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OT- Anyone here instruct me on procedures to inspect Detroit 12V71TA cylinder liners?
- Thread starter Milacron
- Start date
- Replies 16
- Views 2,261
Ziggy2
Stainless
- Joined
- Jun 22, 2013
- Location
- Northern Il
There are six inspection doors per side on the outside of the block. They actually should look more like a small door that is held in place with one bolt.
You can take all of the doors off at once and save some time and effort by bouncing around from side to side and cylinder to cylinder. You should be able to inspect all 12 cylinders with just one rotation of the crank.
As far as a wrench, your best bet would be to probably use a strap wrench. You can rotate the engine either direction without the risk of loosening the harmonic balancer retainer nut.
You can also use a bar on the flywheel ring gear teeth. This would probably give you better positioning accuracy at the expensive of being more tedious.
The three things to look for are rust, scuffs from rings and piston, and possible cracks. The cracks are not always visible early on as they usually start at the bottom of the block bore from being too loose in the bore and migrate upwards to the intake ports.
Liner cracks are the least concern in the inspection. The rust and wall scores are the biggies. The rust usually occurs at the top of the cylinder from an open exhaust valve and the scores are usually just above the intake ports but can also be at the top down.
I was able to turn the crank manually once before by using a 3/4 drive socket wrench on a large nut on one of the pulleys at the end. Seems like I also used an extension pipe on the wrench handle. Worked well as I recall but didn't know if that was the "official" method or not.
Would a straight bore scope work just as well as any or would one that flexes be of any benefit ? Look directly thru glass or LCD screen type ?
Would a straight bore scope work just as well as any or would one that flexes be of any benefit ? Look directly thru glass or LCD screen type ?
I don't know the answer but I offer a comment on video bore scopes in case you need to buy one to perform the inspection.
I much prefer the type where the display module is remote (connected by wire only) from the flex arm/camera. That way you can place the display in a fixed (hands free) position for easy viewing making it much more intuitive to manipulate the camera onto the desired area.
When the display is physically coupled to the flex arm/camera (display screen moving around while trying to orient the camera), I find it a real PITA except in the simplest uses.
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Toms Wheels
Titanium
- Joined
- Dec 30, 2005
- Location
- Jersey Shore
A flexible borescope would be the ticket. The covers are large, but the ports are quite small, each out about 7/16 wide by 7/8" tall. (its been many years since I last looked at a 71) and access under your exhaust manifolds is likely tight.
Expect to see oily crud all over the cavity when you remove the covers, a handful is not uncommon. On marine applications I don't know where the airbox drains go, but there will be two drains per side, 1/4 size hose, drains off the liquid oil from the airbox, leaves the crud behind. Be sure they are not plugged, easy to blow air through them to be sure.
Expect to see oily crud all over the cavity when you remove the covers, a handful is not uncommon. On marine applications I don't know where the airbox drains go, but there will be two drains per side, 1/4 size hose, drains off the liquid oil from the airbox, leaves the crud behind. Be sure they are not plugged, easy to blow air through them to be sure.
I can relate as I have one of those cheap LCD screen scopes like one buys at Home Depot and it is indeed a PITA to have to keep the LCD screen in proper orientation " to see what you need to see" in combination with the flex scope movements. Regardless, it has been quite useful in tight wiring runs on the boat, but I can see how a separate stationary monitor would be even better indeed.
Winmac
Aluminum
- Joined
- Dec 9, 2011
- Location
- Cape Breton, Canada
If it's something you will need to do often, there is a turning tool. Mounts in the spare starter mounting hole and allows you to use a 1/2 drive ratchet to turn engine.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Glad to here yours was cheap. I think I spent over $300 for my Milwaukee POS to learn that lesson.
These days there are many better and less expensive options. Such as . . .
Amazon.com: Wireless Endoscope, Depstech WiFi Borescope Inspection Camera 2. Megapixels HD Snake Camera for Android and IOS Smartphone, iPhone, Samsung, Tablet - Black(3.5 Meter): Industrial & Scientific
Seems like mine is the "Rigid" brand, maybe 100 bucks on sale...which sounded dirt cheap at the time considering the pretty clear color screen and all. But it is a PITA sometimes as one basically is having to make two bends at once to see the little screen properly...one bend of the "camera" and then the opposite bend at the monitor to orient the screen back to optimal viewing.
Have you actually tried the one you link to ? Wondering if the image quality is similar to the image quality of the smartphone or tablet....i.e. does one have "retina screen" quality view of the bore if using a retina screen iPad for example ?
