270 Offy

[tornitore45]

Rough force calculation
Average Vacuum 20" Hg
Atmospheric pressure 30" Hg ~ = 15 PSI
Pressure on the valve 10" Hg ~= 5 PSI

1/4" Valve area 0.25 3.14/16 = .05 sqinch Neglecting the stem.

Force on valve 0.25 Lbs

Kind of low, the spring will certainly pull harder, but than again if the leakdown is good under test conditions it may be better with the spring.

 

[awake]

Terry, what a great idea! The one thing that makes me pause is that in my only build to date, I waited to drill the side entry port until I could drill through the head and valve cage at the same time. Do you run into any trouble drilling the side port before assembly? Do you assemble the valve cage into the head using Loctite?

 

[petertha]

In any case there is a primer that you need to add to the joint that adds the necessary iron to the joint before assembly.

In another post I referenced my experience with Loctite going off appreciably faster in this exact application, bronze valve cages in aluminum head. It was kind of heads up getting them installed rather quick-ish without adhesion kicking in half way through insertion. I wonder if primers accelerate this even more? There wasn't a lot of reference to this accelerated cure time aspect, seems like usually its recommended for more sluggish bond situations.

 

[mayhugh1]

When I leak-check my valves I always apply pressure with my thumb to hold the valve against the seat to simulate the action of the spring. I once estimated this thumb force to be two pounds which is what I typically strive for when choosing the spring rate and installed height of my springs. I usually, but don't always, get a valve to seal well enough to measure an acceptable leak-down time without some thumb pressure. Once the valves are installed in the head, the vacuum can then be pulled through a port as a final check with the springs installed, but you'll now be including any leakage around the valve stem which isn't fair, and sealing this area with the installed spring is much more difficult. Grease on the stem would work but be messy.

If the valve is polished free of machining marks while still on the lathe (easy to do), and the cage properly machined, the leak down time will be a few minutes on the very first try and won't need to be tested anymore. If there are some machining scratches left from the seat cutter, then you'll get an intermediate result and then have to work some to extend the time beyond the ten seconds. I never use the valve to do this (lapping) because the valve typically isn't the problem and I don't want to transfer a seat problem over to a perfectly fine valve. I'll polish the seat using a wood or felt bob and extra fine TimeSaver or metal polish. If the seat requires a lot of work, you stand the chance of changing its geometry some. If the cage isn't yet installed, you have the option of starting over with a new one.

The trick is to not scratch up the seat with the seat cutter. A close fitting pilot lubed with oil and oil on the cutting edges makes the process go smoother with fewer chatter-induced scratches. - Terry

 

[mayhugh1]

Awake,
I too was concerned about drilling the ports through the cages because I'd never done it that way before. The only problem I (actually my thumb) ran into was a poor work hold down scheme, and I wouldn't recommend mine to anyone. I used a 60 degree v-drill so I could do the spotting and drilling in one go. Since my port diameter was .187" In diameter, a standard size cutter was available. - Terry

 

[mayhugh1]

Dave,

Thanks for the Loctite tips. My frustration with Loctite is their bewildering product line with so many choices and subtle differences among them that I'm always left wondering if I'm using the right product and using it correctly. I waded through a lot of Youtube fluff but gave up before getting any real help with my application.

I was surprised at how easy it was to reach an application person at Henkle. (Just dial 1-800-LOCTITE and press '1'.) I learned a lot in the few minutes I spent with a pretty knowledgeable person on the other end. I was told that 620 was still my best choice if I really needed a 400F service temperature. I'm not really convinced that I do and, as you mentioned, there are newer and easier to use products with temperature resistances up to 350F.

I finally understand the active/passive metal stuff. In addition to being anaerobic, Loctite needs free metal ions to kick off its bonding process. Loctite doesn't bond to these ions. They are only used to activate the adhesive. The bonding occurs to the metals being joined, and different metals end up with different bonded shear strengths. The bonded shear strength of aluminum is 80% that of steel, and the bonded shear strength of bronze is 40% that of steel. Numbers on the bonded shear strength of bronze to aluminum weren't available.

