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Discussion Starter #1
I am rapidly becoming VN750.com’s problem child, so I apologize in advance. I have looked around the site and while there seems to be quite a bit of discussion about oil changes and plug, strainers etc I am am not seeing anything about this...

With nothing else in the hole, no strainer, grommet, washer or spring, the plug spins in freely until it doesn’t with about 1/8th inch to go. I have inspected both male and female threads for burs or cross threading. I have cleaned the threads with a toothbrush, wire brush and a bottle brush. The plug came out without any problem or indication that going back in might be a problem. When it stops up, I can continue with much more torque than what’s called for (14lbs?) but I’m terrified of stripping threads in the crank case. I have tried many times and the plug stops in the same place each time.

Am I missing something?

52781
 

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Try it with the screen, spring, washer, and rubber gasket installed? Although, the gap looks a lot wider than those pieces will take up.

Not sure what's going on there. Definitely don't want stripped threads on the engine case, caps can be found on eBay.
 

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Discussion Starter #3
I have tried it both with all the parts in and all the parts out. This is the first time I have had the plug out but by the looks of the head it appears that it has been rassled with before. At the moment the perfect wrench to fit it would be a 16.37mm.

It could be that because the diameter of the threaded barrel of the plug is so much bigger than the bolt (?) head, any imperfection in the threads causes a larger increase in resistance than what I anticipate. Turn a standard thread 17mm bolt a quarter turn and there is much less surface area of threads working against each other than with this ‘17mm’ plug. It also could be that I’m over thinking this. Time for a beer.
 

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People have a tendency to overtighten these caps, myself included. I learned quick to just snug it and let it go, because they're so hard to break loose. So the 17mm hex can get chewed up.

If you're sure the threads are all ok, does the cap body look bent or stretched? The holes where the screen covers, those look straight and equal?

Do the threads have a knife edge look or are they somewhat squared or blunt?
 

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Can you post a picture of the plug showing the threads? That is a large gap to be sealed by the O-ring. My bike usually requires a new ring (from the Harbor Freight box) every time I change oil but you have a huge gap compared to what I've seen.
 

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It "should" spin in freely until the shoulder hits the case. Can you get a dental mirror in there to look at the case threads?

Can you get a good measure on the space between the unthreaded shaft and the ID of the case bore and see if it's the same on the top/bottom/left/right? I know you said you checked for cross-threaded, but ... shrug
It might be possible to get a better idea of where it's getting hung up if you wrap one layer of plumbers' teflon tape around the threads and see where it gets gouged after carefully threading it up to the point where it binds in order to get a good read.
 

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Discussion Starter #7
Here’s a picture of the threads. I think they look okay.
52799

When I drained the oil the strainer was torn quite badly. After some thought I think the strainer is more about keeping dirt and metal out of the threads of the plug than saving the engine. I realize there is a lot written on here about whether the strainer is or isn’t necessary. I think I will get a new strainer.
52810


So subject to someone with more knowledge than me talking me out of it, I plan on getting a 30mm bolt in the same thread pitch as the plug, cutting some grooves in it and making a thread chaser to very carefully clean up the engine case threads.

Thanks for the help so far.
 

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The threads on the plug do not look bad at all and the O-ring looks like a normal one that is ready to be replaced. As far as the condition of the screen, wow! That sucker has been ravaged. The screen will catch metal particles and I always clean it when I change my oil. However, I have read posts where guys only changed their oil with the bottom drain plug and regular filter. Some did not even know about the screen and side drain until reading about them on this forum

I would replace the screen (although you may be able to “repair” yours with some JB Weld and carb cleaner or solder it if you are good with a propane torch). It is not usually a high stress item. Although yours looks like a dog chewed on it.

Did you have any luck with a dental mirror and pick? The Teflon tape was a good idea also. The plug should not get tight until the O-ring makes contact with the case. That is why the torque is not very much. Was it hard to remove?
 

