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Is it ok to plug in battery backward to do compression test?

This engine is equipped with a voltage regulator. Depending on the exact construction of the regulator a reverse current would be disastrous, especially the high current from a starter battery
Martin's user avatar
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9 votes

Is it ok to plug in battery backward to do compression test?

Why not just put a wrench on the crankshaft? Ignoring the electrical repercussions, I fear damage to the starter, too. Besides, if the starter on this tractor uses a sprag clutch (and probably most ...
justinm410's user avatar
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8 votes

Is it ok to plug in battery backward to do compression test?

Looks like the starter drive is the typical spring loaded drive gear that engages when the starter motor turns in the "forward" direction, then disengages if the engine starts running and overdrives ...
Johnny's user avatar
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6 votes

In Cylinder Pressure Testing With a Pressure Transducer and a Oscilliscope

I use pressure transducers to test for cam sync problems. And other problems. Cam sync problems are seen on the waveform in a section called the exhaust ramp. The middle of the ramp moves back and ...
Fred Wilson's user avatar
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5 votes

Is it ok to plug in battery backward to do compression test?

Even if there are no polarity-sensitive electronics to damage and the starter motor was able to engage, it is unlikely that the motor would rotate backwards anyway. Most car starter motors (in fact ...
nnxen's user avatar
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5 votes

Diesel runaway - stopped miraculously by itself

I'm not familiar with your engine, but on the VW TDI engines quite a bit of oil can accumulate in the intake, particularly in the intercooler. The last time I did the timing belt I found about 100 CC ...
dlu's user avatar
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5 votes

Diesel runaway - stopped miraculously by itself

Regarding loss of compression The loss of compression can be explained by the evidence of oil in the cooling system. The usual way the two fluids mix is when there is head gasket failure and/or ...
Zaid's user avatar
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5 votes
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If an engine starts does that mean compression is fine?

You cannot assume just because it starts it has good compression. It can have minimal compression and still start and run just fine. That minimal compression is going to be different for every engine, ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
5 votes
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In Cylinder Pressure Testing With a Pressure Transducer and a Oscilliscope

Analysing in cylinder pressure waveform is extremely useful in developing combustion strategies in OEM R&D environments and also for diagnosing lots of issues. I have taken picture and its ...
Vish_evo's user avatar
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5 votes
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Used Car Condition - Is a Compression Test a good proxy of engine health? (and what's a leak down test?)

A compression test will only give you a general idea of engine health It WILL NOT help you to understand if there is gunk buildup in the engine It WILL NOT tell you if you have a specific issue with ...
DucatiKiller's user avatar
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4 votes

Used Car Condition - Is a Compression Test a good proxy of engine health? (and what's a leak down test?)

It is good to check first if the coolant in the radiator has oil droplets inside, and if the oil (most of the times using the dipstick) has water inside. Then with a compression test you will be ...
Alimba's user avatar
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4 votes

In Cylinder Pressure Testing With a Pressure Transducer and a Oscilliscope

Most accurate way to diagnose plugged exhaust (not severe) or chain stretch is to compare to known good waveforms on same engine and year. Like any other diagnostic tool of this type it takes time and ...
Moab's user avatar
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3 votes

Where in a Haynes manual would the compression figures be for my engine?

It should be at the beginning of the Chapter 2 portion which covers General engine overhaul procedures. Whether it's in 2B or 2C or subsequent sub-chapters will depend on how many engine options there ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
3 votes
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How to leak down test a cold engine?

So searching the Internet, I've found some conflicting opinions, with an occasional person saying either that cold leak down tests are completely invalid, or that cold numbers will be two to three ...
Robert S. Barnes's user avatar
2 votes

Low compression on all cylinders - Flooded Engine - Maybe Washed Cylinders?

If you attempted to run the engine with the valve train improperly aligned, you may have caused valve damage to your head, as this is an interference motor. This would definitely affect your ability ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
2 votes

Low compression on all cylinders - Flooded Engine - Maybe Washed Cylinders?