Loctite can find the ions it needs on the surfaces of iron, steel, nickel, and copper. Loctite calls these 'active' metals. On the other hand, metals such as aluminum, stainless steel, titanium, magnesium, and black oxide'd or plated parts aren't 'active', and without an activator the bonding process may take days or weeks to occur, or it may never happen. If an active metal is being bonded to an inactive metal, Loctite will find the ions it needs on the active metal surface, and no activator is required. If two inactive metals are being bonded, an activator is required. Although it's also referred to as a primer, it's doesn't work like most of us would think since Loctite doesn't actually bond to it. A Loctite primer is just a copper salt in a fast drying solvent that leaves behind copper ions on the surface it was applied.

A primer can be useful even between two active metals to speed up the curing process especially if there is a big gap or if the parts are cold. The optimum gap for 620 is between .002" and .004". The downside is that if a primer is used, the ultimate bond strength will be 80% of what it would have been with no primer.

I also found out that 620 requires a 24 hour cure at 175F in order to achieve a full-strength high-temperature bond. This was something that my earlier test didn't include. I'm plan to repeat my test with my new found knowledge. - Terry

 

[petertha]

Interesting stuff. So maybe the accelerated cure for aluminum/bronze has more to do with the bronze having abundance of copper (80-90% in most alloys) even though the %Cu in aluminum is small?

 

[mayhugh1]

The problem with aluminum might be the oxide on its outer surface. - Terry

 

[dsage]

Dave,

Thanks for the Loctite tips. My frustration with Loctite is their bewildering product line with so many choices and subtle differences among them that I'm always left wondering if I'm using the right product and using it correctly. I waded through a lot of Youtube fluff but gave up before getting any real help with my application.

I was surprised at how easy it was to reach an application person at Henkle. (Just dial 1-800-LOCTITE and press '1'.) I learned a lot in the few minutes I spent with a pretty knowledgeable person on the other end. I was told that 620 was still my best choice if I really needed a 400F service temperature. I'm not really convinced that I do and, as you mentioned, there are newer and easier to use products with temperature resistances up to 350F.

I finally understand the active/passive metal stuff. In addition to being anaerobic, Loctite needs free metal ions to kick off its bonding process. Loctite doesn't bond to these ions. They are only used to activate the adhesive. The bonding occurs to the metals being joined, and different metals end up with different bonded shear strengths. The bonded shear strength of aluminum is 80% that of steel, and the bonded shear strength of bronze is 40% that of steel. Numbers on the bonded shear strength of bronze to aluminum weren't available.

Loctite can find the ions it needs on the surfaces of iron, steel, nickel, and copper. Loctite calls these 'active' metals. On the other hand, metals such as aluminum, stainless steel, titanium, magnesium, and black oxide'd or plated parts aren't 'active', and without an activator the bonding process may take days or weeks to occur, or it may never happen. If an active metal is being bonded to an inactive metal, Loctite will find the ions it needs on the active metal surface, and no activator is required. If two inactive metals are being bonded, an activator is required. Although it's also referred to as a primer, it's doesn't work like most of us would think since Loctite doesn't actually bond to it. A Loctite primer is just a copper salt in a fast drying solvent that leaves behind copper ions on the surface it was applied.

A primer can be useful even between two active metals to speed up the curing process especially if there is a big gap or if the parts are cold. The optimum gap for 620 is between .002" and .004". The downside is that if a primer is used, the ultimate bond strength will be 80% of what it would have been with no primer.

I also found out that 620 requires a 24 hour cure at 175F in order to achieve a full-strength high-temperature bond. This was something that my earlier test didn't include. I'm plan to repeat my test with my new found knowledge. - Terry

Wow! Great stuff Terry. Thanks for taking the time to share that. I have also found their literature very confusing and after seeing their recent presentations (which I also found confusing) the take away I got from it was to give them a call. I'm glad you did and passed along what you learned. I too have had issues with loctite in some conditions. Even those that (apparently) should have been ok. But I always chocked it up to old product or poor fit up.
Perhaps not clean enough?
I also found out from their presentation they have yet another product line for "not so clean" applications and another that you don't even have to put on the threads before assembly. They say it wicks in from outside and still locks the threads.
It's all sort of black magic. I'm glad you got some guidance.
Please report on the results of your new tests.

