zKars Posted October 12, 2017 Author Share #13 Posted October 12, 2017 The last remaining mystery to me is the really obvious air leakage into the sump during the leak down test. Just how is that air getting down there? So I see two clues. First the ring end gaps. I popped #1 top ring off and stuffed into the bore, and measured the end gap. 0.020 ish. Hmmm, FSM suggests .010 to .015 is normal, with .040 max,. So .020 sounds ok, maybe a bit wide. With no obvious damage anywhere, about the only thing I see that is not "right" is a really random location of the three end gaps around the pistons. Some have the top ring gaps right next to each other, some are spaced roughly 1/3 of the way around. I likely moved them some while handling, I don't know how much weight to put on this. The walls were all well-oiled, how else does air get past the pistons? Usually I do this test with the motor buttoned up so I never get to hear whatever air escapes past the rings normally in a healthy engine? The leakdown tester was always saying the amount was well into the green/great/good region. I don't think this means too much. The head gasket was great, no issues there. Oil was water-less, water was oil-less. Finally I did a quick bore inspection. Only saw one scratch in #1 that can feel with a finger nail. Everybody else is nice and clean with clear hone marks. Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532209 Share on other sites More sharing options...
zKars Posted October 12, 2017 Author Share #14 Posted October 12, 2017 So we have a block with 250,000 + km. stock 86 mm pistons, evidence of engine work at some point, rings that don't look the age of the block, poor erratic compression ( that BTW does improve a bit with oil added) only one clearly bad cylinder valve wise, a timing chain with no tensioner, that must have slipped or was put back together without it, that resulted in in-consistent piston smoochin'', The other clues I noticed: -oil pan gasket is not a stock gasket. -chain guides were very worn. Not down to the steel, but grooved and very thin. So fellow detectives? What say you? Not that it matters, she needs a full round of rebuild love. Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532210 Share on other sites More sharing options...
Reptoid Overlords Posted October 12, 2017 Share #15 Posted October 12, 2017 How did the cam look?,if they were running the valves too tight would it produce some of the results that you noted? Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532217 Share on other sites More sharing options...
zKars Posted October 12, 2017 Author Share #16 Posted October 12, 2017 Cam looks fine. I did check the lash, some were tight but all were positive. Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532218 Share on other sites More sharing options...
240260280 Posted October 12, 2017 Share #17 Posted October 12, 2017 (edited) I agree with your theory...tensioner came apart and they just ignored the spring when returning the tensioner to its home. Chain timing was off when they put the tensioner back or it skipped a link or two due to the missing spring and caused the valve/piston contact. The timing chain being off also contributed to the lower compression and the bent valves contributed to the variance in compression. Edited October 12, 2017 by 240260280 Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532222 Share on other sites More sharing options...
grannyknot Posted October 12, 2017 Share #18 Posted October 12, 2017 I really thought there would be more damage to the top of the pistons. The tensioner is definitely the key here, like you said the spring was misaligned or pinched, the driver over reved it, the spring popped allowing lots of slop, the intake smacked the piston, the driver may have heard or felt something and backed off but the damage was already done. Tough engines. 5 hours ago, zKars said: No this is not a piston return spring. Must have been a hell of a ride! Ping ping ping Ricochet Rabbit Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532229 Share on other sites More sharing options...
Zed Head Posted October 13, 2017 Share #19 Posted October 13, 2017 I've wondered if a loose chain alone is enough to allow the valves to hit the pistons. Doesn't seem like it should unless the camshaft can some how rotate faster than the crankshaft is pulling it, from inertia. The inertia of the mass would have to overcome the valve springs and friction. Maybe at high revs, on a downshift, or something similar. With no tensioner on the loose side there would be a lot of slack to over-rotate on, if it's possible, even if the sprocket timing was right on the tight side. 1 Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532245 Share on other sites More sharing options...
sweatybetty Posted October 14, 2017 Share #20 Posted October 14, 2017 did you measure the pistons and bores? maybe someone bored-honed the cylinders without replacing the pistons, which would result in blow-by past the pistons. just an idea Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532363 Share on other sites More sharing options...
siteunseen Posted October 14, 2017 Share #21 Posted October 14, 2017 5 hours ago, sweatybetty said: maybe someone bored-honed the cylinders without replacing the pistons That would be a problem! Link to comment https://www.classiczcars.com/topic/58708-another-engine-another-mystery-another-day-in-the-life/?page=2#findComment-532375 Share on other sites More sharing options...
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