150 out of an 86 swift that "ran well when in car".

I'm thinking I would be better off with that because I dont think i could re-ring this motor for that price.

is it the same motor as what you've got now? get it, pull both apart, and build a good motor from the best of both. then you'll have a heap of spares and a motor you know is good. if the budget is the main issue, then yeah just get it, slam it in, and hope for the best.