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Rusty's Bad Habit

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jcatnite

jcatnite

Jedi Knight
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Hello all,
Rusty, my 76 midget has developed the bad habit of smoking as of late. It doesn't do it all the time but it seems to be getting more and more regular. It's oil smoke to be certain but I'm not seeing any really bad fouling on the plugs. The engine smokes pretty heavily when I first take off from a light and gets better with each gear. By the time I'm into 4th there is no smoke that can be seen by someone following me. But after I slow down at the next light the cycle starts again. I'm thinking it could be one of two things. Badly worn valve guides or the emission system sucking oil from the valve cover through the carb. Any ideas from the experts?
Thanks in advance,
JC
 
I run an open valve cover breather into a catch tank, with the splash shield inside the valve cover removed, and I only get a slight film in the clear plastic tube to the catch tank. I doubt that you're getting oil in the intake, given my experiences (while autocrossing, no less). I can't speak to the valve guides, however. Hope this points you in the right direction!
 
Do a compression test with a cold engine and record the values.
Then warm up the engine and do another compression test.
If the values are a lot different (more than 20%) you are likely to have bad rings. If they are not much different, it's likely valve guides (or a problem with the crankcase breather system...but this is not likely unless you've modified it).
A "leak-down" tester is even better to discern whether it's rings or valve guides, but these are not commonly available.
Sometimes a stuck carb enricher (choke) can create an oil smoking problem.
 
Sage advice Nial. I plan to give it a once over this weekend. I know the rings are worn as other compression tests have revealed but the smoking is a new thing. It seemed to start when I started monkeying with the emissions piping but it could be coincidental since I let it get a little low on oil at about the same time.
JC
 
Cool man, we get up that way every now and then. Small world isn't it?
JC
 
I'm bumping this post back up to the top to update everyone on my continuing saga and to verify my suspicions. Rusty, my 76 Midget, through a curve ball at me. When I bought the car, the hot compression readings were pretty much 125# across the board. I could put a few ml's of oil in each cylinder and it would bump up to 165 or so. I thought then, engine is worn and will need new rings soon. Last night I took hot readings and this morning I took cold readings. I was a little blown away by what I found.
Hot Cold
#1 165 170
#2 167 170
#3 162 170
#4 162 167

Here is what I have done to the engine between the tests. New thrust bearings, rod bearings, main bearings, timing chain, timing tensioner, and oil pump. The timing chain was extremely loose and the tensioner was laying in the bottom of the pan. I'm thinking it could have been affecting my valve timing enough to lower the initial readings? There are two possible conclusions in my mind. The valve guides are so worn that it is letting oil be sucked into the cylinders when the engine is under deceleration or the oil rings are so worn that there is so much oil on the cylinder walls that the compression rings are sealing better than before..lol. I'm pulling the head today, as I have a burnt exhaust valve on #2 and I just have to know what is going on below it... Anyway, sorry for the long post, any advice is welcome. I would love to hear what others think about the increase in compression readings.
JC
 
Hi JC,
I can think of two possibilities, maybe a combination of the two.
First, a comment. The "burnt exhaust valve on #2" is not showing up as leakage on your compression readings.You may have had tight valve lash on #2 which was corrected during the other work.

There may have been some valve or ring seating issues that were improved with further running. ie: Tight valve lash, if corrected soon enough, will let the valve re-seat itself to some extent.

A loose timing chain will retard the overall cam timing. This causes the intake valve to close later on the compression stroke & would cause lower cranking compression pressures. Compression can't start building until the intake valve gets fully closed.

Note, 2 cc's of oil in the combustion space might raise the pressures around 5% due to it causing a slightly higher compression ratio. Your improvement was more like 30%.

While loose valve guides could cause excessive oil consumption, valve stem seals could be replaced or added without pulling the head.

Are you sure that you want to pull the head? Things look awfully good to me. With compression readings that high & uniform, I would just run it for a while & see what develops.
D
 
As an aside (concerning your questions about worn valve guides). After finding that my 3 cylinder 1500 engine was running on only 3 cylinders due to a blown head gasket, I took the head down to my engine guy. He checked the head for flatness and we found it was out by .004". However, he mentioned that we'd never put proper oil seals in, which (even though the valve guides are virtually new, 3000 miles, etc), the car smokes a bit on start-up and the plugs are generally slightly black. So, we looked through some catalogs and found that there are valve seals available for a 5/16" valve stem and .502 valve guides (what we've got on on my head, at least, and probably everyone else's). This means that seals can be retro-fitted if one looks at dimensions instead of looking by application. So, it may be that the valve guides are not in as bad a shape as you think, and are actually moderately salvageable. The oil problems could be contributed to by the lack of a proper seal.
 
Thanks guys. You are probably right. Things are pretty tight in the engine it just smokes like a freight train everytime I take off from idle or from a deceleration point. I'm rethinking pulling the head. I will measure my valves and guides and see if I can't come up with some to add. It might improve things a little.
Oh and Dave, the only way I know I have a burnt exhaust valve is that i found it during a leakdown test. I could hear the air moving through the exhaust and barely feel it on my face at the end of the pipe. As far as ring leakage, I could feel a noticeable breeze at the valve cover breather tube. I'm not sure how much is too much there. My rig is home made and the supply piping is bigger than the port in my plug adapter...i.e. the gage always stays around 98psi.
Thanks for the advice guys, I think I will follow it as always, I think I remember reading somewhere that vavle seals from a ford pinto (I hate to go there)engine will fit. I will let you know which application I end up with.
JC
 
[ QUOTE ]

Oh and Dave, the only way I know I have a burnt exhaust valve is that i found it during a leakdown test. I could hear the air moving through the exhaust and barely feel it on my face at the end of the pipe. As far as ring leakage, I could feel a noticeable breeze at the valve cover breather tube. I'm not sure how much is too much there. My rig is home made and the supply piping is bigger than the port in my plug adapter...i.e. the gage always stays around 98psi.
JC

[/ QUOTE ]
Hi JC,
I'm not sure that you present leak tester will tell you much. You need a pressure regulated air supply, a gage, & most important a .040" restrictor. Possibly .030" on smaller engines & .050 on larger engines. With an endless supply of air, no restrictor, there is no way to tell how much actual leakage there is. Small pressure regulators & quick disconnect couplers are fairly cheap & will give you meaningful readings.

I have attached a sketch of a simple but quite accurate tester that you can make. The restrictor can be one of the fittings that is soldered closed & a .040" hole drilled through the solder.
D
Edited - a couple of examples:
A good well built race engine will have 3% leakage or less.
A good street engine will have about 5 to 8 % depending on amount of wear.
An engine can still run pretty well with 12 % leakage, but power will be noticeably down, & starting will be harder.
D
 

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i can think of about 3073 posts that could go there.....



mark
 
That sketch definitely does belong there. I was going to ask but looks like Basil beat me to it. Oh and Mark, its 3074 now...lol but I didn't miss the reference...
JC
 
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