270 Offy

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tornitore45

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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

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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

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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

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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
 
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mayhugh1

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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

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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

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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

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

dsage

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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
 

mayhugh1

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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

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