project 1980 Austin Princess

[Talbot]

20 hours ago, sloth said:

also combustion pressure can be affected by bore vs stroke, i.e smaller piston pushes less air but the same c/r 

That makes no sense.  It shouldn't matter what the geometry of the piston is, all it's doing is compressing air.  Whilst an over-square engine will have very different performance to an under-square one, if the CR is 9:1, then the CR is 9:1, so it compresses the same volume of air into the same clearance volume.

the one thing that would make a big difference to the compression test pressure would be the valve timing.  If the inlet valve isn't closing until a good bit after BDC, then it's possible that even a healthy engine would show a lower test pressure, as the piston is already rising in the cylinder before the valve is closed, so that bit of compression is "lost".

 

[vulgalour]

Water stopped falling out of the sky when I wasn't at work!

Good enough.  So let's do the wet compression test.  I've also included the figures for the dry compression test below for ease of comparison.

DRY TEST
Cylinder - First reading - Second reading
1 - 85 - 80
2 - 158 - 158
3 - 145 - 145
4 - 150 - 150

WET TEST
Cylinder - First reading - Second reading
1 - 148 - 148
2 - 160 - 155
3 - 150 - 150
4 - 155 - 155

Cylinder 2 seems like a bit of an anomoly but perhaps that's something to do with 1 having failed so there's a bit of leak through or something.  3 and 4 are probably okay?  The jump in compression on 1 was a surprise but perhaps that suggests that the rings are actually good and doing their job.

I'll open this one to the floor, I don't really know what these figures are saying beyond confirming the issue with the HGF is on 1 and 2.

[Talbot]

Other way around.  The fact that the wet test shows a jump up in compression pressures suggests the bore or rings are boogered.  If the figure had stayed the same, that would then point elsewhere, but the fact that the rings being saturated with oil has improved the pressure means there's something amiss with them.

How much oil did you use (as in, just wondering if it got into anywhere else to improve the pressures)

[vulgalour]

I used the very technical quantity of "a good squirt", I didn't have anything to actually measure it out that would also allow me to pour it into the spark plug holes.

[colino]

That reads to me that No 1 has a ring/bore problem, but I'd take the plugs out and using the anti-seize of your choice, squirt plenty down the bores and leave for a week.  Then empty the bores by spinning it on the starter, putting the plugs in and going for a thrash.  If your compression tests are the same after that, you ponder a DIY rebuild or sticking in someone elses second hand problem.

[vulgalour]

Going for a thrash not really an option when the head gasket has failed.

[captain_70s]

Is the sump droppable in situ or is it burried in gearbox and subframe and shit?

[vulgalour]

Gearbox in sump means removing the engine is the easier than dropping the sump.  Which is okay, I got the tools to do just that, it's just a faff.  No subframe to worry about, so that's something.  Current plan is to unbolt the sump and clutch assembly, remove the bonnet, and lift the block and head as one lump out through the top.  Once it's all on the engine stand, I can then get to more dismantling and inspection.  Car isn't consuming vast quantities of oil so I'm not really expecting horrors, hopefully we get away with a light hone and new rings and haven't got worn out bearings or the like.

I do find it less and less likely that the 75k is genuine on this car.  I blame Quentin Wilson.

[colino]

The cleaned up version.  It's already broken, you can't break it any more. 

[Talbot]

"A good squirt" could well have also wetted the head gasket area, and possibly even a valve or two.  That said, it's noticeable that even with oil in the bore, the compression pressure for cylinder 1 is still slightly lower than for the others.

I suspect that your OMGHGF is probably betwixt cylinder 1 and the water jacket.   It would be very interesting to to a leakdown test (as described earlier) to see if bubbles appear in the coolant.

If you are able to do a leakdown, the test is carried out with the cylinder at TDC at ignition.  You can move the piston down the bore a bit on either compression or ignition to see if it changes anything, but the first thing is a TDC test.

Or just* heave the engine out, whip the head off and see what's up.

[vulgalour]

I haven't got an air compressor so I can't do a leakdown test.  I don't have the space to put one either so it's not something I'm going to buy (even if I could afford it, which I can't right now) so I reckon the best bet is to pull the engine and start having a look inside it to see what's what.  A rebuild is pretty much unavoidable now but I've got most, if not all, of the bits I'm going to need to do it.

[captain_70s]

22 hours ago, vulgalour said:

I do find it less and less likely that the 75k is genuine on this car.  I blame Quentin Wilson.

Enough BL engines shat themselves in less than 10k that I'd not be surprised that some would need a light rebuild at 70k...

 

[vulgalour]

I'm still blaming Quentin Wilson on principle.

[Talbot]

On 11/16/2020 at 8:03 PM, vulgalour said:

I haven't got an air compressor so I can't do a leakdown test. 

Have you got a spare old scrap spark plug?  Given that I need to bring this wing up to you soon, I could bring a compresser with me and we could do a leakdown test there and then if you like.

[vulgalour]

I might in the spare head, I'm not sure.  I'll try and find out tomorrow, new garage roof goes on then so we'll be emptying some of the garage out for that.