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The threads on the plug do not look bad at all and the O-ring looks like a normal one that is ready to be replaced. As far as the condition of the screen, wow! That sucker has been ravaged. The screen will catch metal particles and I always clean it when I change my oil. However, I have read posts where guys only changed their oil with the bottom drain plug and regular filter. Some did not even know about the screen and side drain until reading about them on this forum

I would replace the screen (although you may be able to “repair” yours with some JB Weld and carb cleaner or solder it if you are good with a propane torch). It is not usually a high stress item. Although yours looks like a dog chewed on it.

Did you have any luck with a dental mirror and pick? The Teflon tape was a good idea also. The plug should not get tight until the O-ring makes contact with the case. That is why the torque is not very much. Was it hard to remove?
Hi Jimm, so I see you are having a project here instead of those carburetors.

I pulled my side cap and oil strainer off already and they were in great shape just needed light cleaning of the strainer and re-installed no probs.
52832


So the cap was snugged tight before you removed it, and you didn't need to use excess torque to remove it. So it is the right cap to start with? Now it won't go back in. Very mysterious.

The fact that your cap head is so messed up bugs me. It only needs 18Nm (13 ft-lbs) torque don't exceed please! I would replace it for esoterics P/N 11012-1483 $35 eBay but the threads do look just fine so you have a problem inside.

What I do when I want to see inside is to use my mobile phone camera. Set it so the flash is on. Focus on the filter hole in the side of the engine and keep moving closer until you see only the black hole. The flash will take a great hi-res pic of whats inside. Then you can use the photo viewer on your computer to expand it and see whats inside there.

I'll try to find the parts diagram to see whats actually inside the engine case back there, but hope you can get your photo...

Good luck.
 

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Discussion Starter #10
Hi Kontiki. This was the first and only time I have taken the plug out so I was neither paying attention to how hard it was to remove nor anticipating how hard it would be to get back in again. It literally spins in until the last eight of an inch. I have used a dental pick in the threads and there appears to be some burring at one place on the threads.

Because the strainer was trashed I am wondering if metal fragments got lodged in the threads as the oil was draining out and they damaged the thread or became more lodged when I screwed the cap back in.

What’s messing me up at the moment is the timing of Christmas and New Years. I want to make a thread chaser out of a 30mm bolt but a bolt of that size is only available at 5 day a week industrial supply stores who finally open tomorrow.

Great idea idea about the camera. I’ll try that. This is what it looked like when it came out. I’m either missing the grommet or it is attached to the screen.
52833

strainer still in
52834

52835

52836
 

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Yes, the grommet is the black part on the screen in your pics. If it's still soft it can be peeled off the screen.
 

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Yes, the grommet is the black part on the screen in your pics. If it's still soft it can be peeled off the screen.
EDIT: This post is just theorizing, but could be wrong about whether the threading is in the crankcase or not. See Post #19 for picture.

Hmmm Jimm, better hold off on that idea of the 30mm bolt and tapping.

I am very concerned, but the evidence makes me think you have a physical obstruction, not in the threads. This is all hypothetical and I'm still looking for the engine diagrams to show how the oil strainer fits into the side crankcase.

Thoughts:
1. With those big wide coarse threads in the cap, it would usually have no difficulty clearing anything but a massive thread damage when you torque in the cap. The fact that the cap head bolt is so knackered means it has undergone extreme excessive torque, which could have caused damage to the internals.

2. If the cap was snug against the case to begin with, then the damage was increased during the recent removal.

3. Your initial photos look like the cap is threaded into a cylindrical tube that extends from the inner crankcase oil sump area towards the cap hole. The cap is not being threaded into a hole tapped in the crankcase itself. That explains the design of the cap where the threads are on an extended portion of the plug.

4. You need to do physical measurements before you do any tapping of the inner threads. If you have visibility, put your pick in there into the final inside thread. Measure how far it is from there to the side of the case. Then compare to the last cap thread to the underside of the cap head. You will find that the cap appears too long?

5. If the cap screws into an internal cylinder protruding from somewhere inside the engine, and if that cylinder's threading doesn't allow the cap to go in far enough to touch the side of the case, then: The internal cylinder has moved outwards (!!).

