Author Topic: Minimum Cylinder Compression numbers needed ??? (Read 7625 times)

Peter · « **on:** September 01, 2007, 09:52:10 am »

Just checked the compression with my new tester from harborfreight on my 87TD and 3 of the cyls came up to 340psi and the 4th cyl was at 310psi...seems to be low to me, but not sure...I am useing 5/40 synthetic and I have not driven the car since last winter which at that time the car started immediately in -15C/5F with one cycle of the glow plugs...

Patrick · « **Reply #1 on:** September 01, 2007, 10:39:42 am »

Does seem low....... Had one here that was iffy last winter on a bad day with about 420 lbs across all 4. If it starts good in the winter don't worry about it! Maybe the guage is a little off. Got another guage you can screw on the tester?

burn_your_money · « **Reply #2 on:** September 01, 2007, 11:13:55 am »

Synthetic makes all the difference in the world in the winter time. I'm pretty sure my car has low compression (around 350) but I can't check it because of a crack in my head. I can start it in -40 without it being plugged in. It's not happy but it will start. My battery's kind of crappy too

jtanguay · « **Reply #3 on:** September 01, 2007, 11:32:13 am »

you can increase the timing to help with starting on an old tired motor. the exhaust will smell a bit funky, but oh well.

synthetic is definitely the way to go!

Peter · « **Reply #4 on:** September 01, 2007, 12:20:26 pm »

Quote from: "jtanguay"

you can increase the timing to help with starting on an old tired motor. the exhaust will smell a bit funky, but oh well.

synthetic is definitely the way to go!

I have already adjusted the timing and it starts well...But I am more concerned about at "what point" will the compression bye-pass the rings and start shooting oil out of the dip stick pipe...

rallydiesel · « **Reply #5 on:** September 01, 2007, 12:20:55 pm »

If it starts fine and doesn't use a lot of oil than why not leave it? Unless you plan on keeping the car for a while, in which case I would plan a rebuild in the near future.

Peter · « **Reply #6 on:** September 01, 2007, 12:24:55 pm »

Quote from: "Patrick"

Does seem low....... Had one here that was iffy last winter on a bad day with about 420 lbs across all 4. If it starts good in the winter don't worry about it! Maybe the guage is a little off. Got another guage you can screw on the tester?

..just maybe that gauge is out of calibation..new chinese made , harborfreight, cheap price probably equals "junk"..I guess you get what you pay for it

jtanguay · « **Reply #7 on:** September 01, 2007, 02:14:29 pm »

Quote from: "Peter"

Quote from: "Patrick"
Does seem low....... Had one here that was iffy last winter on a bad day with about 420 lbs across all 4. If it starts good in the winter don't worry about it! Maybe the guage is a little off. Got another guage you can screw on the tester?
..just maybe that gauge is out of calibation..new chinese made , harborfreight, cheap price probably equals "junk"..I guess you get what you pay for it

princess auto has some nice gauges that might work.

i would say that in any old diesel, oil will shoot past the rings, unless you re-bore and use new rings (but when the ring gap increases, the oil will shoot out anyways...) high boosting will increase the oil shooting through. thats why you hear non turbo guys talking about super high mileage vs turbo powered diesels. all depends on your driving habits i'd say. go with totalseal rings if you want to minimize oil blowby.

bigblockchev · « **Reply #8 on:** September 01, 2007, 08:15:53 pm »

If the symptoms are not too bad just drive it. When the compression gets low enough to matter you will know it, hard starting, blue smoke out the back, etc maybe even engine runaway due to oil getting past the rings. On the other hand you could do a ring job which is not too expensive and get some more life out of the motor. Just be aware that you will have to deal with what ever you find at the time ie worn bearings & crank, worn out oil pump, leaking seals, worn out oil pump and such. Cheers Dan

Peter · « **Reply #9 on:** September 02, 2007, 11:14:45 am »

Quote from: "bigblockchev"

If the symptoms are not too bad just drive it. When the compression gets low enough to matter you will know it, hard starting, blue smoke out the back, etc maybe even engine runaway due to oil getting past the rings. On the other hand you could do a ring job which is not too expensive and get some more life out of the motor. Just be aware that you will have to deal with what ever you find at the time ie worn bearings & crank, worn out oil pump, leaking seals, worn out oil pump and such. Cheers Dan

so far luckly there are no apparent symptoms other then 2-3L of oil every 600miles/ highway driving..I agree with you that once you tear into the motor for replacing the rings, you might as well at least do the rest of the bottom end..my car still has a near rust free body etc

bigblockchev · « **Reply #10 on:** September 02, 2007, 02:26:26 pm »

If you are only getting 2-300 km/L of oil that is fairly dicey. I would plan on doing at least a ring job in the next few months. Cheers Dan

Peter · « **Reply #11 on:** September 04, 2007, 11:28:07 am »

Quote from: "bigblockchev"

If you are only getting 2-300 km/L of oil that is fairly dicey. I would plan on doing at least a ring job in the next few months. Cheers Dan

...Just maybe the new compression tester may be off calibration a little because after 21yrs of driving vw diesels, and anytime one of my cars would approach 300psi there would be hard starting problems and also when flooring the diesel pedal while standing in the drivway I would have large amounts of black smoke coming out of the tail pipe...this car when completely warmed up shows virtually no black smoke when flooring it, and very hard too see the blue smoke... starts up instanteously both in warm or very cold weather...maybe the high oil usage is a combination of several things like old valve guides/ worn compression rings and perhaps even more importantly,worn out oil control rings (my old '85 with excellent compression sucked oil for years..poor or worn oil control rings)..maybe the high oil consumption is a result of this car having sat for 7 yrs in the garge before I got a hold of it.. I am only guessing here, but maybe this also effected the oil control rings to seize up??

jtanguay · « **Reply #12 on:** September 04, 2007, 01:33:04 pm »

you could always try that oil thickening stuff (also known as stop leak) but beware that you will need to let your car warmup a bit longer. also, dont forget to change oil before you reach sub zero C temps. wynn's helped me a lot in my old diesel. i burnt no oil, and little or no smoke, but come winter time, it was a pain to start, and probably did more bad than good.

bigblockchev · « **Reply #13 on:** September 05, 2007, 08:22:31 pm »

The oil rings have very little tension on them when new so I wouldn't be surprised if they let quite a bit of oil by when they get older/worn. You should be able to substitute any 500-600 psi guage for the one in the tester and get an idea of how accurate it is. Cheers Dan