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Definition of 'blow-by'?

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Jim Lee

Jedi Trainee
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Hi Triumphants,

I've been away from my '59 TR3a for way too long and am trying to get back in its good graces. Just finished rebuilding the master and slave clutch cylinders after the hydraulics getting to the point that I couldn't get into first or reverse. If I can do it anyone can. Please feel free to ask questions as I have just done it. It really wasn't bad at all...and it actually fixed the problem the first time...which is a pretty amazing experience for me and
mechanical fixes.

In any case what I wanted to get was a defintion of 'blow-by'. What I am calling 'blow-by' is when I look at my
oil cap and see smoke coming out. The car is running really great and has since I have owned it but there has always been smoke ('blow-by'?) coming out of there. I have done some research on the web and have a vague idea about the primitive crankcase ventilation system on my trusty TR3.
My uneducated impression is that air is sucked in the from the strangely shaped pipe that is on the side of my engine on the drivers side...and it exits through the oil cap. I am assuming also that the reason I have this foul smelling smoke coming out of there is because my bottom end is in need of a rebuild. Most likely my rings are doing a poor job of sealing the compression chambers and oil is passing by them and then getting burned thus producing the 'smoke' that I see. Of course it is most obvious when I lift the hood after a run. When I am moving along it is not visible, though it is smellable, until I come to a stop. I have had the car for the last 4 years and haven't driven it nearly as often as I should but it at least gets a run around town every couple of weeks. What I am wondering is if I am correct in thinking that this is a problem with my rings and/or the shape of the inside of my cylinders and if it is
is there anything I could do about short of rebuilding the bottom end of the engine? I have heard that the 'mystery additives' found at all auto stores that promise to free up
your rings and stop all oil burning are largely wishful thinking.

The top end was rebuilt maybe a thousand miles ago so I am pretty confident about the integrity of that side of things.
I am going to start driving it more and keeping real close track of how much oil it is using but I know that it does use oil.

I suppose my main question is if there is anything at all I can do to postpone rebuilding the engine. It runs so nice and I have never done a rebuild before but I guess there is always a first time. There is probably not a whole lot anyone can tell me if I don't know how much oil I am burning
off but if someone could just explain in more detail than I have now what causes this smoke from coming out of the oil cap I would really appreciate it. I have always gotten incredibly good information from this forum.

Thanks very much,
Jim Lee
1959 TR3a TS50550L Black as the night
 
Hi Jim,
I would define blow by as anything that escapes past the rings into the crankcase. It could be unburned fuel mixture on the compression stroke or burned mixture on the power or exhaust strokes.

The road draft tube is intended to create a slight vacuum on the crankcase when the car is in forward motion. Air enters the top breather & exits the draft tube. When the car is not moving, there is no draft so the vapors exit from the top cap.

It is normal for a bit of vapor to exit the crankcase but not a lot. As you say, the rings are likely allowing some leakage. I have no idea how much is tolerable to you.

Newer cars have PCV valves which maintain a small amount of vacuum on the crankcase so that the vapor is drawn into the engine's intake instead of vented to the atmosphere. This is more effective than the road draft tube. You could add a PCV valve to your engine & help things a bit. It also reduces oil leakage some.
D
 
Thanks very much Dave.
"I would define blow by as anything that escapes past the rings into the crankcase."

The crankcase being that nasty void above the oil sloshing around in the oil pan and the bottom of the cylinders?

"It could be unburned fuel mixture on the compression stroke or burned mixture on the power or exhaust strokes."

So if part of what that smoke is vaporizing is fuel than I wouldn't necessarily be losing oil?

"The road draft tube is intended to create a slight vacuum on the crankcase when the car is in forward motion. Air enters the top breather & exits the draft tube. When the car is not moving, there is no draft so the vapors exit from the top cap."

So I had it backwards. The flow is from the top (oil cap/valve cover) then down out the draft tube. I forgot to replace the draft tube when I was doing the clutch hydraulics and I saw a bunch of oil splattered in new places
on the floor before I remembered to put that back in. Does that make sense? I was thinking that the oil could actually
splash out of that opening where the draft tube fits in. I haven't checked under there since I replaced it on my last ride. I was too excited about my getting the clutch to work .
It is normal for a bit of vapor to exit the crankcase but not a lot. As you say, the rings are likely allowing some leakage. I have no idea how much is tolerable to you.