Does my hypothesis sound reasonable? What doesn't sit well with me is that the engine has already been cranked a lot (when the cylinders were flooded). Regardless of whether the engine started, ...
Zaid's user avatar
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2 votes
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Low compression on all cylinders - Flooded Engine - Maybe Washed Cylinders?

A teaspoon of oil is sufficient, but this trick does not work if the pistons are dished... the small amount of oil won’t be a problem, it will fall down / burn away.
Solar Mike's user avatar
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2 votes

Are compression tests neccessary?

Compression tests certainly have their uses - I wouldn't go so far as to say they should be a routine part of the car buying process, unless you have reasons to suspect an issue or you're buying an RX-...
motosubatsu's user avatar
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2 votes
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How to interpret slightly varying compression between cylinders?

The smoky exhaust is more often due to oil passing by the worn valve seals and guides. Those readings don’t seem too serious, may cause a slightly rough idle but predicting the further life is just a ...
Solar Mike's user avatar
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1 vote

Are compression tests neccessary?

A compression test is a useful diagnostic aid. It's definitely wrong that all compression-related issues manifest themselves as something that can be seen or heard. It's very possible to have low ...
masospaghetti's user avatar
1 vote

Does substantially increased compression test numbers after adding oil to the cylinder necessarily imply that piston rings and/or cylinder bore is bad

Your compression numbers are at the low end of passable which the book shows to be 145 psi. With new rings, I would expect better. You will almost always see an increase in cylinder pressure after ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
1 vote

Does substantially increased compression test numbers after adding oil to the cylinder necessarily imply that piston rings and/or cylinder bore is bad

The compression looks ok to me. Burning oil could come from the valve stem seals not sealing properly anymore or a blown head gausket. You can check the stem seals by letting the car roll downhill for ...
Pille's user avatar
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1 vote

Compression testing a 2-stroke boat motor

As is said here 2-Stroke Squish & Compression Testing The Best Way to get a Valid Compression Reading A) Within 5 days of a normal “operating cycle - Engines that have sat for a long time may ...
5n10m's user avatar
  • 50
1 vote

Replaced Head on Propane Engine; Now I have too high compression. Why?

This is only a partial answer: You could narrow down your diagnosis by comparing the volume of both heads. If both volumes match, then the new head is fine and your problem lies somewhere else. How to ...
Martin's user avatar
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1 vote

What would cause the two middle cylinders on my v6 to have no compression and the other four cylinders do?

This could be caused by any number of problems. The most common are probably: Stuck or burned valves Blown head gasket Burned piston Damaged piston rings and/or cylinder wall Is there any other ...
jwh20's user avatar
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1 vote

Are compression tests neccessary?

Both are wrong. One cylinder can be down on power without causing excessive noise or vibration, which is why, when you asked the question the other day, I pointed you towards a Morse test. A Morse ...
Solar Mike's user avatar
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1 vote
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Engine Burned Oil | Trying to Diagnose with Compression Meter

It's not that likely to be the head gasket, if it is you'd have oil leaking into the coolant or vice versa, plus lots of white smoke coming out of your exhaust. More likely it's worn rings or your ...
GdD's user avatar
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1 vote

Used Car Condition - Is a Compression Test a good proxy of engine health? (and what's a leak down test?)

A compression test is a proxy for "there's a problem" but you'll probably need to go and do a leak down test to identify specifically what's the problem. As stated above these tools are helpful in ...
eAndy's user avatar
  • 163
1 vote

Diesel runaway - stopped miraculously by itself

I have owned many VW diesel cars since 1977. Runaway in the IDI engines was more common than in the TDI engines. In general, runaway is from the ingestion of oil, normally pooled in the intake ...
mongo's user avatar
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1 vote

More In Cylinder Pressure Testing Questions

I did some searching on IATN and found known good pressure waveforms that are identical to my after repair captures. Unfortunately I can't post them here. It turns out that hump is completely normal. ...
Ben's user avatar
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