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Press fitting alloy into steel dimensions?

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stinkwheel
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PostPosted: 20:31 - 15 Dec 2021    Post subject: Press fitting alloy into steel dimensions? Reply with quote

I've bent a third pushrod on my Enfield bullet. I have concluded a large part of the issue is the pushrods are made of cheese.*

The pushrods are made of some sort of aluminium alloy tube with a hardened steel cup and an adjuster pressed over either end.
https://lh3.googleusercontent.com/pw/AM-JKLXuLowSjuAhQ3WQHoQMg7S28qvCgS3jmxDUasPHAyIzpvZqrMMx1JULIC0Y5wGFe6-MjVgAtrNpuFT_ExBC8pRqOBc-NY8NFGYiBFk5kMTVbZvZ4fo3_9S5D_Jpyl_1SLTbL6YF6cyeUB97It4kW82l=w1576-h886-no

My plan is to replace the aluminium with some good quality, named aviation grade stock (7075 T6)**. I'm just getting lost in the various charts, tables and types of fit. I can find good data for an interference fit for steel in steel and plenty of steel in aluminium but I'm struggling to find charts for aluminium in steel.

The aluminium rod is 10mm OD. The "sleeve" that pushes over it is roughly 9.4mm ID (they vary). I plan to measure the individual sleeves then adjust the diameter of the aluminium rod to suit each sleeve (I don't have a lathe so it'll be old-school going slowly with wet and dry). Then rod in the freezer, sleeve heated up and drive them on.

They are only working in compression and they do get hot so they should get tighter as they warm up.

The question. How much bigger in diameter than the steel sleeve does the aluminium rod need to be?

I'm also considering drilling into the ends of the rod a couple of mm, leaving a 2mm wall so it deforms slightly when it bottoms out in the sleeve. Good idea or stuipd idea?

* I've gone through most of the other failure-modes I can think of including valve springs coil binding, fouling the tappet at full compression, valve impinging on piston, hydraulic locking inside the tappet, valve guide seizure and valve float at high revs making the rod jump the tappet. I think the conclusion is it's either backfiring on startup (hopefully now fixed, I've removed the electronic random spark generator and put points back on) or simply that the rods were made in India for a 17bhp bike and I've got them in a 40bhp bike with hot cams and heavy valve springs and they are exceeding their design tolerances.

**I tried to source some 10mm chromoly tubing but it's like rocking horse poop.

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WD Forte
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PostPosted: 20:51 - 15 Dec 2021    Post subject: Reply with quote

I'd probly start looking up the coefficient of expansion of Wenslydale
err I mean aluminium and steel
I know it's in distance per degree but thassal off hand

I'd also carefully measure the diameter of the push rods at
room temp and after 8-12 hours in the freezer ( -18C ish?)
This could help when selecting the tubing

I'd also do similar test by heating & measuring the tube expansion
to get some real world dimensions
This may help get good results and save time and frustration


OR
would getting some steel push rods made up be that bad a thing?
they're heavier obviously but does the RE rev so high that
the increase in mass would have a significant negative effect?
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Last edited by WD Forte on 20:59 - 15 Dec 2021; edited 1 time in total
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Pete.
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PostPosted: 20:58 - 15 Dec 2021    Post subject: Reply with quote

Interference fits are normally approx. 2 thou per inch so at 10mm you're looking at 1 thou of interference or a bit less.

I'd be tempted to turn it to a slip fit, knurl it up and press it in with bearing retainer. It ain't ever coming out then. Or if you want to order the material and send all the bits to me I'll do the machining for you.
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WD Forte
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PostPosted: 21:07 - 15 Dec 2021    Post subject: Reply with quote

It also occurs to me that at that length (200mm by the look of it)
On contact the hot tube will cool/shrink and rod heat/expand as you
fit them together and may possibly make it a tricky old job.
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Pete.
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PostPosted: 21:21 - 15 Dec 2021    Post subject: Reply with quote

WD Forte wrote:
I'd probly start looking up the coefficient of expansion of Wenslydale
err I mean aluminium and steel
I know it's in distance per degree but thassal off hand

I'd also carefully measure the diameter of the push rods at
room temp and after 8-12 hours in the freezer ( -18C ish?)
This could help when selecting the tubing

I'd also do similar test by heating & measuring the tube expansion
to get some real world dimensions
This may help get good results and save time and frustration


OR
would getting some steel push rods made up be that bad a thing?
they're heavier obviously but does the RE rev so high that
the increase in mass would have a significant negative effect?


