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Very bad blow by - Help!

Ducdude

Well Known and Active Forum Website User
VOC Member
Was bad blow by - Now Head gasket

Gents it look like I have a crankcase pressure issue As I have blown out a push rod seal and oiled the entire rear of with oil leaking out of the push rod tubes, dynamo, and compression release seals. It is either a breather issue (which tested ok with the blow suck method)
Or I just have to much blow by for the breather to handle...

What are the ways to check for blow by...?
I have tested compression and it is 150 psi or so each side.

What are the other ways to check for how bad the blow by is?

If I use a D breather cap where on the bike should it go?
Why is it recommend to block off the stock breather when doing so..I would
think the more passage ways to get the pressure equalized the better?

Thanks,
Eric
Starting to think liners and rings over here (I really do not want to have
to do that now that the riding season is started...)
I also hate de-oiling my entire bike every 70 miles
 
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timetraveller

Well Known and Active Forum Website User
VOC Member
Eric, if you are getting 150 psi on both cylinders with a compression tester then it is probably not rings or a cracked piston and the valves and seats must be OK. A 'D' breather should go on the front exhaust valve cap, not the tappet cover, but it needs to have modifications to the upper valve guide and the head to let the gas pass easily. It might be a silly suggestion but are you sure that the timed breather is not open on the up stroke and closed on the down stroke? You could just check by blanking off the timed breather and temporarily fitting a 'D' breather to one of the tappet adjusting covers. It will throw oil out but should stop seals being forced out of their housings.
 

Ducdude

Well Known and Active Forum Website User
VOC Member
Eric, if you are getting 150 psi on both cylinders with a compression tester then it is probably not rings or a cracked piston and the valves and seats must be OK. A 'D' breather should go on the front exhaust valve cap, not the tappet cover, but it needs to have modifications to the upper valve guide and the head to let the gas pass easily. It might be a silly suggestion but are you sure that the timed breather is not open on the up stroke and closed on the down stroke? You could just check by blanking off the timed breather and temporarily fitting a 'D' breather to one of the tappet adjusting covers. It will throw oil out but should stop seals being forced out of their housings.

Am I sure that the timed breather is not open on the up stroke and closed on the down stroke? I would not bet my life on it as I did that test 5 months ago but I followed the instruction and was able to blow though the breather when I was supposed to and was not when it was closed according to KTB and a degree wheel...
When I built up the timing case I spent A LOT of time making sure the marks were properly lined up. I still may have mucked it up but I don’t think so at this point.

You said a 'D' breather should go on the front exhaust valve cap, (where the spring is at the very front of the motor correct?) and it needs to have modifications to the upper valve guide and the head to let the gas pass easily...
What type of modifications is needed on the head?? Is there any benefit at all if the breather cap is used with out making the modification?
Thanks all,
Eric
 

timetraveller

Well Known and Active Forum Website User
VOC Member
If you can get a look at a spare head with the upper valve guide in it you will see that there is a very small hole at the side of the valve guide to let the air through. On the 'D's the cut out in the head was increased to improve the area of the through hole and hence let more gas escape. Sadly a lot of people are unaware of this and just fit a 'D' breather and then do not understand why it does not work as it should. The gas has to get up the push rod tubes, past the rocker and the rocker bearing, up past the valve stem and then into the valve spring chamber. It can do that but it has an easier life if the final small hole into the valve spring area is increased. I do not have the exact dimensions but a quick look will show you where the hole has to be increased in size. As I said,for a quick test, you can just block off the timed breather and fit the 'D' breather to any tappet adjuster hole (either of the middle two would be best) and then just see if you have temporarily solved the problem. You will certainly loose oil through the new breather but not so much as to damage the engine with a quick ten mile ride. If it cures the pressure problem then you can think about what to do next. If not then we all have to think where the excess pressure can be being generated. Good luck.
 

deejay499

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VOC Member
I have two breathers on the Prince on the highest tappet covers.I like the idea that it breathes unobstructed by the rocker gear. I have just completed 800 miles running in and have only a little oil in the catcher pot.
 

davidd

Well Known and Active Forum Website User
VOC Member
Eric,

I cannot remember whether you were one of the people I sent the instructions to for timing the beather. If you were not I will send them to you. The compression test sounds good, but you are much better off doing a leak down test. If you do not have a leak down tester they are about $50. A leak down test will tell you exactly where the compression is going. I have nothing against changing breathers, but the timed one works well and I think you should check the engine with a leak down tester before you decide what to do.

David
 

Albervin

Well Known and Active Forum Website User
VOC Member
Eric, you could fit an elephant's trunk. Best to block off the timed breather. As a trial you could fit the trunk but let hit hang, fit a condom on the end and fire up the bike. The condom should blow up and then go down. If it takes off like a jet propelled franger then you have serious blow by and you may have to bite the bullet and take the head and barrels off.
 

timetraveller

Well Known and Active Forum Website User
VOC Member
Newsflash , Newsflash
Local vicar hit by flying object.
Late yesterday evening the Rev. Percy Poncealot was out taking his regular post prandial stroll round the local playing field where, as he states it, he likes to keep his eye on the local youth when he was suddenly struck in the ear by a strange object. The vicar stated that he first heard a strange rattling noise followed by a loud bang and then the sound of air whistling past a high speed projectile. He was suddenly, and violently, struck beneath his right ear by a hot but unidentifiable object. The vicar fell to the ground, where he was soon found, making lots of noise, claiming that his laundry bill was going to be seriously affected and that he had been assaulted by some form of possibly extra-terrestrial squid. The local police and ambulance services were called and the vicar cleaned up.
The object, which has a flexible outer membrane, contained some form of black hydrocarbon and smelt vaguely of high temperature combustion. Because of the possible extra-terrestrial nature of the object experts from the local university have been called in and the object has been placed into a hermetically sealed radioactive proof container and taken to the testing laboratories. A spokesperson for the university has issued a news bulleting stating that it is a great honour to be asked to carry out tests on what is possibly the first extra-terrestrial life form to be found on Earth and further bulletins will be issued as the results of various tests become available.
This news service will keep the world up to date as the information becomes available.
 
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