Club 80-90 Forums

Being Olde Skool and living on a hill I leave mine parked in reverse with the engine off and let it lollop onto the next compression and then put the handbrake on

Ian

ajsimmo wrote:No Martin...I think his handbrake's knackered so he parks in gear on a slope but it still rolls (slowly). Easiest answer is, er, fix handbrake.

Oh I see.....penny drops lol. So the OP wonders if there is something wrong based on the fact that his van moves when he uses the engine 'in gear' to stop the van rolling? well I never lol.

Of course it will move! pistons/compression rings, won't hold compression when moving slow...each ring has an end gap, albeit a small one but the compression will steadily leak by, however, this is no real measurement of engine condition.

Martin

The slope isn't dreadful but is enough to bump start the van. I know this as the battery is also knackered. Reverse will almost hold it. I'll still test the compression but you've made me feel much better.

Cheers

Ady

Put it this way...put a socket and bar on the end of your crankshaft and it can be fairly easily turned despite the compression, lean on the bar as each cylinder approaches TDC (top dead centre) and you can hear the hissing as the pressure escapes past the rings.
The compression 'works' because the pressure doesn't have time to escape with the engine running.

Each piston at idle is travelling up and down the cylinder bore nearly 30 times per second....take that to 5,000rpm and that speed increases to 166 strokes per second....I know, mind boggling but you can see how little time the pressurized mix has to 'blow by' the rings.Then compare this to each piston (there is obviously only one on its compression stroke at any one time) holding the weight of the van on a slope..the air slowly by-passing the rings over seconds or minutes.

Martin

{Of course it will move! pistons/compression rings, won't hold compression when moving slow...each ring has an end gap, albeit a small one but the compression will steadily leak by, however, this is no real measurement of engine condition.]

Yes being an old Rocker I soon learned the noble art of piston fitting. Our rule was circa 3-4 thou per inch of bore depending.

Sadly enough most people these days don't check the ring gap when they install pistons and every now and again I hear of sudden unexplained engine seizures after a rebuild.

CS