Thanks again

 

[awake]

Yes, very helpful information. Thanks for sharing!

 

[mayhugh1]

The Offy's valves started out as a handful of 2-1/2" long blanks that I band-sawed from a 3/8" 303 stainless rod. A valve will be turned on each end of each blank with a half inch work-holding spigot left between them.

To begin, the blanks' ends were faced and center-drilled while keeping in mind the valve stem diameter will be only 1/8". They were then moved to the Wabeco lathe where each valve was turned using a pair of programs. The first (roughing) operation left .040" excess stock for a second (finishing) operation. The blanks were held in a 5C collet chuck with their far ends supported by the tailstock. A 5/32" diameter phosphor bronze dead center was turned and mounted in the tailstock to allow a DCMT21.51 lathe tool to access the entire blank.

Dimensional accuracy wasn't a consideration during the roughing operations which were completed on all the blanks before moving on to the second operation. The goal for this step was to leave .002" excess stock on the stems for manual finishing. With care, the Wabeco will hold a thousandth or so over several consecutive parts, but model engine valves can be tricky. Even with tailstock support, part deflection can be inconsistent and difficult to control. Too little axial force from the tailstock will allow the stem to deflect when contacted by the tool, and a portion of the stem will wind up oversize. Too much force during turning can create wear on the tiny dead center or on the part itself and, in fact, can flare its end. The resulting clearance will again allow part deflection.

The stem diameter was measured at the completion of each finishing operation and, when it seemed appropriate, a correction was applied to the program before the running the next part. The finishing operation was run on all the parts before going on to the manual polishing steps.

The diameters of the valve stems were manually finished with abrasive paper. On several parts that had been wrongly corrected and ended up with 3 or 4 thousandths excess stock, the manual finishing took more time than the turning operations. The stems were polished to their final size (.001" under the valve guide bore) using 400g, 600g, and then 800g paper. The seats received only very light polishing with 600g and 800g paper since the second turning operation left them with the correct geometry and a very fine surface finish. Each stem was continually mic'd during finishing and the final result verified with a test cage. The final polishing was performed with a dab of red buffing compound on a clean shop towel which left the valves with a mirror finish. Each was leak-checked with a test cage before being parted from its blank. All leak times times measured greater than a minute.

After parting the valves from the blanks, their faces were finished while safely gripped in a shop-made PVC split collet. This same collet was used to hold the valves while their stems were being trimmed to their final lengths. Each stem was trimmed for the same height above a test cage. The valves were completed by cutting the .020" wide grooves for the spring retainer clips after which the leak-checks were repeated. - Terry

 

[mayhugh1]

I made two more Loctite tests and got essentially the same results as before. One of the tests included Loctite's 7471 activator, but it didn't seem to make much difference. Henkle told me that would probably be the case since the bronze cages would supply the ions for a cure that aluminum could not.

I allowed both test assemblies to cure undisturbed at room temperature for a full 72 hours before stressing them. In both tests, each bronze slug held tight under a 200 pound load applied at room temperature. I then heat cured the assemblies for an additional five hours at 300F and while still hot, all the pins slipped under the same 200 pound load. The heat cure should optimally have lasted 24 hours, and it didn't occur to me until later that maybe the assemblies needed to return to room temperature to complete the cure. It's also possible, however, that a high-strength high-temperature bond may not be possible between aluminum and bronze. Aluminum's temperature coefficient of expansion is so much greater than that of either bronze or the Loctite itself, that the expansion difference may be a problem.

On the other hand, Loctite's published data for bronze isn't all that different from my results. The shear strength of 680 on aluminum is 80% that of steel and on bronze it's only 40%. My results with aluminum/bronze aren't that far away from their 40% number.

I didn't use an activator when I installed the cages in the Offy's head since it showed no improvement in my test, and according to Henkle it degrades shear strength for all metals by 20%. In order to help install the cages at the same height above the head, I made some tapered Delrin plugs to locate and secure them to the head through the port openings while curing. Before assembly, the aluminum bores were scrubbed with acetone-wetted Q-tips, and each cage was lightly polished one last time using 800g paper to remove any surface oxide that might have formed since they were machined.

