Man with spanners - thinks he's a mechanic

[ChrisL]

I managed to get into a rhythm with it. Nick's sorting me out some shims, nice bloke btw

[ChrisL]

And the scores on the doors
1 90
2 100
3 25
4 90

So it looks like #3 is still the problem

[DJ.]

Sorry to hear that.

[ChrisL]

Thanks DJ

Looking at the history of this there is a clearly a problem with #3,

Could it still be the head? I've had the valve seats re-cut and have all new valves and the shim gaps are all within spec. I got the same pressure on it whatever the test. Could it be an issue with the bore? If so why didn't a wet test change the result, unless I had a head and bore issue...

I'm thinking about next steps:
1. Wet test, if the pressure goes up then this has to be a bore issue. I'll definitely do this tonight;
2. re-build the other block I have, will need new bearings seals etc, but I didn't like the look of it which is why I'm using this block;
3. Leak down test, kits aren't too pricy but I don't have a compressor so will either have to rig something up with an old wheel or use a tyre inflator or bike pump;
4. send it out to get pressure tested;
5. send the block out to be re-bored and fit bigger piston rings, if that is an option or am I looking at new pistons?

Screenshot 2020-07-22 at 09.29.09.png (22.8 KiB) Viewed 2678 times

[ChrisL]

Just done a wet test on 3&4 and got 150 on 3 and 225 on 4

[ChrisL]

Taken the head back of the re measure the bores, as far as I can tell I’m getting 84.78mm everywhere. Also checked the other block I have and that doesn’t and is slightly ovalised so I’m reasonably happy my measurements are ok well okish! Where to go next? I’m thinking of dropping the sump and pulling no.3 piston to check the rings....

[DJ.]

It sounds a good place to start.

If the bore is round and smooth, the valves seal, new head gasket and the piston is sound it must be the rings. Unless I'm missing something

[Jasonmpk]

Hi, I've not rebuild an engine recently, but am sure there is meant to be a certain spacing around the piston for the rings to be seated in. i.e. with a certain amount of overlap to help seal each piston into the bore.
So another possible reason for your results could be stuck rings or just not spaced correctly around the piston, thus allowing for leakage past them.

Jason

[SteveRST]

Yeah, the 3 piston ring gaps are supposed to be spaced 120 degrees apart from each other i.e. so they are spaced as far away from each other as possible. But I'd imagine Chris would have known that.

Be interesting to see what the ring gap measurements on #3 are, but with compression that low I'd have thought it would have to be something more serious than rings gap being gapped a bit too big.

Good luck Chris! I admire your perseverance!

[Dick]

Piston rings have move around the piston ring groove when its running , yes on assembly space them out is normal practice. Yes sounds like you need to pop the pistons out of it chris and have a measure up.