"Newer cars have PCV valves which maintain a small amount of vacuum on the crankcase so that the vapor is drawn into the engine's intake instead of vented to the atmosphere. This is more effective than the road draft tube. You could add a PCV valve to your engine & help things a bit. It also reduces oil leakage some."

Is it possible to do that relatively unobtrusively. I am far from an obsessive about originality but is it 'simply' a matter of making and air tight connection from the current side draft tube to the underside of the manifold and putting a pcv valve in between? If the smoking is not that unusual and I am not burning alot of oil I am not really bothered by the asthetics of a little bit of smoke coming out at stop lights.

Thanks very much,
Jim Lee
 
Hi Jim I can tell you some of the stuff I have done. Yes I have trouble with that smell also. Anyways, depending on the condition of you main bearings and my buddy claims that they can last a long time and if the engine is not knocking (rod bearings). You can: (1) pop the head off (2) undo the rods (3) push the pistons up through the top (4) put some rings on (5) ball hone the cylinders and be done for about 100.00 bucks (gaskets and rings) I have done it with good results. A quality rebuild cost about 4 grand sooo. Anyway something to consider. This other guy I know actually puts in new rod bearings at this stage, but other research suggest that is asking for trouble because of the wear pattern already in place. Good luck, sorry but blow by is no easy fix.
George
 
"The crankcase being that nasty void above the oil sloshing around in the oil pan and the bottom of the cylinders?"

Yes

"So if part of what that smoke is vaporizing is fuel than I wouldn't necessarily be losing oil?"

Most of the "smoke" is burned fuel. Some oil vapor.

" I forgot to replace the draft tube when I was doing the clutch hydraulics and I saw a bunch of oil splattered in new places on the floor before I remembered to put that back in. Does that make sense? I was thinking that the oil could actually splash out of that opening where the draft tube fits in."

Yes. There may be some baffles or a deflector that prevents oil from directly exiting.

"Newer cars have PCV valves which maintain a small amount of vacuum on the crankcase so that the vapor is drawn into the engine's intake instead of vented to the atmosphere. This is more effective than the road draft tube. You could add a PCV valve to your engine & help things a bit. It also reduces oil leakage some."

"Is it possible to do that relatively unobtrusively. I am far from an obsessive about originality but is it 'simply' a matter of making and air tight connection from the current side draft tube to the underside of the manifold and putting a pcv valve in between? If the smoking is not that unusual and I am not burning alot of oil I am not really bothered by the asthetics of a little bit of smoke coming out at stop lights."

Yes. Get a PCV valve that is for a similar displacement engine, most auto parts stores, & connect it as you say. You may have to adjust the carbs a bit to compensate for the small additional manifold "air leak". The PCV is designed to have a small flow at high vacuum such as idle & more flow as the vacuum drops with the engine under loads.

You might even find a suitable valve & plumbing from a later model Triumph. I don't know just what year they may have changed the vent system. I'm not terribly familiar with the Triumphs so others may have some good suggestions.

As George says, if the problem is too severe, this won't completely fix the problem.
D
 
I'd go to Sears and spend 30 bucks on a compression tester and just see how bad your rings are so you know what you are dealing with. If the compression is even across the board, fairly normal, and you aren't burning oil out the tail pipe then you might be OK to just live with it for a while.
 
I could be wrong, but I don't think you can simply add a PCV valve without doing other modifications such as sealing off the hole in the block where the road draft tube is, and finding a correct valve cover with the correct oil filler cap, etc., etc.
 
Hi Andrew,
As Jim Lee said,
"Is it possible to do that relatively unobtrusively. I am far from an obsessive about originality but is it 'simply' a matter of making and air tight connection from the current side draft tube to the underside of the manifold and putting a pcv valve in between?"

He would be using the side draft tube sealed to a PCV as the vent exit, I assume his top cap is already vented as he said smoke was coming out from it. Air would flow in through the top cap, through the crankcase, & exit via the draft tube/PCV connection back to the intake manifold. A further refinement would be to run a hose from the vented top cap to the carb air filter. Caps with hose connections are available.
D
 
Jim
You now have excellent explanations on blow by.

