I’ve had excessive pressure in my engine ( type 4 standard carbs) for a while. It’s been getting progressively worse and after a 1000 mile trip to Cornwall, Devon and Bath, I’ve bit the bullet and done a compression test. Her are the results… Comments would be appreciated. Sent from my iPhone using Tapatalk
Rings a bit worn but nothing serious, No.2 has a bigger problem that may also be rings as it went up so much when you presumably squirted some oil in to get the higher readings. 150 is pretty high. 1,3 & 4 look ok/good. Good move doing the test before ripping the engine out, knowledge is power.
Could a valve issue cause the lower reading on cylinder 2 ? …. although the increase in value after squirting in some oil might suggest not .
Only one way to find out. Any valve gaps closed up on your trip? Next thing take off the rocker assemblies and see if the stems are all sticking out the same, but hardly worth the effort as you know that heads coming off. You could check the head nut torque before you take the head off, it would be worthwhile to know if you have any loose ones and if so which ones.
Was only asking, because when I reset valves after my petrol in oil incident, the right hand valve spring on cylinder 2 seemed to look as if it had some sort of deposit on it …. not smooth like all the others. Will remove the rocker assembly and have a closer look.
Main thing is to do all the tests you can't do when it's apart beforehand. Hence the compression test and head torques. You might find you have a valve problem but you'll need to take the head off to fix it and when you do take the head off you'll be able to see a lot more i.e. evidence of leaks between head/cylinder, cracked heads, loose seats, oval exhaust valves, valve that have been leaking, piston/cylinder damage, broken rings. Being able to link the before and after head removal evidence can only help. But you know all this.
Wasn’t sure if head(s) could be removed with engine still in bus…. will look more carefully when I’m checking the head bolt torques and valves.
Sort of, if you pivot the engine down, but unless you're stuck working in a loose stone car park like me it's a lot easier to take it out. Remember to take the exhaust and HXs off first while you can get at the head HX nuts.
Well, I obviously misremembers which valve was potentially the issue. The far left valve on cylinder 2 can be wiggled and the valve spring can be pressed in and turned. Hopefully the photo will show the difference between the good and bad cylinder/ valves. Looks like the head may need refurbishing/ replacing…. It has a VW marking on it …. is that a good or a bad thing? Sent from my iPhone using Tapatalk
That soot comes from exhaust going up a badly worn valve guide. There is only one way to find out what is going on now and that is disassembly. Although the USA would have you do a leak down test or at least try to get some compressed air into the cylinder with the valves closed at TDC and listen for where it sounds like its hissing out from. Turning it over by hand might even produce enough distinct wheezing.. You probably get a little puff of smoke when you start the engine - another symptom of the worn exhaust valve guide. If the leakage into the head was extreme, then that could be a part of engine case pressure. But another part of that could be problems with the breather system being blocked.
This is the state of the air filter and top of engine (hopefully) showing the breather. Sent from my iPhone using Tapatalk
Interestingly, my no.2 cylinder also lost a lot of compression about a year ago, coming back from Techenders. I bought an endoscope from Deptech and poked it in the plug holes and the inlet manifolds, and found all my valve guides were in a perilous state. No. 2 had come right out and a piece of brass had buzzed around. Although I got the whole engine rebuilt, I suspect the no. 1 cause was the valve guides. it seems there are two types of guides. One has a step in it, and the other is just an interference fit. I had the latter. I’d be interested to know the merits of the two types.
I would guess loose guide now moved enough to be stuck holding the valve partially open. We'll when you get the head off.
I’ll be dropping the engine and taking the heads off to investigate further. I’ll leave the fitting of new guides to a machine shop ( assuming that it’s feasible.)
I’m presuming that it the last photo above, you’d normally have the short stub of pipe on the idle plumbing system connected up to the valve under the plastic intake to the rh.carb.
No point dragging the engine out if there's nowhere to put it other than out in the rain to be pinched, it's safest for me to leave it trapped in the engine bay.
