blunderus Posted June 20, 2018 Share Posted June 20, 2018 (edited) Hi all Just wanted to ask a couple of question of those with knowledge where mine ends. This is a long story but I will try and condense as much as poss. Right, I have a 370z 2011 with 68k miles on the clock. I have owned it since new so just over 7 years. It is totally stock and always serviced at main dealer. It has rod knock! Big end bearing is non existent. I have taken engine and gearbox out myself and stripped all the Gubbins off etc. I am going to compression test it on the bench before I strip the motor using battery and starter motor. I am doing compression test as there appears to be more issues i will get to shortly. First question. Will I see a difference on compression on the cylinder with rod knock and if so higher or lower? I was thinking high as the play would allow the piston to lift higher on the compression stroke? On to the other issues. Related possibly? This all started with one of my catalysts falling apart whilst driving home one evening, puff of blue smoke and lose of power. The Off side cat was in a multitude of bits. I replaced the cat, as Nissan wanted 1200 quid, assuming that would be job done. Once the horrendously loud Cat rattle was gone it became obvious there was more to it. Still no power and obvious rod knock noise. For a few months previous I was have a lot of engine flooding issues and low hunting idle. Car wouldn't have flooding for a couple of weeks then the next 4 or 5 starts it would be flooded even after long drives and I would have to plant the throttle to fire up! Lumpy idle was pretty constant. No engine warning lights and Nissan failed to find the issue. When removing engine the plugs on the off side appeared fouled with, I believe, fuel. Further info. Destroyed cat and fouled plug on off side bank. Cylinder with rod knock on near side but plugs nearside looked spot on! Thoughts ???!!!??? Edited June 20, 2018 by blunderus Quote Link to comment Share on other sites More sharing options...
StormWhite Posted June 21, 2018 Share Posted June 21, 2018 In answer to question 1 I would think lower as the compression stroke would force the piston lower resulting in lower compression reading. Quote Link to comment Share on other sites More sharing options...
blunderus Posted June 21, 2018 Author Share Posted June 21, 2018 I was thinking that without engine spark just before tdc to keep the rod pressed against the crank the upward momentum of the crank would throw the rod up closing the gap on the underside of the crank. That would allow the piston to lift higher increasing compression. I was assuming this is one of the reasons rod knock sounds worse with ht lead removed? Not sure though. That was just my theory. Quote Link to comment Share on other sites More sharing options...
coyoteboy Posted June 22, 2018 Share Posted June 22, 2018 (edited) Not when you're compressing a ton of air - piston/rod mass at cranking speed will not create enough force to overcome an 11:1 compression ratio air spring at TDC. Rod knock can occur with ~100 microns of (extra) bearing clearance - you won't have a compression tester capable of the resolution needed to see the change due to it and cycle to cycle variation due to ring sealing, valve sealing and other things will be higher than you see with the bearing play. Edited June 22, 2018 by coyoteboy Quote Link to comment Share on other sites More sharing options...
ZMANALEX Posted June 22, 2018 Share Posted June 22, 2018 Pointless discussion as the difference will be minuscule and as been said you won't have a compression tester capable to see the difference. Quote Link to comment Share on other sites More sharing options...
blunderus Posted June 22, 2018 Author Share Posted June 22, 2018 Okay gents. Thanks for the input. I will be testing some point tomorrow so will let you know the readings i get. Quote Link to comment Share on other sites More sharing options...
blunderus Posted June 23, 2018 Author Share Posted June 23, 2018 I believe I have identified the cause of my engine woes. I have removed my lower sump and in it I found what appears to be a piece of oil galley gasket! I believe this would have dropped oil pressure hence the rod bearing failure and I am pretty sure this would have been causing my lumpy idle also. Quote Link to comment Share on other sites More sharing options...
blunderus Posted June 23, 2018 Author Share Posted June 23, 2018 For those interested to know. 5 cylinders show 70-90 psi first beat and 205-210 psi on 8th beat. Cylinder with rod knock showing 60 psi first beat and 185 psi on 8th beat. Strip down starts from now. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.