The coefficient of expansion isn't such a big deal at that size. A 10mm ally rod will grow 0.0133mm (half a thou) with a 60 degree increase in temperature. So a 1 thou press fit at 20 degrees would not come loose until -100 DegC
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stinkwheel
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PostPosted: 22:06 - 15 Dec 2021    Post subject: Reply with quote

Pete. wrote:
Interference fits are normally approx. 2 thou per inch so at 10mm you're looking at 1 thou of interference or a bit less.

I'd be tempted to turn it to a slip fit, knurl it up and press it in with bearing retainer. It ain't ever coming out then. Or if you want to order the material and send all the bits to me I'll do the machining for you.


That would probably be easier to do. I've got some permabond A1046 (green bearing fit). Maybe I'm overthinking this because if it's a tight fit at room temperature, it will always be tight because the aluminium will expand more rapidly than the steel collar it's inside when it heats up.

7075 10mm aluminium solid bar is nearly half the weight of 4130 10mm dia x 2mm wall steel tube. And I can source it.
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Pete.
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PostPosted: 23:56 - 15 Dec 2021    Post subject: Reply with quote

When you thin the ends don't leave a sharp inside corner, even a tiny radius is preferable.
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stinkwheel
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PostPosted: 00:09 - 16 Dec 2021    Post subject: Reply with quote

Pete. wrote:
When you thin the ends don't leave a sharp inside corner, even a tiny radius is preferable.


Gotcha. I was going to get the fit then gradually taper it out to the main diameter over the next half inch or so. Then polish them.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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Pete.
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PostPosted: 00:47 - 16 Dec 2021    Post subject: Reply with quote

I would not do that the end socket needs to stop against a shoulder. If you make a shallow taper the end piece will get hammered up the taper over time causing the clearances to change. You could rely on the end bottoming out in the socket but how are you going to know that it's bottomed out unless there's a drilling to let the air out?

The proper way is to set the dead length by locating it with a shoulder to seat against.
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virus
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PostPosted: 19:19 - 16 Dec 2021    Post subject: Reply with quote

I think petes covered everything pretty well there as usual. Thumbs Up

At work we do a few different fits including dovetailing and knurled interference fits etc. I think for what you need it to do I wouldnt worry about dissimilar temperature expansion, it will be negligible at that size.

Id be doing a 4 thou interference fit with a shoulder, making sure that its resting on the shoulder not the actual end of the bar like Pete has said that way you can inspect the fit periodically with no issues.

What ID, OD and length of pocket is there in the steel part out of interest?
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owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.
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stinkwheel
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PostPosted: 00:47 - 17 Dec 2021    Post subject: Reply with quote

virus wrote:


What ID, OD and length of pocket is there in the steel part out of interest?


Haven't measured it up properly yet but the ID is in the ballpark of 9.4-9.5mm. Pocket is approximately 10mm deep. One is tapered out from roughly 10.5mm OD to approximately 13mm OD, the other end is a 13mm hex.

I heated the ends of one rod and removed them (by literally pulling them off with a pair of pliers, I could have used my fingers if it hadn't been hot). It honestly looks like it's been turned down to slightly oversize, had a slight chamfer ground onto the end of the rod then been hammered/pressed in until it bottomed out against the shoulder. The adjuster end (with the hex) has the residues of some sort of brown fitting compound on it, the tapered end looks like someone took four or five longitudinal gouges out of the surface of the alloy with the tip of a file or a scribe then pressed it in.

I had an idea, assuming the socket is actually 9.4mm, that I could run an M11 x 1.5 die down the end of the rod, dress the shoulder end with a fine burr/file so the final turn lands up square then sand off the threaded section with fairly course abrasive until the thread is barely visible, then fit with heat and green bearing fit.

