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Discussion Starter #1
Hi All,
Have been bothered by an irregular oil leak from the front of the cylinder head. Shows up after a ride as oil blown back around the head on the head fins. I always thought that it was the PRT seals going. However, it does not leak everyride. After a ride on Saturday, I had the oil trail in evidence. So, I cleaned the oil off and rode the bike to work and back today. Looking at bike after this, I would say the oil appears to be coming down the two outer rocker box studs. These are the short studs that hold the front of the exhaust rocker box to the head. The nut screws on from below.
Has anyone seen a leak from here before? I am assuming that the hole in the rocker box that receives the stud is a through hole, and that the oil is finding its way down the threads. if this is the case, what is the best way to stop the oil? Use a suitable thread sealer, loctite 243?
All the best,
Andy
 

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Andy


While I haven't seen this specific leak I have experienced leaks of a similar style. That is oil wicking down or up threaded fastners.


Without having a rocker box in front of me I do not remember if the stud goes into a blind or thru hole. As oil is leaking down the stud I am going to assume it is a thru hole. As such my choice of sealer on the stud would be Hylomar. A second choice would be a bit of Ulta-Grey (Yamabond, Three Bond, grey RTV's). Loctite 243 or 242 are a blue thread sealant and while use on the nut/stud joint is desirable My personal choice would be something to seal the leak where stud thread goes thru the rocker box.


K
 

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Hi Andy,

oil appears to be coming down the two outer rocker box studs. These are the short studs that hold the front of the exhaust rocker box to the head.
the hole in the rocker box that receives the stud is a through hole, and that the oil is finding its way down the threads.
The rocker-box is only the top of the compartment containing the valves, the lower part's in the head and the two parts are sealed by the gasket; it could just be a leaky gasket allowing oil to reach the studs where they pass through ... have you tested the nuts with a spanner, to see if they're tight or they'll take a little tweak?

cleaned the oil off and rode the bike to work and back today. Looking at bike after this,
A quicker test/result might be the 'talcum powder' one. If you haven't heard of this before: thoroughly wash off all previously-leaked oil; allow all surfaces to dry completely; sprinkle or puff talcum powder over and around the suspect area; start engine and observe the suspect area for a period; any leaking oil will spread rapidly through the talcum powder. :thumb If it doesn't leak visibly at a standstill, go for a ride but relatively-slowly (so the talc isn't all blown off) and stop frequently to see the first signs of the leak.

Hth.

Regards,
 

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Discussion Starter #4
Hi all,

In reply to Stuart: Thanks for suggestion with the talc, certainly worth a try out. I did try the nuts, the outer two took a small nip, probably no more than one flat of the hex. The centre nut did not move. So, will observe after next ride and see if that is all it takes!

All the best,

Andy
 

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Hi Andy,
It could be as Stuart advises, a damaged gasket.
There are 3 studs coming down from the rocker box, the middle one is the only one that has a blind hole, the outer two have holes drilled all the way through the rocker box. This immediately gives a problem as studs were not meant to be used in through holes.
I cannot see a way around having the rocker boxes off to solve this if the oil is seeping down the studs.
With the rocker box off the bike:
The middle stud should be tightened in it’s hole until it bottoms out, the resulting pressure pushes up against the whole length of the thread locking the stud in place using the entire length of the thread in the rocker box. When correctly fitted there should be 1/2 to 1 turn of thread showing above the rocker box face.
If you can tighten the stud until all of the threads disappear then the stud will jamb only at one point, where the thread runs out. This puts the entire load concentrated at this point which is close to the rocker box gasket face. There is a likelihood that this concentrated pressure close to the surface will pull the metal up causing a distorted gasket face.

If you double nut the stud(s) and remove it, you can check the gasket face for flatness, and reface it if necessary.

