Engine Health Check/Inspection. AJP8 Technical Info please!
Discussion
As my body-off refurb is coming along, slowly, I'm pondering what to do with the engine whilst it's out. It's a '96 engine and has done 83000 miles without, as far as I can tell, any work done bar standard servicing. I certainly don't have any paperwork with the car to evidence any engine work. If the valve shims continue to wear at their current rate I might be looking at a top end rebuild by 100k miles, equally the rate of wear might slow down & extend the engine's life, who knows. The chassis is off being blasted and painted at the moment & I've replaced all the heatshield on the car. Once I've got the chassis back on the car and the garage tidied up a bit I expect to have some space and time to have a look at the engine.
I'm sure other options are available, including 'just leave it alone', up to 'deep pockets rebuild to 4.7'. I don't have the cash for an engine rebuild on a whim, so that option is out but I'd like to do what I can to learn/further my spannering abilities in general and learn something about the state of my engine in particular.
Whilst I've not opened an engine up before I'm hoping that a bit of advice from some more experienced spanner turners on PH will enable me to further my knowledge; specifically, what I need to check, in some cases I'm sure, how to do it. I'm equipped with a torque wrench, digital calipers, a micrometer and a decent socket set. I've also rebuilt the T5 gearbox, and, with some helpful suggestions from PH, got the body off, so I'd like to think I'm not a complete novice anymore.
I'm thinking I might as well do the valve clearances again, and change the cam chain. Whilst the front cover is off I'm tempted to get the sump off for a look & clean up if there is any gunk that can be removed. That also opens up the option of checking big end and main bearing clearances. Should I do this with plastigauge? I know the engine build manual specifies tolerances at build but does anyone have some service limits for clearances, crank journal dimensions (diameter, ovality, taper, anything else).
What else can I check? I suppose I could check piston-bore clearance and/or ring gap but that would have to be at BDC so I'm not sure how useful it'd be. Thoughts? Info? Whats an acceptable tolerance for an engine that's in use, and whats considered 'past it'?
Valve guide wear seems to be another issues found when engines are stripped for rebuild. Any way I could get some assessment of that without taking the heads off? Also, what's acceptable and whats not?
I also do have an engine leakdown tester, but it's a cheap ebay effort so whilst I could have a go I'm not sure how much faith I should have in any results it gives me.
I'm sure other options are available, including 'just leave it alone', up to 'deep pockets rebuild to 4.7'. I don't have the cash for an engine rebuild on a whim, so that option is out but I'd like to do what I can to learn/further my spannering abilities in general and learn something about the state of my engine in particular.
Whilst I've not opened an engine up before I'm hoping that a bit of advice from some more experienced spanner turners on PH will enable me to further my knowledge; specifically, what I need to check, in some cases I'm sure, how to do it. I'm equipped with a torque wrench, digital calipers, a micrometer and a decent socket set. I've also rebuilt the T5 gearbox, and, with some helpful suggestions from PH, got the body off, so I'd like to think I'm not a complete novice anymore.
I'm thinking I might as well do the valve clearances again, and change the cam chain. Whilst the front cover is off I'm tempted to get the sump off for a look & clean up if there is any gunk that can be removed. That also opens up the option of checking big end and main bearing clearances. Should I do this with plastigauge? I know the engine build manual specifies tolerances at build but does anyone have some service limits for clearances, crank journal dimensions (diameter, ovality, taper, anything else).
What else can I check? I suppose I could check piston-bore clearance and/or ring gap but that would have to be at BDC so I'm not sure how useful it'd be. Thoughts? Info? Whats an acceptable tolerance for an engine that's in use, and whats considered 'past it'?
Valve guide wear seems to be another issues found when engines are stripped for rebuild. Any way I could get some assessment of that without taking the heads off? Also, what's acceptable and whats not?
I also do have an engine leakdown tester, but it's a cheap ebay effort so whilst I could have a go I'm not sure how much faith I should have in any results it gives me.
Fair enough. One thing I have wondered about is whether it has had any engine work done. I have some receipts with the car but a lot of it's early life is a mystery. The dipstick is in the wrong place for a '96 car so whilst it's likely that it's simply been replaced at some point with the later style I do wonder if this car snapped it's crank early on and had a rebuild. Some of that might be hope too as it'll make any subsequent rebuild significantly cheaper (or at least one less decision to make) if it turns out I have a good large journal crank.
If and when the time comes I'll remove and refit the engine myself. In an ideal world I'd have a 'countdown to rebuild' timer that hits 0 just before something goes catastrophically wrong, resulting in ruined heads, or block, shattered crank, etc etc.That would allow me time to have a rebuild fund sorted as well as having got maximum value out of the original engine. If I'm best off leaving it alone, but if there's some things I can do while the engine is out to assess how worn it is and how long it might have left, then great.
Useful info. Thanks all. I'll replace the timing chain & see what the state of the tensioner is. Might take the opportunity to mark TDC for each bank on the crank pulley too. I can do a leakdown test and see what that shows up. I'll consider taking the sump off but I think that'd mainly be for interest more than anything else.
However, does anyone have/know of of a manual which describes the wear limits for engine components, max ring gap, piston-bore clearance, crank dimensions, crank bearing clearances etc? Even if I'm not going to check all that now it'd be useful to have for the future.
However, does anyone have/know of of a manual which describes the wear limits for engine components, max ring gap, piston-bore clearance, crank dimensions, crank bearing clearances etc? Even if I'm not going to check all that now it'd be useful to have for the future.
Thanks, I've already downloaded a copy of the engine build manual which specifies tolerances for new engines. I guess the wear limits for components are still only known by a few engine builders. I can understand why they wouldn't want to share such information but it'd be useful for assessing the state of an engine thats run for 10s of thousands of miles.
After some disappointing leakdown test results, mainly indicating intake valve sealing issues, the engine is slowly coming apart Corroded head studs are making it slow work but with some penetrating fluid they're slowly coming off.. While its in bits I might as well check/change the main & big end bearings & piston rings as well as obviously getting the heads sorted.
Does anyone have a drawing/measurements of the standard 4.2L pistons so I can work out whether the liners or pistons are worn in the event that I find piston to bore clearance is out of spec once the heads are off.
Does anyone have a drawing/measurements of the standard 4.2L pistons so I can work out whether the liners or pistons are worn in the event that I find piston to bore clearance is out of spec once the heads are off.
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