Expensive automotive borescopes - worth it?

[Stephen Tashiro]

Do expensive automotive borescopes (costing hundreds to thousands of dollars) provide a clear enough view of the inside of a cylinder to see things like small cracks and defects?

I've only used an inexpensive borscope from Harbor Freight to look inside cylinders. I suppose I could tell if a quarter of a valve was missing, but, in my hands, it isn't useful for a refined diagnosis.

For many engines, I'd think that some sort of telescope with ordinary lenses and a light and a mirror on the end would be better than the fiber optic instruments. Did they have instruments like that "in the old days"?

[Joe Angrisani]

What's wrong with a leakdown tester?

[Stephen Tashiro]

What's wrong with a leakdown tester?

As a matter of fact, I've been doing leakdown testing on a 2.5 L "Iron Duke" engine in 1987 S-10. I find that as I increase input pressure , the cylinders (#1 and #2) will only hold about 10 PSI and I suspect the other cylinders would show the same results since they all compression tested at about 90 PSI. I've used a mechanics stethescope to listen for air leaking and I'm not confident of my ability to diagnose the problem that way. There are no bubbles in the radiator during the test. I don't want to start taking the engine apart yet since this is my friend's truck and he has gotten busy with other matters. However, I would like to get the thing out of my driveway before Christmas.

[Jeff Monson]

I dont think a borescope is going to help you out any honestly. We have a good quality one and it hardly gets used. A leakdown tester is your best bet....but if you only have 90psi on all cylinders (if I'm reading your reply correctly?) I'd look at the timing gears.

[Joe Angrisani]

As a matter of fact, I've been doing leakdown testing....and I'm not confident of my ability to diagnose the problem that way.....

Compression test is useless. Get any diagnosis based on one out of your mind. And air bubbles are "too coarse" a test. Listen for the air in a QUIET environment.

ARE YOU 100% POSITIVE YOU ARE ON TOP DEAD CENTER FOR EACH CYLINDER, IN PROPER ORDER, AS YOU TEST??

Hiss at muffler? Exhaust valves.
Remove air filter, hold throttle valve open. Hiss behind airfilter? Intake valves.
Remove coolant cap. Hiss at coolant? Head gasket issue or (unlikely) crack to water jacket.
Remove oil cap. Hiss at oil cap? Rings or head gasket issue or (unlikely) crack to oil passage.

That 90% is going somewhere. You won't miss it.

[Jeff Monson]

Hiss at muffler? Exhaust valves.
Remove air filter, hold throttle valve open. Hiss behind airfilter? Intake valves.
Remove coolant cap. Hiss at coolant? Head gasket issue or (unlikely) crack to water jacket.
Remove oil cap. Hiss at oil cap? Rings or head gasket issue or (unlikely) crack to oil passage.

That 90% is going somewhere. You won't miss it.

Good advice Joe, always works best to stick with the basics first.

[Mike Henderson]

I'm no expert mechanic, but the first thing I'd ask for is the history on the engine. If it's an old tired engine, I'd first suspect that the valves are not sealing well. If the engine has had it's oil changed on a regular basis it's not likely to be rings. If your friend has been using the engine in the past and not losing coolant, I would not suspect the head gasket initially. And I certainly wouldn't initially suspect a cracked cylinder until I ruled everything else out.

As the doctors say, "When you hear hoof beats, thinks horses, not zebras."

Mike

[And if it's burning oil, that would point me towards valves. Rings don't go bad commonly on modern engines but the valve guides wear out and oil starts leaking into the cylinder along the intake valve stem. If the guides are worn out, it means it's been a long time since the valves were done.]

[Stephen Tashiro]

The history of the engine is that my friend rebuilt it in 2007. The fiber-plastic timing gear disintegrated late in 2008, as I recall. We replaced it with an aluminum one. We were getting compression in the 150's in all the cylinders at that time. He did mostly around-town driving. He was doing highway driving at the time of the breakdown. The engine lost power and overheated. Much of the coolant was lost. I've replaced the coolant and see no leaks, so I think it probably was boiled away. Now the truck will crank and I think I hear some combustion, but it won't run.

I'm familiar with the standard advice about how to listen for air leaks and I can hear air in all the places on is supposed to listen for it, except in the radiator. However, whether it is the nature of the leak or my own skill that's at fault, I can't confidently isolate one particular source as the most likely.

My own guess is that it's the head gasket or another failure in the timing gear. Unfortunately, that leads to two very different disassembly strategies!

I'm sure the cylinders were tested with the pistons at top dead center on the compression stroke. By blowing air into the cylinder, I can detect the difference in TDC compression and TDC with a valve open. I get zero PSI in the cylinder when a valve is open. However, I can't see whether the valves are really closed properly at TDC compression. Through the oil fill hole, I can see the valve lifters (or depressors?) on cylinder #1 and if I understood the engine better, I could probably tell whether the valve positions looked right. ( I didn't help rebuild the engine.)

I'm still interested in the borescope question, apart from the particular problems of this engine.

They have dyes one can use to detect leaks in automotive AC systems. I wonder if there is a similar product for cylinder leaks.