Plus there would be the advantage of keeping the images as a jpeg or video file in the device...for later viewing, image size increase, or email or whatever.
No, I haven't used the one I linked to. Just an example. Actually I haven't bought a new flexible borescope type.
However, I have bought the one linked below and been very pleased. It's not 'flexible' so maybe not acceptable for your inspection.
It's about .5" diameter so can get into fairly tight places and focusable (I think most borescopes are fixed focal length). I keep it connected to a tired old lap top.
5 x 8 LED 2 MP USB Digital Microscope Video Webcam Magnifier Camera Stand | eBay
I found mine yesterday. On 1993 vintage Detroit 12V71TA, the inspection covers are held in place by two bolts..... except the two most forward cylinders on each side are one longer cover that covers two cylinders, held by three bolts ! No clue why they did it that way.
Yesterday I saw on of the cylinder inspection holes for the first time, and now realize once the view end is inserted, I need to be able to see 360 degrees, up and down. Which means I need a "steerable head" type.....which I feared means big bucks.....but the below eBay one is surprisingly cheap. I wonder how easy it would be to "articulate" the head compared to the $8,000 types however....may start another thread just on articulating bore scopes.
Vividia AbleScope VA-4 HD USB Borescope with 18deg Articulating 8.5mm Probe | eBay
It's fascinating that out of over 200 feedbacks, the few neutral and negative feedbacks concern shipping issues.....everyone seems satisfied with the operation and image quality.
. . . and the seller's in your neck of the woods.
I see that you linked to the scope with the rigid extension, not the flexible one.
Both have articulating tips but don't forget about the fixed focal length. You'll need to get the camera the correct distance from the subject, not just pointed at the subject. Will you have sufficient access clearance to achieve both focal distance and orientation with the rigid extension?
I see that you linked to the scope with the rigid extension, not the flexible one.
Both have articulating tips but don't forget about the fixed focal length. You'll need to get the camera the correct distance from the subject, not just pointed at the subject. Will you have sufficient access clearance to achieve both focal distance and orientation with the rigid extension?
Yeah I thought about that a few hours after I posted the link. I'd prefer the straight one if it was shorter but come to think of it, the acessable inspection covers for the starboard engine are on the side between them and the hull, in which case the straight scope might be too long. But if they made one about 1/3 that long I would still be inclined to go with the straight one.
for the heck of it I bought a few different sizes of this scope from China for twelve bucks:
1mm Lens 4 LED 5M USB HD 72P Endoscope Borescope Tube Inspection Video
I was shocked at how good it worked. They come in different diameters, I got 5.5 and 8mm. I've linked to the 10 because the 8 was MUCH better than the 5.5 so I figure the 10 would be better still. The built in leds are not great, but if you can augment it with a mini high power led flashlight the image is REALLY good. The ones I have have a little flip up section on the usb connector so it will connect directly to an android phone- I don't see that on this 10mm one I linked, but you can search for one that has it. It also asked you to download their app from some other location than the google play store- I wasn't about to do that for security reasons but the "scopecam" app on the play store works fine
1mm Lens 4 LED 5M USB HD 72P Endoscope Borescope Tube Inspection Video
I was shocked at how good it worked. They come in different diameters, I got 5.5 and 8mm. I've linked to the 10 because the 8 was MUCH better than the 5.5 so I figure the 10 would be better still. The built in leds are not great, but if you can augment it with a mini high power led flashlight the image is REALLY good. The ones I have have a little flip up section on the usb connector so it will connect directly to an android phone- I don't see that on this 10mm one I linked, but you can search for one that has it. It also asked you to download their app from some other location than the google play store- I wasn't about to do that for security reasons but the "scopecam" app on the play store works fine
Drillrigdoc
Plastic
- Joined
- Jul 20, 2015
Those borescopes are really trick but I've inspected many a Detroit without one. Anything good or bad can be seen through the ports in the liner. You'll also want to look at the rings as they pass by the ports, it's handy to have a strong youngster along to bar the engine for you. Also would be a good time to go through the tune up. Don't forget to look for excessive oil in the cylinders at bottom dead center. If the engine has oil ring problems it can get expensive.
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Yes, there seems to be 3 rings per cylinder. Re "bar the engine" I have turned them over before with a 3/4" ratchet on the 1.5" nuts on the front pulleys with a 2 foot extension and don't recall it being all that difficult. It would be nice to have a helper though just to shout "ok, stop" when piston at bottom.