A .005" to .007" wide seat was manually cut into each cage and leak-checked with its partner valve just before installation. For some reason, the leak-down time of every valve/cage pair was greater than a minute with no additional work required on any of the seats. Only a few valves required a bit of thumb pressure to achieve a nearly perfect seal. In some hundred seated valves I've installed, I don't recall ever having an issue with a valve, but the seats have always required at least a few minutes of polishing with Time-Saver and/or metal polish in order to pass my leak-down test. For this step I used a dedicated valve or even a felt or soft wood bob for lapping/polishing, but I long ago quit using the actual valve that would end up in the engine.

And so, something about my cage machining process has favorably changed. One difference is that I bored the mouth openings using a tiny boring bar rather than a drill and/or ball end mill as I've done in the past. Another difference is that the Offy's cages are slip fits in the head rather than being 'lightly' press fit.

My seat cutter is a commercial 12 flute 45 degree piloted chamfering tool that I've used in the past and currently available from Midway:

PTG Interchangeable Pilot Muzzle Cylinder 45-Degree Chamfering

This time, instead of using it dry, I oiled the flutes and pilot with 30 wt oil which seemed to make its cutting action much smoother. I was careful to remove all traces of oil from the seat with solvent before performing its leak check since oil on the seat's surface will invariably make it look better than it really is.

The cage installation was completed by drilling and pinning the cages to the head using Loctited steel dowel pins as shown in the photos. This last step was risky although probably needed, and so I made a practice run on my 'mule" head using a couple spare cages and the custom machined angle blocks made earlier. - Terry

 

[bobden72]

I made two more Loctite tests and got essentially the same results as before. One of the tests included Loctite's 7471 activator, but it didn't seem to make much difference. Henkle told me that would probably be the case since the bronze cages would supply the ions for a cure that aluminum could not.

I allowed both test assemblies to cure undisturbed at room temperature for a full 72 hours before stressing them. In both tests, each bronze slug held tight under a 200 pound load applied at room temperature. I then heat cured the assemblies for an additional five hours at 300F and while still hot, all the pins slipped under the same 200 pound load. The heat cure should optimally have lasted 24 hours, and it didn't occur to me until later that maybe the assemblies needed to return to room temperature to complete the cure. It's also possible, however, that a high-strength high-temperature bond may not be possible between aluminum and bronze. Aluminum's temperature coefficient of expansion is so much greater than that of either bronze or the Loctite itself, that the expansion difference may be a problem.

On the other hand, Loctite's published data for bronze isn't all that different from my results. The shear strength of 680 on aluminum is 80% that of steel and on bronze it's only 40%. My results with aluminum/bronze aren't that far away from their 40% number.

I didn't use an activator when I installed the cages in the Offy's head since it showed no improvement in my test, and according to Henkle it degrades shear strength for all metals by 20%. In order to help install the cages at the same height above the head, I made some tapered Delrin plugs to locate and secure them to the head through the port openings while curing. Before assembly, the aluminum bores were scrubbed with acetone-wetted Q-tips, and each cage was lightly polished one last time using 800g paper to remove any surface oxide that might have formed since they were machined.

A .005" to .007" wide seat was manually cut into each cage and leak-checked with its partner valve just before installation. For some reason, the leak-down time of every valve/cage pair was greater than a minute with no additional work required on any of the seats. Only a few valves required a bit of thumb pressure to achieve a nearly perfect seal. In some hundred seated valves I've installed, I don't recall ever having an issue with a valve, but the seats have always required at least a few minutes of polishing with Time-Saver and/or metal polish in order to pass my leak-down test. For this step I used a dedicated valve or even a felt or soft wood bob for lapping/polishing, but I long ago quit using the actual valve that would end up in the engine.

And so, something about my cage machining process has favorably changed. One difference is that I bored the mouth openings using a tiny boring bar rather than a drill and/or ball end mill as I've done in the past. Another difference is that the Offy's cages are slip fits in the head rather than being 'lightly' press fit.

