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I've got an oil leak, can you help me diagnose the source?

8K views 32 replies 4 participants last post by  bigolepit 
#1 ·
Hi folks,

I've got a 1983 VT750 and I've got an oil leak that appears like it should be fixed before spring riding season.

I had some trouble trying to describe where it stems from, as my technical language around mechanics is .. non-existent, really. So to make up for that, I put together a quick video that gives you a clear idea of the origin and extent of the oil leak(s):



Have any of you Shadow owners with older bikes experienced this? If so, what was the cause the solution in your case? Was it necessary to remove the engine and do a full replacement of gaskets, or is it something simpler like an O-ring that needs replacement?

Thanks in advance!

Vlado
 
#2 ·
That is a plug there is no oring in that spot. It does not just pop out, atleast it's not intended to. To replace it you have to take those top pieces off the bike. Mine used to slightly leak, when I did my rebuild I just used some silicone to seal them up. You should be able to get a new one if you want but I'm thinking your not going to have room to take it apart in the frame.

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#3 · (Edited)
#4 ·
I used black oil resistant gasket silicone. It's held up just fine. If you use silicone rather than replacing the plug just wipe off the excess that squeeze out after you tighten it all down and no one will be able to tell the difference.

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#6 ·
Thanks Bigolepit, I found the silicone stuff at my local Canadian Tire and will do some oil cleanup before applying it to the plugs. I'll report back with progress. Hopefully there's a warm enough day to turn it on and see if it holds :)
 
#7 ·
It is a common problem on these older bikes. Mine were seeping a little when I got it from a friend and then I put in Synthetic oil and it made it worse, seems that synthetic will clean out any gummed up residue that was keeping the oil from seeping out of gasket joints. I tried to seal it from the outside and it work for a very short time. You can't stop oil from seeping through a seam very well after it has made a channel. To take it apart plan for a top end overhaul however, with all the gaskets.
Here is a photo of what the rubber plug seal and head looks like.
 

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#8 ·
Thanks for the pictures, Swifty! It certainly helps to see what I'm looking for inside. I'm hoping the silicone seal holds up this year, then I can plan for a rebuild starting early winter and giving myself ample time to do it.
 
#9 ·
Mine doesn't leak as bad as yours so I am putting off tearing into it. I hate to take apart an engine if it is running good and no other problems. If you are willing to experiment, here is a though I had considered. The holes are 22 MM so a 7/8 inch expanding rubber plug would be able to seal it well without engine disassembly.
It looks like the factory plugs have a metal body with rubber coating. So they may pull out with a hole drilled in the center and a screw into that, just like taking out the carb mixture screw plugs. After the bore is cleaned out an expanding rubber plug could stop the leak. It may sound a bit "mickey mouse" but it would sure save a lot of money and time. What do you think?


7/8" Rubber Expansion Plug/Rubber Freeze Plug/ Exhaust Pressure Test Plug/ | eBay

0.875 inch wing nut action neoprene rubber stainless steel expansion test plug
 
#10 ·
Can always count you @swifty2014 for good pics of a repair lol. I didn't put silicone on the outside of mine to be clear, when I had it apart I put the silicone on the radius of the plug as if It was a gasket. It's better to replace them if you can but I haven't had any leaks from it since then.

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#11 ·
That is the way to seal an oil leak, from the inside. Even if you just add silicone to the cleaned old part it usually works fine. An old German master mechanic told me that years ago when he explained why my "goop up the outside" idea, would not work.
I am just curious about those expanding rubber plugs that would make a clean tight fit inside the bore of the head. Just pondering. :grin:
 
#12 ·
@swifty2014, the plug idea intrigues me. From what I can tell, these should be able to withstand high temperatures and pressure. In theory, as long as I can get them in there, they should work.

I guess the details of the removal of existing plugs, with engine in-frame, is the challenge. And not getting bits of the old plugs left inside the engine as well. :S

@bigolepit, I was under the impression that the gasket maker was sticky enough to form a seal around the outside. Oops! I picked some up anyway, it'll come in handy sooner or later. It sounds like I will need to rip out the engine in either case, but can likely get away with using the existing plugs with the gasket maker goop like you did.

