Valve Seal Question: Bronze Manganese

[lesingepsycho]

Hello everybody.

I'm still getting a lot of smoke on startup and I've eliminated just about everything except valve seals. I have a few questions about this. Could blue smoke on startup an indication that they are bad? If so, are they difficult to replace? With an air pressure fitting that hooks up to the spark plug hole can they be replaced without removing the head? Are the bronze-manganese guides worth the more than doubled price tag?

Looking forward to reading the replies. Thanks in advance!

JACK

 

[77_MG_Midget]

What kind of motor? The Triumph 1493cc motor doesn't have valve stem seals from the factory, which would indicate worn valve guides. I'm having my valve guides machined to accept an umbrella seal right now. As far as the bronze valve guides, according to the machine shop I'm using (they build high performance engines), they're not worth the expense for a "stock" motor. To the best of my knowledge, blue smoke on startup is usually worn valve guides/stem seals. I may be wrong, but valve stem guides should be replaced by a machine shop, which means pulling the head.

 

[Darwin]

A quote from Calum Douglas' excelent article on building the 1300/1500 motor:

- Slightly Shorter valve guides are fine to an extent to get some of them out the port but go too far and the limited valve>valve stem contact area gives rapid wear and possibly over heated exhaust valves as the heat has a harder time dispersing.
- Use valve stem oil seals, just about every engine on the planet except Spitfire engines use them. They slip over the top of the valve guides. These are Ford Pinto items (UK Ford), available from Canley Classics in the UK. They cost about £12 a set.
You may need to loctite them in place to the top of the valve guide

 

[Matthew E. Herd]

Here's another question for the forum. I've been contemplating (at length) the installation of a harmonic balancer on my 1500 midget. The reason for this potential project is that most cars have had them since the 40's, so I understand. However, the modification of the crankshaft pulley is not necessarily a viable option, because if one wants to pull the engine, the clearance between the crankshaft and the sheet metal panel (I don't know what to call it) where the hood latches, as well as the clearance between the crank pulley and the steering rack, are compromised. After just pulling my engine to replace the transmission, it is my conclusion that it would be very difficult if the balancer could not be removed while the engine is still in the car. I am also concerned about having adequate counterbore to accept the crankshaft nut, assuming the air pump v-belt groove was removed from a stock (later) 1500 pulley. It is just recessed from the outer face, and would stand proud if this groove was removed.

I understand a GT6 rubber damper can be fitted, but I am also unsure as to the availability of such a part, and the word on the street is that a fluid damper is superior to a rubber one (stock starting with the 1275's). However, none is probably inferior to rubber in any case. David Vizard's book on tuning the A-series engine indicates that fluid dampers amount to a few horsepower, as well as a reduction in vibration in the system as a whole. Any thoughts are greatly appreciated!

Matt

 

[Dave Russell]

[ QUOTE ]
The reason for this potential project is that most cars have had them since the 40's, so I understand. However, the modification of the crankshaft pulley is not necessarily a viable option, because if one wants to pull the engine, the clearance between the crankshaft and the sheet metal panel (I don't know what to call it) where the hood latches, as well as the clearance between the crank pulley and the steering rack, are compromised. After just pulling my engine to replace the transmission, it is my conclusion that it would be very difficult if the balancer could not be removed while the engine is still in the car. I am also concerned about having adequate counterbore to accept the crankshaft nut, assuming the air pump v-belt groove was removed from a stock (later) 1500 pulley. It is just recessed from the outer face, and would stand proud if this groove was removed.

I understand a GT6 rubber damper can be fitted, but I am also unsure as to the availability of such a part, and the word on the street is that a fluid damper is superior to a rubber one (stock starting with the 1275's). However, none is probably inferior to rubber in any case. David Vizard's book on tuning the A-series engine indicates that fluid dampers amount to a few horsepower, as well as a reduction in vibration in the system as a whole. Any thoughts are greatly appreciated!

Matt

[/ QUOTE ]
Hi Matt,
In general, the 1500 likely has a mild torsional vibration mode at around 5,500 rpm & a much stronger one somewhere above this rpm. Since the stock engines were unlikely to be run at these elevated rpm's, the dampers were not judged to be needed. You could likely run at the first mode for quite a while without serious harm to the crank. The second, higher mode might be limited to a few seconds. As with all things mechanical, the effects of this stress are cumulative & the crank will eventually fail.