My seat cutter is a commercial 12 flute 45 degree piloted chamfering tool that I've used in the past and currently available from Midway:

PTG Interchangeable Pilot Muzzle Cylinder 45-Degree Chamfering

This time, instead of using it dry, I oiled the flutes and pilot with 30 wt oil which seemed to make its cutting action much smoother. I was careful to remove all traces of oil from the seat with solvent before performing its leak check since oil on the seat's surface will invariably make it look better than it really is.

The cage installation was completed by drilling and pinning the cages to the head using Loctited steel dowel pins as shown in the photos. This last step was risky although probably needed, and so I made a practice run on my 'mule" head using a couple spare cages and the custom machined angle blocks made earlier. - Terry
View attachment 116691View attachment 116692View attachment 116693View attachment 116694View attachment 116695View attachment 116696View attachment 116697View attachment 116698View attachment 116699

Terry could you give me a link for Midway and the 12 flute 45 degree piloted chamfering tool please. Have goggled but can not find them.

 

[stevehuckss396]

There is a. Link in his post

 

[bobden72]

There is a. Link in his post

Ah yes missed that thanks.

 

[petertha]

Really good stuff on the testing info, Terry.
So that I'm clear, is pinning the valve cage on this particular engine because the top of the cage does not dead-end into a counterbore within the head like on other engines? You only have the circumference OD bond area to keep it put?

 

[mayhugh1]

Really good stuff on the testing info, Terry.
So that I'm clear, is pinning the valve cage on this particular engine because the top of the cage does not dead-end into a counterbore within the head like on other engines? You only have the circumference OD bond area to keep it put?

Correct...

 

[mayhugh1]

The valve springs were tackled next so the valves could be assembled in their cages. Their diameter and installed heights have already been defined by the cage geometry. The remaining parameters are dependent upon the force needed to hold the valve closed at the spring's installed height. For this, I selected 2 lbs based upon my experiences with earlier builds. An online spring calculator:

Spring Calculator & Instant Quote - Quality Spring, Affordable Prices

was used to iteratively solve for the rest of the parameters after selecting the wire material and diameter. I used .022" diameter music wire left over from another project, and after a few minutes with the calculator I settled on:

.300" o.d.,
.82" free length, and
4.5 turns .022" music wire.

The calculator predicted a 3.5 lbs/inch spring rate for an acceptable force of 1.8 pounds to hold the valve closed at an installed height of .30". The force required to fully open a valve will be 2.1 pounds.

A .195" diameter mandrel was used to wind the springs on my lathe using a shop-made tool post wire feeder. I wanted an inactive turn on the ends of the springs that I could grind flat so they will sit vertical on their perches and not rub the interiors of the followers. Engaging/disengaging the lathe's power feed to produce closed ends required a lot of practice, and I wasted a shameful amount of wire in the process.

The springs were normalized for 6 hours at 350F in an oven to heal the micro-cracks created by the winding process. They were then tumbled overnight in a vibratory tumbler with walnut shells and polishing compound for a bright finish.

Measurement of the force required to tip each installed valve off its seat agreed very closely with the predicted 1.8 pounds.- Terry

 

[dsage]

Great stuff. I learn something every time you post. I've never heard of the normalizing of the springs. But then I've never had one break either which I assume is the reason you take that step (to avoid breakage) ?
Nice finish. Such attention to detail.
Thanks

 

[mayhugh1]

Thanks, Dave,

The heat treatment step helps the spring retain its spring factor over time.

I used to 'pin shoot' at a local gun range many years ago. This is a handgun competition in which you shoot at five bowling pins while trying to knock them off the back a wide table faster than your opponent. I used a 45 caliber semi-automatic that I specially built to absorb the recoil of a powerful round that I hand-loaded especially for this weekly competetion. The gun used a special recoil spring that I had to hand wind. At the end of each evening of competition, I could feel the spring weakening and it's effect on my time between shots, and so a new one was used for each competition.

After coming across an article on spring making, I learned about the heat treatment step that spring manufacturers use and so I tried it. It increased the lifetime of my gun springs nearly an order of magnitude, and so I continued to use it on all my hand made springs ever since.

My gun weighed 8 pounds and so wasn't legal for national competetions, but it cleaned up locally. - Terry