Compression test on an engine stand
08-04-2018, 06:07 PM
#1
Rennlist Member
Thread Starter
Compression test on an engine stand
Anybody done this?
Kevin
Kevin
08-04-2018, 07:13 PM
#2
Rennlist Member
Thread Starter
Never mind - I already own a leak down tester. Doh!
Kevin
Kevin
08-05-2018, 04:49 AM
#3
Rennlist Member
Kevin,
You can do a compression test on an engine stand- we did this with my 90 S4 engine when planning to transplant into the GTS chassis. The only problem I could visualise was that because the engine was not warm the results are not truly representative rather they are comparative and all we really wanted was to know was whether the valve train had experienced any damage as a cam wheel was cracked during the crash that took my S4. We found no compression on No7 and at that point decided to pull the heads and refurb the top end - that was a good decision irrespective of the two bent inlet valves we had to resolve. My motor when warm typically gives values in the range 185 to 190 psig but when cold I seem to remember it showed about 160 psig on the good cylinders.
The leakdown test will [I suspect] be more of a problem on a cold engine given it will leak more so I wonder whether such would have any real world value.
You can do a compression test on an engine stand- we did this with my 90 S4 engine when planning to transplant into the GTS chassis. The only problem I could visualise was that because the engine was not warm the results are not truly representative rather they are comparative and all we really wanted was to know was whether the valve train had experienced any damage as a cam wheel was cracked during the crash that took my S4. We found no compression on No7 and at that point decided to pull the heads and refurb the top end - that was a good decision irrespective of the two bent inlet valves we had to resolve. My motor when warm typically gives values in the range 185 to 190 psig but when cold I seem to remember it showed about 160 psig on the good cylinders.
The leakdown test will [I suspect] be more of a problem on a cold engine given it will leak more so I wonder whether such would have any real world value.
08-05-2018, 09:07 AM
#4
Rennlist Member
Thread Starter
When doing the compression test was there a concern about spinning the engine with no oil?
08-05-2018, 10:13 AM
#5
Rennlist Member
As I recall the test was carried out with oil in the sump- they literally pulled the motor out of the wreck, mounted it on the stand and spun it up .
I would think that the residual oil on the walls of the bearings/cylinder walls should ensure no issue for the relatively few turns one makes of the engine that is not firing at all. Doubtless there will be some more authoritative opinions on that..If the engine was drained of oil and sat for some time perhaps a different matter.
I would think that the residual oil on the walls of the bearings/cylinder walls should ensure no issue for the relatively few turns one makes of the engine that is not firing at all. Doubtless there will be some more authoritative opinions on that..If the engine was drained of oil and sat for some time perhaps a different matter.
08-05-2018, 05:08 PM
#6
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In terms of doing a compression test, the lifters are going to not get oil and will collapse, affecting the results.