These are just thoughts, but evidence points to the inner cylindrical tube that the cap screws into being damaged.

It is scary, so lets stay calm until we are sure of what is physically going on in there.

One other explanation is that the cap plug itself is the wrong one for your bike. You have a 1985 model which was the first of the beasts and did undergo changes. I can't even locate the P/N for 1985. So far I found two versions of cap, for the 750s etc and for the 900/1500 etc. If the previous owner replaced the cap with the wrong (longer) one, and found it wouldn't go all they way in, he could have torqued it massively thus damaging the bolt head and the internal cylindrical tube, which may have moved outward when you recently removed the cap. If possible take yours to the dealer and compare to the right part.

Yes, if the inner tube is intact and in its proper position, then having a blockage in the threads would explain the issue also. But this alternative investigation should be checked before doing any thread chasing. You have already thread-chased with your existing cap plug, and it didn't help. Instead of chasing, you would have to actually tap more deeper threads. Signs are that it is not a thread issue.

Still all hypothetical, just using clues to solve your mystery.

Need better photos and those measurements, and diagrams of the exact internals of the oil strainer inside the crankcase.
 

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There is supposed to be a washer with the screen assembly. It may be broken and a piece obstructing some way. Stick your finger in there and check. That screen is beyond help and is necessary to help keep the oil clean of debris.
 

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Discussion Starter #14
Thanks Spockster. I have the whole thing on order. Part 16097 on Kontiki's pics above. If I could find another grommet about an 8th inch thick, I could button this up!:p

Kontiki, I agree that a home made thread chaser made out of a bolt is a hail Mary. The plug doesn’t suddenly resist turning but quickly builds up a resistance to turning. If both plug and case are aluminum or an alloy that is similar, it’s strange that there is no damage or disfiguration to the plug threads particularly at the inner end. My thread gauge shows a constant pitch of 1.5mm. But the spring that holds the strainer in place is steel.

Here are some measurements which I have included a picture of:

Case:
outer surface to start of threads 16.2mm
outer surface to end of threads 28.8mm
Therefore threaded depth 12.6mm
The diameter of the passage bore only reduces by the depth of the threads once the threads start. There is no change in bore diameter after that.

Plug:
Flange to tip 25.6mm
Depth of threads 10.2mm

When fully screwed in the plug leaves 3.2mm (28.8mm - 25.6mm) of unused thread in the case.(approximately 2 threads as the pitch is 1.5mm.)
52843


The spring and all the other contents associated with the strainer extend into the case threads 10.2mm. (28.8mm-18.6mm)
52845

That means that the plug compresses the spring 7mm (10.2mm-3.2mm).
There is no washer between the spring and plug as per the parts diagram.
The spring is counter clockwise wound.
52844

As the plug screws clockwise against the spring there is an unwinding affect on the spring, increasing the diameter of the spring where the spring and plug contact.
This could possibly cause the end of the spring to bur the threads as the plug is tightened or where the end of the compressed spring comes to rest when the plug had been tightened.(I don't think over tightening would cause this or make it worse...but I think there should be a washer between the plug and spring)

When the plug starts to bind up on something (with spring etc. removed) the flange is 4.9mm from the case surface.
52846

This would indicate that the thread damage starts 8.2mm (4.9mm + 3.2mm) from the end of the threads...within the range of compression of the spring.

I can feel burring at the 8 o'clock position at what feels like 3 threads up from the bottom. At this pitch that would be 4 to 5 mm (3 x 1.5) (I don't know where 8 o'clock is in relation to where the threading starts). 12.6 - 4.5 puts us at 8.1mm...same neighborhood as above.

I'm no CSI guy but this is my theory until it changes.

and maybe...