[catsinthewelder]

 

Happy Princess day Angyl

https://www.daysoftheyear.com/days/princess-day/

[Rocket88]

22 hours ago, vulgalour said:

I'm still blaming Quentin Wilson on principle.

He's responsible for most of the ills in the world.................!😡

[Talbot]

On 10/26/2020 at 10:21 PM, Talbot said:

As for the compression pressures.  I'm only commenting that it sounds high, as when you're doing a compression test, you're turning the engine into a compressor.  It draws in atmospheric air at 1bar, and then compresses it to 9 times that pressure (a 9:1 engine), so you'd expect the maximum it could achieve to be 9 bar (132 psi).  The bit about volumetric efficiency is to do with how well the cylinder is filled before it compresses the air in it.  if it's 100% full, that means it's at 1 bar before it starts compressing.  Most engines run at less than 100% volumetric efficiency, hence the cylinder is still at a slight vacuum before the air is compressed, meaning the final figure is a little less than the theoretical maximum.

I absolutely don't doubt your book says 195psi.  I just don't understand how.

Ok, I am a complete idiot.

It took me until now, while pondering this while driving one day to realise the fundamental error I made in the waffle above:  Compression in a car engine is Adiabatic, not Isothermal.  I was putting numbers together based on Isothermal compression.  The compression happens so quickly there is no time for any heat (or at least very little) to be conducted away by cold engine components, meaning I should have been using Adiabatic calculations.

On that basis, 195psi is more than reasonable.  In fact, it indicates that the valve timing isn't closing the inlet valve until quite significantly past BDC (which is generally correct)

So yes.  Ignore my previous bollocks please.

[High Jetter]

Thank you for another schoolday, I'd forgotten about those measurements.

[vulgalour]

Proper Princess updates are going to be a long time coming so in the meantime, here's a video that tries to condense nine years of ownership into less than 20 minutes of content.

 

[vulgalour]

It's been a while.  Things are finally a bit more organised here so let's have a look at what's wrong with the Princess' engine and turn it around.

 

[vulgalour]

Another Princess update coming soon, and this one will have words and pictures.  Didn't bother with the last one since it's info you've seen before if you've been reading the thread.  Had the head off and back together again today, got too cold and dark to put the battery on and the distributor in so I'm saving that for tomorrow.  You'll have to wait for the video to see what happens, don't want to give you any spoilers here.

[vulgalour]

Progress has been a bit weird today.  I have an odd timing issue.  On the Princess, you've got a small toothed pulley at the top for the camshaft, a smaller toothed pulley at the bottom for the crankshaft, and a non-spring roller tensioner.  Both pulleys are connected by a belt (Gates 5024).

Now, when I fitted the brand new belt it was very cold indeed and while I thought I'd got the timing correct, today I found the timing was off a bit.  I reset the timing, removed and refitted the belt, and the timing kept going off.  The belt isn't slipping or jumping teeth (camera and Pat confirmed this) and after about a dozen removal and refittings of the belt, the problem has neither got better nor gone away.  With every revolution of the engine, the timing marks get further and further apart until what started as perfectly aligned becomes one tooth out.  I'm sure I could keep going and make it even worse but this is an interference engine so I shan't do that.  Camshaft and Crankshaft pulleys are nice and tight, and the tensioner is staying nice and tight too, the belt appears neither too slack nor too tight.

All I can think is this is caused by a stretched belt.  The one I've fitted is exactly the same as the one I've taken off (which I cut, since re-using timing belts is bad practice, so I can't refit it) so I wonder if maybe I've stretched the new belt because it was so cold when I fitted it, or that it was a bad belt to begin with.  Other than that, I can't think why the timing would be wandering off like this.

I'm going to order a new belt anyway now, I've had this new one on and off so many times that I can't imagine that its done it any favours.  I have had this issue before and was told "they can't do that" variously, I believe a new belt was the solution then too.

[cobblers]

Are you talking timing marks on the pulleys reference the engine, or are you marking the belt?

[vulgalour]

The marks on the pulleys themselves.  So, there's a mark to align on the crankshaft and one to align on the camshaft and those marks are shifting out of alignment somehow.  Everytime you rotate the engine to what should be the same point, the timing marks on the pulleys get 'further away' from each other, if that makes sense?

[cobblers]

Unless one of the pulleys has been changed, the belt has got to be slipping or not riding in it's groove properly. Even if it was stretching, you'd end up with inches of slack eventually,

Has it got the right profile teeth?

[Noel Tidybeard]

has the belt got the wrong number of teeth?

[cobblers]

Even if the belt had a different number of teeth, so long as it tensioned up it wouldn't matter really, there twice as many teeth on the cam pulley as there are on the crank pulley and that's that.

[vulgalour]

The belt is exactly the same as the one I removed, which didn't have this problem.  Same manufacturer, same number of teeth, same teeth profile.  The only difference between this belt and the one that was on is that this one has been slightly easier to fit, it's usually a right old war to get the timing belt on while this one hasn't put up the usual level of fight and been merely annoying rather than making me want to rage-throw spanners.

[Paul-l]

is one of the pulleys rotating slowly on the shaft? - perhaps the key has fallen out, or some engines use a taper fit on the cam shaft and rely on the nut being tight to keep things aligned