What should the compression be on a 1981 SRX
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messina1974
- Posts: 30
- Joined: Fri Jan 08, 2010 1:49 pm
What should the compression be on a 1981 SRX
I was pondering changing pistons on my 1981 srx. I am having problems with starting it and have a set of new pistons and rings. Compression test revealed 120 and 110 pounds. What would a new motor have in regards to compression? Does it make sense to swap them out or not based on the compression tests. thanks guys MIKE
mmm that compression doesnt seem bad to me... how long is the hose on your gauge? the volume from the piston to the check valve in the guage will make different readings... the longer the lower the reading
My airbox is held on by one screw, not because Im lazy but because it is less weight!
Any questions or comments about this site itself can be directed to me at tylerochs@hotmail.com
Any questions or comments about this site itself can be directed to me at tylerochs@hotmail.com
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Bob Vehring
- Posts: 659
- Joined: Tue Feb 24, 2009 12:42 am
- Location: Milw. Wi
A compression test will give you a general idea on how things are sealing up, it is not an exact measurement, too many things can effect it. Is the engine warm or cold, do you have Arnold pulling the rope or is it PeeWee Herman? Is there a good film of oil on the walls to help the rings seal or has it all run down, are you holdng the carb open to allow air to flow or is it shut?
A better way to gauge the condition of the engine is to do a leak down test, but you need the tools to do it.
So the questions is, will new pistons help? Well I agree that 110 is on the low side of the usable scale, but why is it 110. Is it your gauge, your method of doing it or have your piston or rings worn?
A Chrome bore engine is designed so that the pistons wears, and the bore hopefully doesn't. The important measurement to a well running engine is the piston to wall tolerance, as this wears and opens up, you will loose compression. Cyl. walls can also wear and get out of round.
I understand that the tools needed, get over the limit of what most home engine builders own, but the answer is to mic. up the piston, then using a bore gauge on the cyl to determine its size and shape, that will tell you if you need pistons, or maybe just a new set of rings, or again, maybe its just your gauge or the way your doing the test
A better way to gauge the condition of the engine is to do a leak down test, but you need the tools to do it.
So the questions is, will new pistons help? Well I agree that 110 is on the low side of the usable scale, but why is it 110. Is it your gauge, your method of doing it or have your piston or rings worn?
A Chrome bore engine is designed so that the pistons wears, and the bore hopefully doesn't. The important measurement to a well running engine is the piston to wall tolerance, as this wears and opens up, you will loose compression. Cyl. walls can also wear and get out of round.
I understand that the tools needed, get over the limit of what most home engine builders own, but the answer is to mic. up the piston, then using a bore gauge on the cyl to determine its size and shape, that will tell you if you need pistons, or maybe just a new set of rings, or again, maybe its just your gauge or the way your doing the test