[Scott T Smith]

The history of the engine is that my friend rebuilt it in 2007. The fiber-plastic timing gear disintegrated late in 2008, as I recall. We replaced it with an aluminum one. We were getting compression in the 150's in all the cylinders at that time. He did mostly around-town driving. He was doing highway driving at the time of the breakdown. The engine lost power and overheated. Much of the coolant was lost. I've replaced the coolant and see no leaks, so I think it probably was boiled away. Now the truck will crank and I think I hear some combustion, but it won't run.

I'm familiar with the standard advice about how to listen for air leaks and I can hear air in all the places on is supposed to listen for it, except in the radiator. However, whether it is the nature of the leak or my own skill that's at fault, I can't confidently isolate one particular source as the most likely.

My own guess is that it's the head gasket or another failure in the timing gear. Unfortunately, that leads to two very different disassembly strategies!

I'm sure the cylinders were tested with the pistons at top dead center on the compression stroke. By blowing air into the cylinder, I can detect the difference in TDC compression and TDC with a valve open. I get zero PSI in the cylinder when a valve is open. However, I can't see whether the valves are really closed properly at TDC compression. Through the oil fill hole, I can see the valve lifters (or depressors?) on cylinder #1 and if I understood the engine better, I could probably tell whether the valve positions looked right. ( I didn't help rebuild the engine.)

I'm still interested in the borescope question, apart from the particular problems of this engine.

They have dyes one can use to detect leaks in automotive AC systems. I wonder if there is a similar product for cylinder leaks.

Dye's are commonly used to check for cracks (Zyglow), but only when it's disassembled.

When you're running your leakdown test, after taking the "dry" measurement squirt some oil into the cylinder via the spark plug hole, turn it over one time and re-take the test. If the leak down percentage drops, then your problem is the rings.

I'm not sure that I follow the sequence of events... did the overheating problem occur recently, or when the timing gear was replaced 3 years ago?

[Jeff Monson]

I'm still interested in the borescope question, apart from the particular problems of this engine.

They have dyes one can use to detect leaks in automotive AC systems. I wonder if there is a similar product for cylinder leaks.

Stephen, the more expensive borescopes let you see a larger, clearer picture of the cylinder. The one in my shop now has a screen that displays the images, rather than looking into a monoculor like the cheaper ones.
It also has a better, adjustable light source and a good quaility mirror that will give you a good look at the valves. It is a really nice tool to have at times, but as I stated before, it doesnt get used much. I have used a $120.00
scope that had a pretty decent lens and mirror, it did in a pinch, but was still very time consuming to use.

We have used in the past, a chemical that is put into a sample of the coolant from the enigne, it detects co2 presence. Need to have a running engine for this test though.

[Larry Edgerton]

As a matter of fact, I've been doing leakdown testing on a 2.5 L "Iron Duke" engine in 1987 S-10. I find that as I increase input pressure , the cylinders (#1 and #2) will only hold about 10 PSI and I suspect the other cylinders would show the same results since they all compression tested at about 90 PSI. I've used a mechanics stethescope to listen for air leaking and I'm not confident of my ability to diagnose the problem that way. There are no bubbles in the radiator during the test. I don't want to start taking the engine apart yet since this is my friend's truck and he has gotten busy with other matters. However, I would like to get the thing out of my driveway before Christmas.

Pull the plugs in #1 & #2, squirt in some heavy viscosity oil, roll the moror over once by hand and do a leakdown test again. If your readings are higher it the rings/cylinder wall, if they are the same its a valve/head gasket issue.

Larry

[Larry Edgerton]

I have a borescope that I got from SnapOn, and I have checked out a Harbor Freight one someone had. No comparison. But there is no comparison on price either. With the SnapOn you can see some pretty fine detail. I actually bought mine for looking inside walls, but I have looked in a few cylinders and it works well. The Harbor Freight, not so much. I tried looking in a wall with a customers and I could not tell what I was looking at.

Is it worth the money? Not really, but it is a cool toy........;)

Larry

[Stephen Tashiro]

Pull the plugs in #1 & #2, squirt in some heavy viscosity oil, roll the moror over once by hand and do a leakdown test again. If your readings are higher it the rings/cylinder wall, if they are the same its a valve/head gasket issue.

Larry

I already tried that on cylinder #1 using 10-W30. I'll have to try it using gear oil. However, is it likely that all the rings suddenly went bad? I suppose the oil pump could have failed and made everything go bad.

[ray hampton]

all of the rings could go bad at one time but this would be a rare thing, my guess is a blown head gasket

[Joe Angrisani]

all of the rings could go bad at one time but this would be a rare thing, my guess is a blown head gasket

Or a warped head from the known overheating event.

[Scott T Smith]

Or a warped head from the known overheating event.

+1. If you do have to pull the heads, be sure to get them surfaced.

[jason thigpen]

I have a snap on boroscope that is great. i use it all of the time at work. It cost $400, which is well worth it. I once worked on a customers car that had an intermittent pop under the driver seat when braking hard. I finally ran the boroscope down the ac vent in the floor below the driver seat. There was a hotel key that was lodged in the vent. every now and then, it would come loose and slide about two feet and get stuck again. I could clearly see the key slide by with my scope. I could even read the hotels name printed on it.

[ray hampton]

Jason, if the key kept moving then the driver were doing Jackrabbit starts

[Jason Roehl]

+1. If you do have to pull the heads, be sure to get them surfaced.
...and magnafluxed.

Sudden loss of power and coolant does suggest head gasket or cracked head, especially when your compression is very low on two adjacent cylinders.