I also noticed in the manual that it said that once I remove the engine cap and expose the delicious insides, that I should be replacing some sort of gasket that sits between the cap and the part below it. Did you reuse your existing gaskets there and ass some goop, or did you get new ones? I found a few kits for a complete rebuild up to $100.
 
#13 ·
I stoped my leaky plug at the same time I rebuilt the topend so I had all new gaskets from the base gasket up in the topend kit I bought. If you don't need to do a rebuild then deffinatly get the gasket new even if you have to cut one yourself, I've never had luck with used gaskets and there cheap to buy. You can buy just the one you need rather than the whole kit if that's the only one you need.

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#15 ·
#16 ·
The used gasket issue is one of the reasons I try to avoid taking things apart unless absolutely needed. Any time you take the squeeze off a head gasket and the cylinder gets any movement I would worry about it not sealing as it had been. The bottom gasket also. Maybe I just worry too much.

There won't be any pressure in that area just splash oil.

It seems they are about 3/8 inch deep so I think you could drill in the center and get a screw into it and pry against the side of the head and rip it out. There is a small ridge of rubber inside but it should tear off and be cleaned out. Since it is old and has been leaking it probably isn't fitting too tight anymore.

I even thought of a small slide hammer that I have similar to this.

Slammer Hammer vise grip Puller made for Snap on, Mac craftsman size (SM) | eBay
 
#20 ·
I don't see why an expanding type freeze plug wouldn't work if you can get the right size. I've put them in three or four auto engine blocks and never heard of them failing. The bike would be less pressure. After a couple years if the oil gets to them , just do it again. >:)
 
#19 ·
OK one more wild and crazy idea! If the cams are hollow as they look, after one side is unplugged a guy might be able to run a steel rod all the way through to the other side and just tap the other side plug out. Since bigolepit has had hands on with the cams maybe he can verify if they are hollow as the look.
 

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#21 ·
Unfortunately they are not, just the ends are. As far as the poping the plugs out I personally wouldn't try it. Im not saying it wouldn't work out just fine, it would just worry about reinstall of the new plugs that way might damage the new seal and be right back in the same boat with less cash. I would recommend taking the time to do it right one time. If I'm remembering correctly there is no gasket there just a silicone seal there and a gasket under the cover that holds the assist springs in place that doesn't need to be distributed. The only gasket you should need is for the timing chain cover and shouldn't cost more than $10-15 bucks. Being the front cylinder I'm pretty sure if you take your coil mount off and the 2 coolant tubes off you'll have room to do the job, just watch the lifters and shims they tend to stick in the top section when you pull it up.

This should be the only gasket you will need the other gasket above that plug is for a cover that don't need unbolted so it wouldn't be distributed

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#22 ·
Thanks folks for all the love and advice thus far, I really really appreciate it! :)
@swifty2014 I'm liking this plug idea more and more. I still have concerns about getting the plugs out in the first place without leaving remnants of plastic/rubber inside the chamber as I attempt to get the plug out. If I can figure out a clean way, I'm willing to try it out. If anything, for the experience of doing it.
@Sundown have you had experience removing existing plugs like the one in my engine? If so, how did you go about doing it in a clean way?
@bigolepit Unfortunately it's both the front and rear cylinder, and both sides on both.. so all 4 plugs are leaking. I would imagine the whole top's gonna have to come off, and the engine's gotta come out for that. I think there's a couple more gaskets to go along with the one you suggested, but it certainly helps knowing I can do this repair for very little money :)

I'm torn between doing the right thing, and a short term fix. I'm debating trying out the goop around the outside and seeing if it can hold up a couple thousand km this season. If it does, then that buys me time to get the parts I need, prep my workshop for the job, and get to next winter. Then I have all of next winter to rebuild the engine and work on some other parts of the bike.

