piston ring de-tensioning

jgra1 · Post by **jgra1** » 21 Oct 2008, 22:02

could only do a warm test.. did it on my cyl #4

http://4.bp.blogspot.com/_2fj8MH_LeQ0/S ... ession.jpg

tester seems ok .. cyl 4 seems ok, dads engine..hmmm

Head off Jim as you say...

handyman · Post by **handyman** » 22 Oct 2008, 08:29

Hello John, if you are sure your gauge is working correctly, you should be able to do a blowdown test on your father's engine. A blowdown test will tell you whether it is HG, rings/bores or valves that are causing the problem. What is the mileage on the engine? Has it been de-coked, especially if it has been using suspect diesel?

If you do not know how to do it, PM me for procedure.

Handyman

jgra1 · Post by **jgra1** » 22 Oct 2008, 10:02

hi Hm...

90 psi across the board....
I am now thinking one of two woodruffs has gone.....

If the timing hole in the flywheel is always showing TDC, and either the cam or cranksprocket has moved, how can I prove that? Would No 1 and 4 inlet lobes be vertical in an ideal world? or, maybe there would be clearance between the 4 relavant buckets at TDC?

Just thinking of a test I can get him to do today.... to prove a bad woodie...

Interested in the leakdown/blowdown test anyway although not sure I [he]have all I need to do it...

Post by **CitroJim** » 22 Oct 2008, 17:45

jgra1 wrote: Just thinking of a test I can get him to do today.... to prove a bad woodie...

If a key had let go, I reckon the valves would have collided with the pistons. I'm almost certain there is nowhere the cam can come to rest that would leave all valves in such a position as to not contact. I tried to find if such a position existed last time I replaced a cam and couldn't. At least two valves are always wide open.

However, a quick check is to bring the engine to time and look at the cam lobes for the two outside cylinders (1 and 4) one, and I can't recall which, will be on the firing stroke and both valves firmly closed (cam lobes upward) and the other will be more or less on the "overlap" with both valves just open a bit.

Look too for a tad of "lost motion" in the cam when rotating the engine a little backwards and forwards on the crank pully.

jgra1 wrote: Interested in the leakdown/blowdown test anyway although not sure I [he]have all I need to do it...

If you have an airline, easy. Just rig up an adaptor to screw into a glowplug hole with a line to the compressor. Tee off a 100psi pressure gauge and have a good tap between the air source and engine.

Cylinder on TDC firing stroke (valves closed). Admit air into the cylinder until the gauge reads (say) 100psi. Turn off the tap (to hold the air in) and watch the gauge. Time how long the pressure takes to fall 15% or so. If it disappears in a short time, sealing is poor, if it stays up for ages, the cylinder is good.

Do a wet and dry test to determine rings or valves.

A bit rough and ready perhaps but it can be made very cheaply. A good cylinder should hold for some time. Test and prove on a known good 'un to get a feel before trying it on a suspect engine.

Pleiades · Post by **Pleiades** » 23 Oct 2008, 10:57

Just to throw a new spanner into the pile.

About 3 weeks ago I had a massive overheat in my diesel L200 (yes I know its not French, but it does serve a purpose so stop throwing stones at me)

The nitty gritty was that the new rad that I had fitted about 2 months before failed and with all the dirt on the dash, I never noticed the gauge going up, by the time that I saw the steam it was too late, the engine was realy hot.

After a cool down I tried to start but had low compressions on all 4.

The result was a cracked head.

Lucky me had kept an old engine from a mates L200 that had a broken crankshaft, so a quick head swap, a warranty rad, a head gasket and cam belt, all is fine.

I do feel that you will have to take the head off and get it pressure tested, unless like me you are lucky and just happen to have a spare good one around.

Regards
Martin.

jgra1 · Post by **jgra1** » 23 Oct 2008, 14:35

Martin thanks....

there is a spare engine in Hailsham which is not to far from me.. could take it up, and throw it in and bring other back for repair... at least it could in theory be done in a weekend, whereas a head-rebuild is a few days minimum with skimming etc (assuming the head is rebuildable)

Newcastle is just too far really for two trips

John