Because it is difficult to tap a blind hole all of the way to the botdtom, there is a chance that the stud will jamb Where the tapped thread in the rocker box runs out above the bottom of the hole. While not as bad as jamming at the top, it still makes for a weak fixing as the forces are concentrated at the jamming point in the bottom of the hole, the rest of the length of thread is effectively ‘loose’.
To overcome the chance of this happening I remove the first turn of thread at the end of the stud. The stud will then press against the bottom of the hole, loading the entire length of thread evenly, making a strong and secure fixing.

The outer two holes have a real problem, there is no bottom of the hole for them to push against as they are drilled right through. The stud will definitely jamb near the gasket surface when the thread runs out, the rest of the thread is then effectively loose, perfect for allowing oil to work it’s way down.
The solution to this is to fit the outer two studs with Loctite 270 studlock.
Clean the head and stud of all oil, coat the stud with loctite 270 and screw the stud in gently until it just starts to tighten, do not pull it down hard. In reality you have glued the stud in place rather than locked it in place. The resulting installation should not allow oil down the threads as loctite 270 is a very effective sealant.
If you ever need to remove the stud again, you will need to heat the stud to release the loctites grip. Trying to remove the stud without heating is likely to rip the threads out of the rockerbox.

Regards
Peg.

+1 on the talcum powder trick (someone also has posted that powdered aerosol foot spray was easier to apply).

Here are some photos showing the poorly designed stud holes drilled all of the way through the rocker box:
 

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Hi AndyT140, Yes they go through to the oil space on my '73 Tiger as well as the ones Peg was nice enough to photo.

I've seen these leak. What I do is use a sealant on both sides of washer & threads of nut. I always use Mercedes Benz
001 989 98 20 10 it is a Loctite product only sold through Mercedes dealers.

It is very similar to Loctite 574. Clean area perfectly to bone dry. Gas or a parts wash or acetone. Dry well. Smear on sealant. Install washer & nut. Torque as you normally would. Let cure 24 hrs. If this is the leak, it will not leak now. Does not seal if parts are oily at all!! Wipe off squish out immediately after torqueing.

Then rode test & evaluate leaks. If gasket is leaking also then you need a full box reseal, including the studs. But if it's just the nut where oil gathers this will fix it. Certainly worth a try.

This sealant will work on leaky cyl base nuts as well. I've done dozens to good results. Only do 1 nut at a time.

This sealant is really good for cly base gaskets & covseal rocker box gaskets. It will really stop leaks.

It also works well to glue studs into case such as the 4 cyl base studs & your rocker box studs. Loctite 243 works well here too. Both can be removed with wrench no heating. Heating with heat gun or the like will melt sealant or 242/243 & fastener will remove easier.

When removing boxes or cyl the gaskets will have to be scraped with a razor blade or the like. Pretty much need to do that anyway.

I always grease both sides of valve cover gaskets so they come off easy & often no scraping needed at all.

Both the Mercedes & Loctite sealants are made for metal to metal no gasket use. If you used these for say timing cover it would be very very hard to remove. It's not recommended for gaskets, but at work we used if for 30+ years to perfect results. The gaskets break apart on removal so not to hard.

For metal to metal like timing cover or case halves hard to beat Loctite 518. No leaks, long working time, easy to separate later. But 518 has proved not very effective with gaskets & can allow them to migrate or split. Cures to a softer plastic.

While 574 will permeate the gasket & make it stable & seal well as it cures to a tough plastic like material.

These sealants will assure a no leak motor. Others work too, but I've found these effective & very easy to use.
Don
 

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Note, there was a suggestion earlier (now removed) that these bikes have rocker oil feed banjos. My T140e is a little newer than yours but I think we share the same rocker feeds (I believe all 650 and 750s are the same but may be wrong) and these do not have banjos. I presume Stuart was talking about triples or the older 500cc engines?

