| Author | Message | ||
     Randy Roberson Frequent User Username: wascator Post Number: 859 Registered: 05-2009 |
When you test cylinder compression, do you open the throttle wide open or leave it closed? Seems to me it would make a diffetence in the pressure developed; also it depends on the specified compression and how it was taken I suppose. | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 331 Registered: 07-2018 |
Open... If you want the air to be compressed and show a true reading, you must let the atmosphere in. Some even remove all the plugs so the engine can spin as fast as possible. | ||
| Senart Patrice New User Username: senart_p Post Number: 3 Registered: 11-2020 |
hello, if I can help you with this ... Basic rules for taking the compressions of an engine. -------------------------------------------------- Check the valve clearance according to the factory settings (cold engine), Bring the engine to temperature (80 degrees Celsius, 185 Fahrenheit +/-) Remove all spark plugs Battery status (full charge or add a second battery) Take all the compressions of each cylinder with the accelerator fully open At this time you will see the real values Good luck Regards /P I hope that my English is clear | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 332 Registered: 07-2018 |
If you're going to start adjusting your valve clearances, take before and after readings. This of course assumes that your car is old enough where it doesn't have hydraulic lifters. | ||
| Senart Patrice New User Username: senart_p Post Number: 4 Registered: 11-2020 |
Hello Jeff, you are right, that's why I said ground rules !!! and forgot to specify that it was for engines without hydraulic valve lifters Regards /P | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 334 Registered: 07-2018 |
Randy has his car listed in his profile, I just remembered to check, it's 1970 Shadow. Doesn't have to worry about adjusting the valve clearance, but getting at all the plugs is a bear, or so I have read. I think some have removed the wheels and inner fender wells for easier access ??? This assumes he's working on his Shadow. | ||
| Randy Roberson Frequent User Username: wascator Post Number: 860 Registered: 05-2009 |
Thanks, all; I’m not testing compression in one of the Rolls-Royces; just inquiring in general. I rarely have seen this mentioned in specifications, and often see it being done on television with the throttle appearing to be closed; i.e. no one there to operate it and the tester is using a remote starter button. My opinion is it ought to be wide-open and plugs out, understanding we are looking for the outlier usually; the one that doesn’t measure up. . | ||
| Trevor Hodgekinson Frequent User Username: wm20 Post Number: 280 Registered: 11-2006 |
In reality it makes little difference to anything other than the time it takes to reach maximum pressure Throttle wide open will be 2 or 3 full cycles Throttle in idle position 20 or so . The caveat on this is your poor old starter motor is doing all of the work & getting very hot & bothered because very few are designed to run for more than a minute tops The other thing is you need to do the tests both dry then wet and at least 3 readings ( read all cylinders in a run then repeat 2 more times because it is easy to get a bad reading because the gear is not fitted properly . | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2528 Registered: 09-2004 |
Cylinder leakage test much kinder and tests so much more. | ||
| Trevor Hodgekinson Frequent User Username: wm20 Post Number: 281 Registered: 11-2006 |
Quite right Patrick The only time I do compression tests is on 2 strokes that I can not get to start. This is because it is a lot easier than blanking off the inlet & exhaust to do a leak down test & I don't charge if the job is not financially viable and very few hand held power tools are economic to rebuild . |