IIRC, the liners in the TR3 are designed to be rotated 90° to account for some of the wear in the bore. That's an alternative if you are thinking or re-ringing the engine and dont'e want to bore. My old three had so much wear in the bores that the piston slap sounded like bells when you cold started it.
 
Billspit,

"the liners in the TR3 are designed to be rotated 90° to account for some of the wear in the bore. That's an alternative if you are thinking or re-ringing the engine and dont'e want to bore. My old three had so much wear in the bores that the piston slap sounded like bells when you cold started it."

Now that sounds like the bulldog engine I have been hearing about! I have taken off the head and shipped it off to a Triumph extraordinaire to rework so I know that I am at least capable of getting the head on and off BUT I almost had a heart attack when the guy asked me if I had turned the engine at all after removing the head and I had to admit that I had...just out of idle curiosity. Then he said well you have about a 50/50 chance of having ruined yer Figure Of 8 seal that sits at the bottom of liners....
Fortunately for once in my life I lucked out and there wasn't any damage done. He said it would real obvious in that there would be water all in my oil and the dipstick would look tragic.

So I am wondering...would I have to do much more than that to turn the bores and replace the rings? I am going to do a compression test as soon as I can to see where I am at but I have the distinct impression from all the reading I am doing here and other forums that I have at the least some sloppy rings. Is it possible to do them without removing the engine from the car and in the comfort and privacy of my own garage? I understand that there is some way of clamping the liners or something so to preserve the seal of the Fo8 gasket. Or if you are going to be going that far into the engine (to turn the liner 90 degrees for example) can you simply replace the hallowed Fo8 seal?

Also, I gotta know, when you were hearing those pistons slapping around like the chimes of freedom did you have smoke coming out of the oil cap making engine rebuilding signals?

Thanks very much,
Jim Lee
 
[ QUOTE ]
...I understand that there is some way of clamping the liners or something so to preserve the seal of the Fo8 gasket...

[/ QUOTE ]

Clamp the liners in place using some larger washers and long socket wrenches thusly:

head3.JPG


The cereal box cardboard over the pushrod passages are so I didn't drop anything in there.

Yes, removing the pistons, replacing the rings and reassembling same is well within the capabilities of someone who has just successfully rebuilt the brake & clutch MCs.

You can measure (or even see) the amount of clearance created by how the pistons have ovaled the liners. I did not rotate mine, just did rings and bearings... but that was just a quick job to buy me some time. Has 'bought' me 25 years thus far.

I wouldn't get into adding a PCV or blocking that draft tube -- in fact I added a draft tube to my late TR4 just because the pressure seemed to be pushing oil out at every seal. Much better now.
 
That is an excellent picture. I didn't know that you could remove the head without removing the carbs. Alot of the time I spent when I removed the head previously was spent fooling with removing the manifolds in and out. That is very encouraging that it appears not to be necessary.

My never ending follow up question though is if I was to rotate the buckets 90 degrees would I be able to do that delicately enough that I could loosen the above clamping system and NOT have to replace or ruin the infamous Fo8 seal? I have it impressed very deeply in my memory that if that Fo8 seal gets disturbed and fails to provide its sealing function then you are looking at removing the engine to replace that vital seal.

I guess my question is, "Is it possible to rotate the liners as suggested without having to redo the Fo8 seal and remove the engine?"

I don't think my mechanical mojo is ready for engine removal as of yet...though there is always a first time..and stranger things have happened, etc.

Thanks very much,
Jim Lee
 
Hi Lee No the gaskets would be ruined. Think of the gasket as a thin piece of sheet metal about 3/16 wide rusted in place for 50 years. Probably the reason you did not ruin it the first time was that the liners were all rusted/gasket sealed and stuck in place then pinned down to block by the gasket. If you wanted to rotate the jugs/liners which I do NOT think I would do. You would have to pound, hammer, and pry them up from the bottom probably with a chunk of oak and a five pound sledge. Furthermore, it is possible to break them at the thin bottom lip. Again if you want to do an inexpensive ring job you can with the engine in place and the liners unmoved. To be safe you should follow Geo picture and pin the liners down. Just tie back the carbs and manifold and you will have room to work. Sure there is more to do this job right like check sleeve taper and make sure the rings do not pinch, but it just might be the best hundred or so bucks you ever spent.

George
 
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