ET: Engine (Twin) Am I Breathing Ok?

[davidd]

A leak-down tester allows you to attach your compressor to the spark plug hole, which is comparable to standing on the KS. I usually remove the pushrods through the rockers to do the test, which will keep the valves closed. The object is to listen at the carb and exhaust pipe to note how much air is seeping by. The tester itself will measure the excess airflow and give you a percentage of how much extra air is slipping by.

It is the best thing to do short of a tear down to determine the condition of rings and seals. A once-a-year test would be a good way to tell when the top end needed a teardown. Racers often do them at the end of a race weekend.

https://www.amazon.com/CHEINAUTO-Cylinder-Compression-Diagnosis-Pressure/dp/B0913FJNXK/ref=asc_df_B0913FJNXK/?tag=hyprod-20&linkCode=df0&hvadid=533235061664&hvpos=&hvnetw=g&hvrand=7707376120052687371&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9011841&hvtargid=pla-1395043067033&th=1

I had a top ring crack and it immediately jumped to 60% blow-by. It is hard for the breather to keep up with such a high rate of blow-by. Normally, I would keep it down at .5% to 5% for racing. Street use can be more generous, but at least you will know what you are up against.

David

 

[ClassicBiker]

They are not that difficult to make. I made mine after looking up leak down tester plans. You just need a 0.040" to 0.060" diameter restriction between the two pressure gauges. Youtube has plenty of instructions on how to as well. It helped me identify that my front cylinder was my problem child when the lower exhaust valve guided made like Elvis and left the building. It also confirmed all was well after rebuilding both cylinder heads. I did both just to be on the safe side.

Build Your Own Leak-Down Tester

Converting a Harbor Freight compression tester for aircraft engine use.

www.kitplanes.com

Leak Down Tester - Build and Use Your Own | www.darkside.ca

www.darkside.ca

 

[Normski]

Car Vehicle Cylinder Leak-Down Tester Leakage Petrol Engine Compression Detector | eBay

Leakdown Detector Kit. Designed to check the amount of leakage in 4-stroke engines. Designed to detect a variety of common engine faults such as worn piston rings, cylinder head cracks, worn valves and blown head gaskets.

www.ebay.co.uk

This one on Uk eBay looks very similar to the one in davidd’s post.

 

[nigsey]

Many thanks everyone for your replies and advice. Leak down testers are inexpensive so that’s not a problem, unfortunately I don’t yet have the necessary air compressor and they’re not particularly cheap. It ‘a is been on my list of workshop must have’s though, so I guess I’ll have to make one a priority now, unless I opt for the free ‘stand on the kickstart method. Nigel