So, just in case anyone was thinking about fixing oil leaks by replacing banjo bolts: The end of the rocker shaft extends outside the rocker box and the oil feed pipe is sealed around it with a couple of washers (one each side of the oil feed pipe), clamped by a nut. It is quite possible that these can leak and I have had such a leak which took a little while to identify as oil travels well on a hot engine and makes it seem that the leak origin lies elsewhere. In my case, it turned out to be a slightly loose nut but I replaced the washers and whilst it was apart, sprayed through the feed pipes with carb cleaner (quite a bit of crap came out too).

For info, the part numbers (in my T140e book) are:
Feed pipe (x1) 71-3550
Nuts (x2) 21-0550
Washer (x4) 70-1335

P.S. I really like the talcum powder technique Stuart, but have a question: is it easy to clean off a talcum/oil mix paste after cooking on a hot engine, e.g. between the cooling fins?

Cheers,
Ian
 

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Discussion Starter #8
Hi all,
Thank you all for all the responses and suggestions above. Managed to get out and do a steady 30 miles or so. Got back and have a few drips of oil coming off the fins. Having cleaned all up earlier, I can see:

1) Drive side outer exhaust rocker box stud has oil coming down the threads.

2) Can also see oil that has been blown around the top cylinder (jug) fin on both sides of the cyilnders.

So, am I safe to assume that:

1) Is oil coming down the rocker box stud. Can try Don's suggestion to use Loctite 574 on washer and nut to do a quick solution.

2) This can only be from exhaust PRT seal?

All the best,

Andy
 

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Hi Andy, The leak around fins might be PRT seals as they are prone to leaks. Could also be seeping head gasket.

I would consider sealing stud nut/washer. Then verify that's fixed.

Then go after the other leak. That can be really hard to diagnose & may take several cleanings. The thing is oil blown by the wind can travel fast & far. Be almost invisible until it droplets. Start with very short road test of only a mile or less & inspect. Talcum power on area can help show oil. But might be hard to keep power on in wind. Don't jump to conclusions, do the diagnosis so you know what the leak(s) are.

Also oil from prior repairs, know as residual oil can take days to wick out of the nooks & crannies of motor.

Retorque of head sometimes helps seeping gasket. Always recheck valve adj after head torque.
Don
 

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Hi Andy,

steady 30 miles or so. Got back
'talcum powder'
test
start engine and observe the suspect area for a period;
If it doesn't leak visibly at a standstill, go for a ride
stop frequently to see the first signs of the leak.
Mmmm ... how long did you have the engine on tickover watching for possible leaks before you set off and how many times in that "30 miles or so" did you stop and check possible leak sites?

Imho, your assumptions are only reasonable if you first saw the oil on the drive-side outer exhaust rocker box stud and on the fins just either side of the top of the exhaust PRT but nowhere else. Otoh, if you didn't watch the potential leak sites for several minutes before riding and then rode forty, sixty minutes without stopping, aerodynamics of unfaired air-cooled motorcycles are weird, the oil could've come from lots of places.

Hth.

Regards,
 

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I would have to agree with Stuart on this one. It's probably just a leaky gasket. Try tightening down the bolts first though.
 

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Discussion Starter #12
Hi,

Yes, I think that a head re-tighten is first thing to try. Checked my log book and found I re-torqued head annd re-set valve clearances around 750 miles ago. I used a composite head gasket. Will report back after i have done this.

Andy
 

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Discussion Starter #13
Hi,

Small update: I re-torqued the cylinder head this afternoon. All the bolts took part of a turn to click the torque wrench, then re-set the valve clearances. Will probably not get to ride bike until Saturday.

Andy
 

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retrorod

This leak is pretty common and can be problematical to fix. IMHO its always about a new gasket. Thin paper gaskets will do if Permatex Aviation sealant No3 is used both sides. There are other gasket types (compressable) that have varying material in them, but they come at a price. The machined surfaces are usually pretty shi*ty (even from the factory) so anything you do to ensure real flatness will pay dividends over time. HTH. RR
 
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