308 Piston Removal

I have a 1977 GTB and have a possible issue with the rings on cylinders #3 and #4 (the rear bank) and would like to remove pistons while the engine is in the car. Has anybody done this before? I have already have the head removed. Before I drop the pan I want to make sure there will be access to the connecting rod nuts. I rebuilt the engine myself a few years ago and when I installed the pistons, con rods and tightened nut, the engine block was removed from the tranny. The tranny casting also the forms the crankcase sump so while it is attached I want to make sure there still access to the con rod nuts. The tranny part of the casting partially extends under the rear of the engine block leaving some space towards the front of the engine. (front/rear I mean orientation of the car) I think the con rod nuts for cyl #3 and #4 would be toward front and accessible from this space. Before I start removing the pan, I just wanted to see if anyone else has done it. I would like to avoid pulling the engine

Why do I want to remove just 2 pistons, you ask? I rebuilt the engine myself a few years ago and did new valves, valve guides and seal and JE pistons etc. I have a few hundred miles on the engine but cyl #3 and #4 have never been right. I get blue smoke out the exhaust after doing a vacuum pull and when I pull the plugs on #3 and #4 they have been wet with oil. I pulled the head and there were a lot of carbon deposits on the exhaust valves and exhaust passages on #3 and #4. I cleaned the head and valves and see not problem with the head - no sign of wear on valve stems and guides, they fit perfectly with no play and the stem seals seem fine. I took the head to a couple of machine shop friends who build competition engines and they also found the head to mechanically fine. But since there was build up on the exhaust track plus the fact that the piston crowns on #3 and #4 were very clear compared to other cylinders, it was clear there was oil washing going on (instead of rich carburation or poor ignition or other problems). Since oil is not coming from the head, it must be coming through the rings. I am am not a professional car person but am careful when I do my work but can't be certain that I didn't damage the oil control rings or installed the oil scraper ring upside down or sometime like when I installed them. I would like pull the pistons and check.

Sorry for the long post. Thanks in advance for any help.
Jim

 

Thanks for the reply. I did a compression check at it was strong across all cylinders include #3 and #4 - about 165 PSI. Leak down was good and consistent across the board also.

I did put 10.5 compression JE pistons in the engine. I rejetted since I have high compression pistons and also a competition Tubi exhaust and think I got jetting mostly correct. The same jets in all the carbs and about the same idle mixture turn-out. Six cylinders seem happy, but #3 and #4 are not. I did not tune with an O2 sensor. Still running original points ignition and NGK BP5ES plugs.

As I said: I am running everything the same across the cylinders and six of them look are happy with clean valves and plugs but #3 and #4 have exhaust valve deposits and oily plugs.

Jim

 

Thanks for all the great advice! I am not currently suspecting rich carburetion since jetting and idle mixture screw turn-out of the carb feeding #3 and #4 is similar to the other carbs. I double checked that the float was not cracked and the needle valve was working correctly. Also, I am getting oily spark plugs. I am not suspecting ignition system fault since the other cylinders on that distrib are fine.

I believe the second compression ring is a tapered ring to help scrap oil so putting it in upside down could allow oil passage. If I was careful about orientation when installing but not absolutely sure I didn't make a mistake.

The cylinder walls on all cylinders are nice a smooth with bit of the cross-hatching still there. All the pistons slid freely when I installed them.

Jim

 

Excuse my mis-terminology about the second compression ring.

I had the cylinder liners bored 40 mils over and the pistons were matched to the liners with the JE specified piston to cylinder wall clearance. Ring gaps set to specs.

I am going to call JE today for some tech advice.

Jim

 

Rifledriver,
Thanks for the advice and the article was very informative.

I called JE and the ringset I installed has a tapered style second ring. They said if I installed that ring upside down then the ring would be scraping oil up instead of down and would be causing the problems I am experiencing. I knew of ring orientation when I installed them and I am generally very careful when doing work, but I can be certain that is didn't make a mistake. I will look at it some more, but I am thinking I may end up removing the two pistons.

Curious that if a made a mistake on ring installation, I did it on just two adjoining pistons. But anything can happen.

Jim

 

Thanks for the replies. A couple of photos might be helpful. I already have the head on that bank removed. In picture below cyl #3 and #4 are the top two and their piston crowns are very clean compared to the other two. (The little drops of liquid on the pistons are a few drops of coolant remaining in the head when I removed it. I took this pic right after I pulled the head). I borescoped the other bank and the piston crowns had deposits similar to #1 and #2 in the photo below.

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Also, the exhaust valves and exhaust passages in the head of #3 and #4 have deposits on them compared to #1 and #2. As I said before, the spark plugs on #3 and #4 would get oily wet when the engine is running and the others remain dry. I checked the head and a couple of other people checked the head and the valves stems and guides show no wear and the valve temp seals are good. All this make me suspect the rings.

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I dropped the oil pan and answered the question if a piston could be removed with the engine in the car. No, It cannot. As pointed out be other posters: the windage tray cannot be removed which needs to be removed to access the con rods. The tray is held in by 4 nuts and the forward ones are accessible but the rear ones are blocked by the part of the tranny that comes under crankshaft. Even if I could get all the nuts out, the tray is too big to remove though the pan hole. So this would require an engine out, remove the bell housing and separate the engine block from the tranny/sump casting.

This is a lot of work and I got a lot of other projects I want to finish this winter. So, I am thinking I will put the oil pan and head back on and running it for another summer and just keep the spark plugs clean. Next winter I will budget the time and mental energy to do an engine out.

Thanks for all your help.

Jim

 

Thanks for all the replies! I will be looking into adding the MSD ignition units.

Jim