The spring was put in crooked at some point causing it to jam and damage the threads. The jammed spring did not push against the strainer adequately causing it to flop around in the crank case and tear as it did.

time for a beer
 

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Thanks Spockster. I have the whole thing on order. Part 16097 on Kontiki's pics above. If I could find another grommet about an 8th inch thick, I could button this up!:p

Kontiki, I agree that a home made thread chaser made out of a bolt is a hail Mary. The plug doesn’t suddenly resist turning but quickly builds up a resistance to turning. If both plug and case are aluminum or an alloy that is similar, it’s strange that there is no damage or disfiguration to the plug threads particularly at the inner end. My thread gauge shows a constant pitch of 1.5mm. But the spring that holds the strainer in place is steel.

Here are some measurements which I have included a picture of:

Case:
outer surface to start of threads 16.2mm
outer surface to end of threads 28.8mm
Therefore threaded depth 12.6mm
The diameter of the passage bore only reduces by the depth of the threads once the threads start. There is no change in bore diameter after that.

Plug:
Flange to tip 25.6mm
Depth of threads 10.2mm

When fully screwed in the plug leaves 3.2mm (28.8mm - 25.6mm) of unused thread in the case.(approximately 2 threads as the pitch is 1.5mm.)
View attachment 52843

The spring and all the other contents associated with the strainer extend into the case threads 10.2mm. (28.8mm-18.6mm)
View attachment 52845
That means that the plug compresses the spring 7mm (10.2mm-3.2mm).
There is no washer between the spring and plug as per the parts diagram.
The spring is counter clockwise wound.
View attachment 52844
As the plug screws clockwise against the spring there is an unwinding affect on the spring, increasing the diameter of the spring where the spring and plug contact.
This could possibly cause the end of the spring to bur the threads as the plug is tightened or where the end of the compressed spring comes to rest when the plug had been tightened.(I don't think over tightening would cause this or make it worse...but I think there should be a washer between the plug and spring)

When the plug starts to bind up on something (with spring etc. removed) the flange is 4.9mm from the case surface.
View attachment 52846
This would indicate that the thread damage starts 8.2mm (4.9mm + 3.2mm) from the end of the threads...within the range of compression of the spring.

I can feel burring at the 8 o'clock position at what feels like 3 threads up from the bottom. At this pitch that would be 4 to 5 mm (3 x 1.5) (I don't know where 8 o'clock is in relation to where the threading starts). 12.6 - 4.5 puts us at 8.1mm...same neighborhood as above.

I'm no CSI guy but this is my theory until it changes.

and maybe...

The spring was put in crooked at some point causing it to jam and damage the threads. The jammed spring did not push against the strainer adequately causing it to flop around in the crank case and tear as it did.

time for a beer
Wow, some light reading for tonight...
I'll try to summarize the evidence in the case and see where it leads us now.
MacGyver where are you?
 

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Wow, some light reading for tonight...
I'll try to summarize the evidence in the case and see where it leads us now.
MacGyver where are you?
Go to your friendly dealer and get the correct part, making sure he will take returns. Bring your old one and compare them before you even leave the store.

Try out the new plug. Don't even be concerned with the spring, washer, grommet, strainer at this point, just run the cap in by itself.

You gave another clue: It does not hit a wall, it just gets harder to turn as it goes further in. This is a sign of: Cross-Threading.

Check for that and if so, you can plan the repair.

Make sure you have the visuals (Hi-res photos) so you can verify the threads and any blockages.
 

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Discussion Starter #18
I found this in the oil drain passage downstream from the strainer position but upstream from the threads today. Not sure if this qualifies as a shaving or a chunk. There are likely more of these. I still have the sediment of the oil that came out so I plan on getting down and dirty with that.
52847

I ordered a new plug and priced up a 30x1.5 tap but I think I have done all that I can with the engine in the bike (hole obstructed by the side stand bracket).
 

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Is that chip magnetic? I have been looking through my pictures from working on my and my son's bike and came across this picture of the other side of the drain (when we split the case to fix the broken shift rod). This way you can see what is on the other side of the threads, where the screen goes. Must of the fine particles we ever found were either rubber or fine aluminum or grit from the clutch plates. I would not want to go without the screen even if it doesn't do much. I don't have a extra plug out to measure but the head on your plug looks different from mine.
52848
 
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