To be honest, I'm not afraid of the work, but I am highly anxious about the level of complexity that comes with the engine removal. Just looking at the procedure in the Clymer manual of all the things that have to disconnect/be removed with their own complex procedures made my head spin a little bit. I would prefer to do the proper replacement as it gives me a chance to restore the aluminium on the engine heads and get the cosmetics done as well. What does concern me is how many procedures mention "you will need a new seal for this step". Perhaps mapping out the entire process on paper and getting familiar with the parts mentioned will give me a bit more starting confidence so I can get rolling :)
 
#28 ·
@Sundown have you had experience removing existing plugs like the one in my engine? If so, how did you go about doing it in a clean way?

No @vlado , I haven't done any of that on a bike , but on cars there are "freeze plugs" in the block designed to blow out if the engine freezes. On older cars they sometimes rust out. To replace them there are two kinds , one that you tap in with a rubber mallet and a round dowel about 2-2/12" in diameter.

The other style to replace them is based on expanding it once in place with a ratchet to get a snug fit. They work well , and I've never had to replace one twice in the same place.

What I'm not sure of is if you can get the right size. Should be easy to find out on line. Just measure your hole diameter and google replacement freeze plug and that measurement. If you get the right size I'm sure it will get you through the summer.
On the block of a car it is to hold in the same water that is in the radiator and that has more heat and pressure than what you are trying to block. The rubber may be affected by the oil , but I don't think it will melt very fast.
 
#23 ·
If it's all four plugs leaking then your right the engine needs to come out. That's not a hard task to get it out just anoying to do for such a minor issue. Even so you won't need a full topend kit unless your going to take it down to the crankcase which would give you a chance to check for hidden wear and tear that might need attention as you already implied. That's up to you though. A complete topend rebuild does make a good winter project and if you feel it's appropriate then go for it, it can't hurt anything if you do it right.

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#24 ·
Thanks bigolepit for the explanation. You have the experience with the engine top end rebuild so you are the best source. I always feel timid about suggesting an easy fix, but it is good also for the guy who doesn't have experience or the money to rebuild the engine. So if an economical way is found that works very well for a long time, with no "collateral damage", I am eager to know it. And if it doesn't work, then a complete job can still be done.

vlado here are some factory manuals the good folks here have provided. Study it well and know your bike.
http://www.hondashadow.net/forum/72-technical-discussion/122857-honda-service-manuals.html

Here is a video of a guy putting the cam back in, and it helps see the areas and the spaces around the plug areas for reference.

 
#27 ·
Thanks bigolepit for the explanation. You have the experience with the engine top end rebuild so you are the best source. I always feel timid about suggesting an easy fix, but it is good also for the guy who doesn't have experience or the money to rebuild the engine. So if an economical way is found that works very well for a long time, with no "collateral damage", I am eager to know it. And if it doesn't work, then a complete job can still be done.

vlado here are some factory manuals the good folks here have provided. Study it well and know your bike.
http://www.hondashadow.net/forum/72-technical-discussion/122857-honda-service-manuals.html

Here is a video of a guy putting the cam back in, and it helps see the areas and the spaces around the plug areas for reference.

https://www.youtube.com/watch?v=R9WRepdi3ZE
@swifty2014 you give me more credit than I deserve man lol. I do have the hands on experience with this engine but I'm like you if there's a easy cheaper way with no ill side effects I say go for it. I don't want to discourage anyone from looking at other options. And that video was a great post wish I saw that before I did mine I figured it out the hard way lol.

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#26 ·
I love having that manual for knowledge.
As I always say= "Study the manual because there WILL be a test".
 
#29 ·
Our area is being hit with an unusual warmth spell, so I took the opportunity to attempt a temporary hick repair.

I figured if this works, I can properly prepared for a rebuild next winter. I simply applied the high temp silicone around the plugs and did a bit of riding to see how it holds up. Well, it turns out it's holding up very well. Looks like a complete hack job but it might give me a season of riding :)

Here's a quick video so you can see just how goopy it looks.

 
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