Lightening the flywheel, increasing counterweighting on the crank & making it stiffer, lighter reciprocating weights, & torsional dampers all help to raise torsional vibration frequencies & the rpm limits.

As near as I can tell, you are correct. The viscous dampers are more effective than the rubber dampers but are quite expensive. I have no idea what is available for your particular engine, but would suggest some of the available fixes or limiting rpm. Maybe someone with specific knowledge of your engine can help.
D

 

[Dave Russell]

[ QUOTE ]
Hello everybody.

I'm still getting a lot of smoke on startup and I've eliminated just about everything except valve seals. I have a few questions about this. Could blue smoke on startup an indication that they are bad? If so, are they difficult to replace? With an air pressure fitting that hooks up to the spark plug hole can they be replaced without removing the head? Are the bronze-manganese guides worth the more than doubled price tag?
JACK

[/ QUOTE ]
Jack,
The blue smoke on startup is a definite sign that oil is leaking past the valve guides. Others have suggested remedies. An air pressure fitting will hold the valves in position. However, if you apply enough force to break the air seal the valve will drop.

I personally prefer to stuff the cylinder with small diameter nylon rope & bring the piston up on compression. If you happen to break the air seal, no harm done.

I doubt if the bronze guides are of much advantage unless you are racing the engine. If you can find them, guides made of AMPCO 45 are superior to Mang-bronze. As I said, doubtful if either is needed.
D

 

[Matthew E. Herd]

Dave,

Thanks for the input! I have a rather well tuned 1500, and I autocross it, so I am concerned about maintaining reliability as much as possible. Based on extensive internet reading, I have decided that 6500 RPM is a maximum safe limit, but this is largely based in myth and rumor instead of science. Is there a way to know where the harmonic occurs?

Also, there are (to my knowledge) no damper applications for the 1500 (except a stolen GT6 rubber damper). The method I had planned was to take Fluidampr's model for a GM or other car and adapt it. However, I'd obviously like to do a minimum of modifying (i.e. none) so I could return it if need be. Also, I need to make sure it can actually be installed without interference. While there is some space, I decided that in order to get the engine out, you cannot add more to the end of the crank pulley. Simultaneously, I can't lose the V-belt for obvious reasons, so that is not an option either.

I guess what I'm saying is, how can we take a scientific approach to modification (i.e., so we know we've accomplished our goal without just spending a lot of money ... $400 for an alloy flywheel, approx $400 for a fluid damper, $$ for machining a new crankshaft pulley, and I'm not taking the engine apart at this time). On the plus side, the reciprocating mass has already been lightened a bit. My mechanics of materials course covered failure in some depth, but we didn't address systems of this complexity. I don't know how to assess the effects of resonances, which I assume is the situation at approximately 5,500 and some higher RPM. Perhaps someone could provide some input or some guidance toward an appropriate reference. I've read several engine design and theory type books, but crankshaft design/failure has not been included in any depth. Luckily my summer job is in rotating machinery! Should be a good experience.

Matt

P.S. I'm graduating in a few hours! All I have to do is walk across a stage without running into anything ... wish me luck!

 

[aeronca65t]

Jack:
Just to be clear here: are you sure you have good rings? Smoke on start-up can come from bad valve guides/seals but also bad rings. And it's worth noting that some forms of "creative modification" to the PCV crankcase system can cause this problem. A leak-down test may be useful to determine if rings are good. As an alternative, do a cold and then hot compression test. If you record a large difference between the two, it is often bad rings.
The Mang-bronze guides are nice but not really needed for normal use.

Matt: I am using a slightly lightened flywheel (about 3 pounds removed from the outer area): that's the only physical mod I've done that may help crankshaft longevity (I do renew the rod bearings and thrust washers about every 25 hours). I haven't tried the damper mod that you mentioned, but it is worth looking into. As Dave suggests, I also limit myself to about a moderate 5800 RPM, which I feel is a practical max for these engines due to stroke length and only three main bearings. When the long-stroke 1500 was first develeoped by BL, they ran several cars at top speed (around 6000 RPM) for a period of about 4 hours. All the test cars failed; they "ran" their rod bearings in this trial. BL never really adressed this issue, assuming that most folks wouldn't run their cars this hard. The previous shorter-stroke 1300 Triumph-based engine is much better in this regard and is probably safer for sustained speeds above 6000 RPM.

