Spare engine N42

[Dave WM]

This is the one I had the broken bolt on the exhaust manifold. Next up was a leak down test. Only #4 and #6 passed (about 80psi/75psi), on the rest it was more like 80/30 and you could feel the air coming out of the exhaust port. The valve lash was loose but I will check it again anyway, prob do a video. So now I will pull the head and learn about valve seats and valves. There are several machine shops in the Orlando area, I plan to call https://southeastcylinderhead.com/ Monday and see if they have experience on L28 heads. I did not bother to pull any of the crank shaft caps to inspect the bearings. will do that after I get the head worked out. I did not do a reg compression check since I don't have a way to spin the engine while its on the stand.

[Zed Head]

1 hour ago, Dave WM said:

I did not do a reg compression check since I don't have a way to spin the engine while its on the stand.

Could you use an air wrench on the damper nut?  Like the race engine starters.  Might spin you over instead of the engine.  Just a thought.

[Dave WM]

17 minutes ago, Zed Head said:

Could you use an air wrench on the damper nut?  Like the race engine starters.  Might spin you over instead of the engine.  Just a thought.

thought about it (the air wrench), even tried just spinning over by hand (on the damper nut) some psi readings of about 25 on a fast turn on the compression stroke. That's when I decided it just made more since to use the leak down tester, gives more info and does not require spinning.

[Dave WM]

I wonder if these are any good

https://www.ebay.com/itm/Exhaust-and-Intake-Valves-Fits-75-80-Nissan-280Z-2-8L-L6-SOHC-12v-L28E/253866960206?hash=item3b1ba6654e:g:rGsAAOSwa1ZcBvPQ:rk:44:pf:0

[Dave WM]

any different from these? (other than price).

https://www.ebay.com/itm/Datsun-280Z-1975-78-L28-L28E-Engine-Intake-Exhaust-Valve-Set-12-Valves-070-071/223310282539?epid=1434116639&hash=item33fe547f2b:g:qc8AAOxyRhBS8URB:rk:13:pf:0

 

[Dave WM]

I forgot to mention the plugs showed heavy carbon fouling and the exhaust ports had heavy carbon deposits lining them. I wonder if there could be some carbon build up around the exhaust valves make it hard for them to seat? The plugs were black with dry carbon.

I can't think of a way of telling that short of pulling the head.

[Zed Head]

Good reason to buy a bore scope.  They seem pretty inexpensive and of decent quality these days.  They probably have some that connect to your phone so you can snap pictures or video.

[Dave WM]

11 hours ago, Zed Head said:

Good reason to buy a bore scope.  They seem pretty inexpensive and of decent quality these days.  They probably have some that connect to your phone so you can snap pictures or video.

Got one of those, will look at it today. Only issue I have had in the past when into the plug hole is you can only see the top of piston. Maybe looking in thru the ports may show something.

 

[Dave WM]

I did some googling and found this article

Exhaust Valve Seat Leakage 971638

 

A 1.9L four cylinder engine was evaluated for leakage of cylinder charge through the exhaust valve seats. Fast FID HC analyzer traces reveal leakage. Static leakdown tests do not correlate with the Fast FID measurement, unlike previously published reports for a different engine. The causes of exhaust valve seat leakage are likely to be

• Flakes of cylinder deposits lodging in the valve seat
• Valve seat distortion due to the thermal and pressure loading of the cylinder head structure

Because deposit related effects are very history dependent, it is very difficult to obtain quantitative results.

Some experimental observations:

• Static pressure leakage measurements show variation of leakage area with cylinder pressure, caused by flexing of the valve head.
• Dynamic leakage results are history dependent. Leakage is reduced after running at high speed/load, and gradually build up during extended light load low speed operation.
• Valve closing forces can apparently affect leakage
• Particles of cylinder deposits are present in the exhaust port. These particles have composition similar to cylinder deposits but lower in carbon content and higher in oil ash. Particles were observed having 20-200 micron size. These deposits can lodge in the valve seat and contribute to leakage.

[Dave WM]

I know I have been accused of talking to myself, but this was just too interesting not to post about.

I started out with a 90/30 ish leakage about 67%. I tapped on the rocker (exhaust) and the low number jumped to about 50psi (more tapping did not have any gains). Next I tilted the engine and with the leakage happening I poured some fuel injector cleaner into the exhaust port, letting it boil from the leaking air. let it do that for a few min the tapped the rocker again, with a rag over the port so I don't spray cleaner all over. You can hear it pop of course but the more I did it the less of a hiss I got. I did this over several  cycles, until I got to the 78psi on the low number (about 13% leakage).

Next up I did the borescope, the piston top and the valve looked much cleaner from what I could see (not easy to see as bore scope has limited movement in the tight space). I compared my reading to the best cylinder (#6) which were pretty much the same low pressure of about 75-78.

I tried using power tools to spin the crank for a direct pressure reading, could not get it to work, but with a breaker bar I did hand turn it about as fast as I could thru one compression stroke and came up with about 75-78 psi on both #1 (treated cyl) and #6 (untreated).

I check the timing chain marks, they were correct (line centered in V) but I did notice the chain seemed to have a lot of slack, perhaps that is correct with no oil pressure, but I also noted the long guide seems very warn (had a deep groove where the chain runs).

At this point I am hesitant on what to do. the motor was purchased as a spare, and something to practice on. I am tempted to just bolt it back up as is to a transmission bell and install a starter to get a better read on the compression. then do the treatment to the remaining cylinders to see the effects.

 

 

 

 

 

 

 

 

 

Edited January 13, 2019 by Dave WM

[Patcon]

20 minutes ago, Dave WM said:

At this point I am hesitant on what to do. the motor was purchased as a spare, and something to practice on. I am tempted to just bolt it back up as is to a transmission bell and install a starter to get a better read on the compression. then do the treatment to the remaining cylinders to see the effects.

I don't see a down side to this. Do you?

[Dave WM]

Nope, was all geared up to do a complete disassemble, take head to a shop, etc... but I am in no hurry so the idea of a baseline run with minimal work seems logical.

My best cylinder reading now is around 90/83 lowest is 90/75. I am working on the lowest some  more this time with marvel mystry oil.