breather

[oakesga]

My 1948 TC has an older engine which runs well but has some blowby which comes out the side of the engine. Unfortunately it also blows out some oil. Any suggestions on how to deal with this?

[Duncan M]

To help, we would need to know if you are running it all in stock configuration, or specifically what has been changed.

Having an aftermarket rocker cover, with no venting, can cause troubles. Using something other than the stock tappet cover and breather tube can cause troubles.

Dirty oil will make blow-by more unpleasant, and can also cause extra wear on the rings.

[Ray White]

Be sure the engine oil has not been over filled.

Check If the draught tube is clear. If this blocks it stops oily vapours from escaping.

Check that the rocker and side cover vents are also clear .

Excessive crankcase pressure from blow by indicates worn piston rings. A compression test would be helpful to establish the facts.

[Uwe Harlos]

Hello Ray,
how many bar or psi is the compression in a good XPAG Motor?
Thank you
Uwe

[Ray White]

Hello Uwe. I would not be too concerned about the exact compression reading. What is important is that they are all within 5 psi of each other. Much more than this then you need to establish why. Do the test with the throttle open and the plugs out. Make a note of the readings on all 4 cylinders.

A dry test with unequal readings can mean either blow by or poor valve seating.
To establish whether you have 1) a leaking valve or 2) blow by, you need to do a wet test. Squirt some engine oil into the bore; enough to cover the top of the piston.

Note the compression reading on all 4 cylinders. The oil will act as a seal against blow by and show up a leaky valve If you get unequal readings. More equal readings from a wet test indicate blow by.

[Duncan M]

A quick look at the WKF Wood period treatise on the XPAG will show the expected compression reading on a good "stock" XPAG with stock compression to be in the 90-100PSI range. page 7/54.

When the compression ratio is bumped up from stock 7.25:1 to 8.3:1 you can expect to find around 145psi. page 11/54

These long stroke engines perform remarkably well for their displacement, and can last a very long time--at low compression ratio's.

http://www.ttalk.info/WKF-Wood-XPAG-Engine-Book.pdf

[Steve Simmons]

Another way to determine if the rings or valves are leaking is with a leak down test. This will pinpoint where the leak is, and how bad it is.

As a "poor man's" leak down test, you can simply fill a cylinder with air pressure and listen for where the air comes out. If you hear it in the crankcase breathers, it's the rings. If you hear it in the exhaust, it's an exhaust valve. If you hear it from the carburetors / air filters, it's an intake valve.

[Ray White]

A quick look at the WKF Wood period treatise on the XPAG will show the expected compression reading on a good "stock" XPAG with stock compression to be in the 90-100PSI range. page 7/54.


http://www.ttalk.info/WKF-Wood-XPAG-Engine-Book.pdf

My apologies. I have removed the incorrect information. I should have checked first.!

[Uwe Harlos]

Vielen Dank allen!
Ich habe auf den 4 Zylindern eine Kompression von
1. Zylinder 11,5
2.Zylinder 11,5
3.Zylinder 12,0
4.Zylinder 11,5
Dann passt es ja super
Gruß
Uwe

[Ray White]

11.5 kgs force per square centimetre = 163.56 PSI
12.0 ...................................................................... = 170.68 PSI
(So perhaps I was right ?)

[Duncan M]

If those numbers are from an XPAG dry test, then the compression ratio of the engine is likely around 9:1 and about 75-80hp.

here is a different source for the WKF Wood XPAG document. Loads much faster from this source- http://www.tcmotoringguild.org/techinfo ... ewrite.pdf