ET: Engine (Twin) Am I Breathing Ok?

[nigsey]

Can anyone tell me what signs to look for if my crankcase breather is not working or how I can check if it is working correctly please? I have the standard breather pipe exiting down under the engine. The reason for asking is that I no longer seem to hear the exhalation of gases when I turn the engine over and there’s not as much emulsified oil coming out of the pipe as there once was. Also, I have noticed some slight oil leaks coming from around the oil pump cap, crankcase joint and banjos. Thank you, Nigel.

 

[oexing]

Possibly the alu breather sleeve has seized a bit on its spindle and shifted in the gear. So now the timing is wrong and the engine pressurizes from this. When you blow into the breather pipe at the front of engine there should be connection to inside once the piston passes TDC on its way down and breathing should stop once the piston has passed BDC. At least that is my idea . . . ?

Vic

 

[nigsey]

That sounds perfectly logical, I guess I’ll have to find a clean piece of pipe and give it a go. Thanks for your suggestion. Nigel

Possibly the alu breather sleeve has seized a bit on its spindle and shifted in the gear. So now the timing is wrong and the engine pressurizes from this. When you blow into the breather pipe at the front of engine there should be connection to inside once the piston passes TDC on its way down and breathing should stop once the piston has passed BDC. At least that is my idea . . . ?

Vic

h

 

[davidd]

Testing the breather is a bit premature. Do a leak-down test and see how much compression is getting by the rings primarily. The valve seats and guides may be contributing to the leakage also. It is rare that a breather stops working and more likely that it is being overwhelmed by more compression leaking by the rings.

David

 

[Albervin]

Is this a newly built engine? Did you enlarge the slot on the breather? For new engines I fit an Elephant's trunk for a few thousand miles. When all the emulsified oil stops I fit the standard breather.

 

[nigsey]

Is this a newly built engine? Did you enlarge the slot on the breather? For new engines I fit an Elephant's trunk for a few thousand miles. When all the emulsified oil stops I fit the standard breather.

No it’s not a new build, there was around 11k miles on the clock after a rebuild in 2009, I’ve owned it for 2 years and I’ve done around 3k miles. It’s been running really well. I have very little experience with Vincent’s but I try and read up as much as I can about them. Thanks for your reply. Nigel

 

[nigsey]

Testing the breather is a bit premature. Do a leak-down test and see how much compression is getting by the rings primarily. The valve seats and guides may be contributing to the leakage also. It is rare that a breather stops working and more likely that it is being overwhelmed by more compression leaking by the rings.

David

Thanks David, I’ll do as you suggest, need to buy a compression tester, never done that on an engine before but willing to learn. Nigel

 

[Normski]

Thanks David, I’ll do as you suggest, need to buy a compression tester, never done that on an engine before but willing to learn. Nigel

David is referring to a leak down tester not a compression tester, he encouraged me to use one - they are far better than a compression tester.

 

[timetraveller]

Alternatively just get someone to stand on the kick starter with all the valves closed and walk aroung the engine and listen. You will easlily hear any leaks from the inlet valves via the carbs, any exhaust leaks are harder to hear but possible and if there are leaks past the pistons it will be obvious and your helper will not be able to stand on the kickstarter for long before is sinks down.

 

[bmetcalf]

I use the hose adapter from my compression tester to check for leak sites. With it screwed in the spark plug hole and connected to the compressed air hose, with the regulator turned very low, I can listen for any hissing at the muffler exit, each carb, and at one open valve adjuster cap.