Oh, and I've seen a number of folks trip during graduations....don't worry; they'll *still* give you the diploma! /ubbthreads/images/graemlins/grin.gif

 

[Dave Russell]

Re: Valve Seal Question: Bronze Manganese - cranks

Hi Matt,
The "real" problem is that the cylinder two & three crank journals are not fully counterweighted. Only the two very ends are counterweighted. This was very common on the lower power engines, wasn't needed & saved money. If you are going for 6500 rpm, a fully counterweighted crank is necessary. You won't find any modern engines, which are designed for seriously high rpm, that are not fully counterweighted. I have seen some crank modifications that actually weld on the "missing" counterweights. The best way to go is a completely different crank that is fully counterweighted. Obviously very expensive. Slightly less expensive would be a crank made of tougher material but without the counterweighting. Center main bearing failure could still be a problem though.

There is a process called "wedging" that removes weight from the rod journal sides of the crank which increases the effectiveness of the existing counterweights. Lighter rods & pistons will help a bit also. Nitriding or Tuftriding the crank will make it harder & less likely to fail. I don't think that the rpm "fail point" can be calculated very easily. Most people either find out the hard way or play it safe. I guess if you were good at installing accelerometers & associated equipment, you might find the serious vibration frequencies/rpm.

Little, seemingly insignificant, changes like grinding the crank journals undersize, as is normally done, can seriously weaken it.

Many of the better torsional dampers are made in two pieces so that you could remove the outer hub as needed. Finding a "bolt on" for your engine may be another problem though. All of these little items would only serve as band aids to the real first problem.

You should have made it through graduation without tripping over anything by now, congratulations.
D

 

[dklawson]

Re: Valve Seal Question: Bronze Manganese - cranks

Not knowing which engine lesingepsycho has, I'm not sure how to respond. If it's the A-series engine in his Midget I feel comfortable saying that for a street engine the cast iron guides will serve you well. I asked these questions when considering a rebuild of my cylinder head. I got endorsements for both types of guides with no clear indication of one being better than the other. As for the guides, the can be replaced with the head in place (I've done it) but don't waste your time with compressed air. Take Dave Russell's advice and stuff the bore you're working on with clean soft rope instead. It works MUCH better (again, I've tried both). The A-series traditionally only has seals on the intake valves. On a high-mileage engine you can also install them on the exhaust valves. This isn't always a good idea on a recently rebuilt head as there is not enough clearance on the exhaust valves to run w/o the little bit of oil that leaks down the exhaust stems.

For what it's worth, replacing the seals on my valves bought me a few months, but the guides were sooo badly worn (badly tapered) that the head simply had to be rebuilt after a short while. Also, make sure you install the later type seals that have the garter spring around their top skirt, the plain rubber seals don't last long at all, particularly if the valve guides are worn. If you're on a tight budget, do the seals now and save your money for a complete rebuild using the iron guides, hardened exhaust seats, and Viton valve guide seals.

 

[lesingepsycho]

Re: Valve Seal Question: Bronze Manganese - cranks

Thanks guys,

I do have a 1275 A-series and what mainly lead to my question is that the moss catalog makes a huge deal about how great the bronze manganese guides are. If i'm going to go through the trouble, I generally like to go with the best parts so I was just wondering if they are all they're cracked up to be.

As far as the rope trick, I had heard of that once before and had forgotten it. That does seem like the best way to go, less room for "oops"es.

Thanks for the advice, /ubbthreads/images/graemlins/cheers.gif

JACK

 

[Matthew E. Herd]

Re: Valve Seal Question: Bronze Manganese - cranks

Hey, I did indeed make it through, and I didn't have any trouble walking either! I also finished my first day at work, and I'm still a bit undecided ... we'll see /ubbthreads/images/graemlins/smile.gif