Kyp Posted August 4, 2016 Share Posted August 4, 2016 Hi all,I started working in earnest to get my Spit back on the road (after too many years standing). Having got it running I now have bad compression which I'm hoping is the reason it will struggle along for half a mile before giving up and not restarting without a rest...Anyway, I figured that the bad compression is caused either by leaky valves or piston rings. So the head is off (gasket looks ok) and valves will be reseated, but is there a way to check the piston rings with the head off. I've heard of pouring oil in to the cylinders and recording the amount of time it takes to drain past the rings?I'm suspicious of the rings as plugs 1 and 4 are black and as if the mixture is rich (fed by different carbs) and appear to have oil on the threads, the top of those pistons is also particularly cruddy. I haven't been loosing oil but then haven't driven very far!I could just replace the rings of course but figure it's better not to disturb them if they're ok.Any advice would be appreciated! Quote Link to comment Share on other sites More sharing options...
Velocita Rosso Posted August 4, 2016 Share Posted August 4, 2016 Did you do a compression test, and the ratings? Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted August 4, 2016 Share Posted August 4, 2016 If the engine was ok before standing for years then either the rings are stuck or the bores have been damaged by rust. The latter should be fairly obvious, the former - not. Do all the bores look good without rust marks, vertical scoring or discolouring? Is there much of a wear lip at the top?If you know the engine was ok before then it may be worth putting some ATF in the bores and leaving it to stand for some time (days to weeks preferably) as ATF is good for unsticking things like that. There are no guarantees though. If you don't know what the engine was like before then it is probably worth pulling it out and looking at it properly.Nick Quote Link to comment Share on other sites More sharing options...
Kyp Posted August 5, 2016 Author Share Posted August 5, 2016 When I first got it running again several months to a year ago it was running very unevenly (as you might expect) so I did a test and compression looked ok - was getting 147-160 across the four. I since decided I wasn't finding enough time to get everything done and took it to a garage to push thing forwards. Three garages, a trip around the Oxfordshire countryside and no small amount of teeth sucking later, the car was home again, nobody wanted to take it on. But the last garage did another test and got low readings, to be honest I can't remember want these were, low hundreds I think.Anyway, I'm kind of glad it has motivated me just to plough on myself. So, I haven't started cleaning anything up yet but the cylinders look clean, with the exception of number 4 which has some very faint vertical scoring, fairly evenly spaced lines every 3mm, which you can't feel but can't rub off either. As for a wear lip at the top, I need to investigate there is certainly a build-up non all four between the end of travel and actual rim of the cylinder...ATF? Excuse the ignorance... transmission fluid? Quote Link to comment Share on other sites More sharing options...
Kyp Posted August 5, 2016 Author Share Posted August 5, 2016 Picture of scoring attached... Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted August 5, 2016 Share Posted August 5, 2016 ATF = automatic transmission fluid. The basic dexron II.You'll need to scrape the carbon layer off before you can assess the wear ridge. Will usually be more pronounced on the thrust side (manifold side).Odd marks on the bores. Possibly indicative of broken rings. #4 is the most prone to hot running due to being furthest from the pump and water jacket sludging.Nick Quote Link to comment Share on other sites More sharing options...
Kyp Posted August 5, 2016 Author Share Posted August 5, 2016 Thanks Nick, will see what I uncover when I start cleaning it all up tomorrow.Trevor Quote Link to comment Share on other sites More sharing options...
Kyp Posted August 8, 2016 Author Share Posted August 8, 2016 Cleaned up my valves and top of the block this weekend and all seemed to be in order until I noticed the extra amount of moment in piston 4... they can all be rocked very slightly but number 4 just has that little bit more movement.I guess this means worn or damaged rings? All pistons are currently soaking in ATF and I'm hoping this will improve the compression so that I can address the piston at later date as budget is limited and the main objective is to get it back on the road before working through all the issues. Before coming off the road, when compression was ok, the engine had a tapping that sounded just like a loose tappet but I was able to solve through adjustment. I'm now wondering whether this was a bit of piston slap. On the plus side this would mean the piston already had some movement and isn't related to the low compression which was caused by the some seizing during the period of standing.Anybody have any thoughts? I imagine popular advice would be to just inspect and change the rings! Can this be done without honing the cylinders? Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted August 8, 2016 Share Posted August 8, 2016 New rings should not be fitted without honing the cylinders, though this can be done (after a fashion) in situ with a tool in an electric drill.Up to you whether to take this step. Trying it as it is will cost you a head gasket set and some time. I wouldn't run it on too long if the problems with #4 remain though as the marks on the bore look a bit like they have a story to tell.I've seen a ~4 piston from a 1500 with truly devastated rings and ring lands where the engine was still running, even sometimes on 4 cylinders, with the main complaint being an inability to keep oil in the engine - what it didn't burn it puked out of any and every joint and seal due to crankcase pressure. Bore survived well though in this case. Quote Link to comment Share on other sites More sharing options...
glang Posted August 8, 2016 Share Posted August 8, 2016 Personally I think youre adding 2 n 2 to get 5 and talking up the problems. Its easily done as your mind finds clues to fit the conclusion youve already reached!How about finishing the valves, then putting it back together (which will only cost a few gaskets and time) and doing a proper compression check. Although your engine wont be like new I suspect its good for a few more miles yet..... Quote Link to comment Share on other sites More sharing options...
JohnD Posted August 9, 2016 Share Posted August 9, 2016 The purpose of compression testing is to compare the pressures across the block. Actual pressure is meaningless, as different gauges are not calibrated, which accounts for the different pressures you were told but as they were all even across the block indicate that rings were NOT the problem.John, from Rio Quote Link to comment Share on other sites More sharing options...
JohnD Posted August 9, 2016 Share Posted August 9, 2016 The purpose of compression testing is to compare the pressures across the block. Actual pressure is meaningless, as different gauges are not calibrated, which accounts for the different pressures you were told but as they were all even across the block indicate that rings were NOT the problem.John, from Rio Quote Link to comment Share on other sites More sharing options...
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