having rebuilt the engine some 16k miles ago, im some what suprised at the compression test result i just go today.
after 1200 mile after the rebuild, i tested is
cyl 1
184psi
cyl2
186psi
cyl3
185psi
cyl4
187psi
now today after 16k miles, and hard use with phase 2 etc.. i got this
cyl 1
161psi
cyl2
185psi
cyl3
180psi
cyl4
177psi
Why has cylinder 1 lost 23psi? im sure its a worn ring/bore issue, i did a we test and gained 10psi, it jumped to 170..
I was told last time prior to my rebulid that cyl1 closest to the water pump would wear quickly due to the bore being the coolest? what has this got to do with it?
I was told last time prior to my rebulid that cyl1 closest to the water pump would wear quickly due to the bore being the coolest? what has this got to do with it?
Dougal, have you bumped your head ? I understood that
It does sound like the rings have worn prematurely - I rebuilt my xe once and had a similar problem - new set of rings and a glazebreak, then it was fine.
I did have a couple of problems though which interrupted the run-in - not least of which was the oil cooler hose popping off and dumping all the oil, so pressure was lost for about 30secs.
the other thing is a faulty rebuild - perhaps the block was bored incorrectly or the rings gapped wrongly ?
well gary i did a test after 1200 miles and it all appeared fine, then also verified it at 6k miles its was more of less the same as my first test ...now today its not to bad on cyl 2 and 3 but 1 is 23 psi down and 4 is 10psi down
Would it be a worn bore? or worn rings?
im already at 86.5mm bore so i only have another step to 87mm before its time to junk it...
the end gap in the rings needs to be a certain size to allow for heat expansion - if it's too small the ring can't expand properly and will either crack or wear excessively.
I would've thought that would've shown up sooner though, if it was that.
badly lapped in valves lead to drop in compression testing. could be a valve need sreseting. however, i'm still used to the A series, it would appear this is far less on the XE/LET heads. Just for your interest though, I have just put an 86000 mile LET in davey boys mk3 astra, only mod is a slightly thicker headgasket and an XE inlet cam, it came out with this:
1. 165
2. 164
3. 165
4. 164
however, although its in the 160,s the thciker headgasket and XE inlet cam lead to that, AND that was cold, with forged pistons, results would have been higher if it was warm. however, my main point is that engine/head have done 86000 miles and never had new rings, or valves reseating so there is something to check. You SURE the valves we reseated properly?.
yup head was rebuilt, the bottom end was rebuilt..the valve seats were cut and i lapped the valves in...dave andrews did the head, i doubt it its the head at all or the wet test would not have given me a raise in pressure.
and as u say the wet test does suggest its a ring problem.
but, some thing has happend to cyl 1...very confusing....
You need a leak down tester, just screw it into the plug hole, with a compressed airline plugged into it, open the valve, and it compresses the cylinder, and you can here it leaking. listen in the exhaust, the intake pipe (intercooler one in your case,) and pull the disptick (most likely place it will come from, if your ring suspicion is right)
just to clarify - it relies on a known regulated supply (100psi nominal) leaking into the cylinder past a restrictor, and you then read off from a second gauge to get your % figure.
but primarily it's most useful as a leak location technique, as said.
if you have a compressed air supply, you could make a simple one by knocking out the core from an old spark plug, and rigging up a means to get the air into the cylinder.
but you also need to pay attention to the position of the cylinder in the bore - and making sure the rings are seated in the lands etc - it can get quite involved if you're tracking down a subtle ring problem.
I've got the test kit, but not the air I'm afraid - I spent ages building a tester, only to find that my little paint sprayer compressor was woefully indequate - I think it managed about 60psi
any decent garage will have leakdown facilities - but more importantly, people with the experience to diagnose it!
Gary, if you wnat to meet at my place, I have a suitable compressor to power your gauge if observer doesn't mind driving down here (its about an hour from london) I'm only 15 minutes from swindon.
Rich
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