It's not seeing any real tension or rotational forces, just compression (and apparently, slight bendfing!), I just need the ends to stay on.

I've got a bit of extra bar and three bend pushrods so I can have a practice fit first.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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virus
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PostPosted: 18:32 - 17 Dec 2021    Post subject: Reply with quote

I cant see why that wouldnt work, I think Id try and hand file a left hand thread simmilar to suit if I were going that way though, think of the Die thread being half of a knurl and you putting the rest in with a needle file. That should give the retaining compound a bit more to pocket into. As you say, at least youve got a few get out of jail free cards, and 10mm of press fit thats in constant compression doesn't sound likely to fail to me.

P.S, I was going to ask why you have an M11x 1.5 die but then I remembered that the Enfield's are made of all sorts of bullshit thread forms Laughing
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stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.
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Islander
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PostPosted: 19:29 - 17 Dec 2021    Post subject: Reply with quote

virus wrote:
I cant see why that wouldnt work, I think Id try and hand file a left hand thread simmilar to suit if I were going that way though, think of the Die thread being half of a knurl and you putting the rest in with a needle file. That should give the retaining compound a bit more to pocket into. As you say, at least youve got a few get out of jail free cards, and 10mm of press fit thats in constant compression doesn't sound likely to fail to me.

P.S, I was going to ask why you have an M11x 1.5 die but then I remembered that the Enfield's are made of all sorts of bullshit thread forms Laughing


I've used Loctite's bearing retainer to sort out a problem with a bearing rotating in the housing of a rear wheel - no slop just no longer a tight fit. It's shown no signs of shifting at all. It's phenomenal stuff. Thumbs Up
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stinkwheel
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PostPosted: 19:37 - 17 Dec 2021    Post subject: Reply with quote

I actually bought a die. I went cheap on the basis it only has to survive four small cuts into alloy. Cheaper than a knurling tool! I looked down the thread charts to see what had a minor diameter closest to what i wanted

I might use it another time to put a random oddball thread on a bike just to fuck with the next owner. I've done it before, the main engine mounting bolt on the last enfield I sold is a UNF.

Enfield do it too. I'm sure it's just to fuck with people. There are three M7 nuts on bullets, holding the alternator stator on. They made studs with cycle thread on one end and M7 on the other. They also used an M11 fine on some of their petrol tank fuel tap couplings.

Hitchcocks make an adaptor to fit larger amal concentrics to 500 bullets, their studs are M8 into the head and a cycle thread nut. I know why they did it, because there is limited clearance and the cycle thread nut they used has a smaller hex but they could have just used JIS M8 nuts which have a 12mm hex (which is what I did to fit the manifold for my big mikuni).
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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virus
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PostPosted: 20:19 - 17 Dec 2021    Post subject: Reply with quote

Islander wrote:

I've used Loctite's bearing retainer to sort out a problem with a bearing rotating in the housing of a rear wheel - no slop just no longer a tight fit. It's shown no signs of shifting at all. It's phenomenal stuff. Thumbs Up


Yeah ive used Loctite 660 to repair a keyway on a crankshaft that was uneconomical to repair, im amazed at how well it held the key in place once set and that engine has over 50k miles on it and climbing since that repair too. Sometimes you just need the right magic goo Laughing

Stinkwheel wrote:
They made studs with cycle thread on one end and M7 on the other.


Aye thats exactly the sort of bullshittery I remember you saying Enfield liked doing last time we were pissed around a fire.

It is you duty to put some M11 thread somewhere on the next bike you plan on selling now. Even if its just to get your moneys worth out of the Die.

One of the companies my employer subcons for like to invent their own threads so people have to go to them for spares. They once asked our quotes dept if we could make them a M16.5 x 1.75 thread... even though our CNC lathes wouldnt have a problem making it they were politely told to stop being silly cunts. Laughing
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owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.
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Nobby the Bastard
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PostPosted: 20:28 - 17 Dec 2021    Post subject: Reply with quote

Fuckwitterey is a more apt than bullshittery but that depends on the application.
Enfield is the former, your customer sounds more like the latter.
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stinkwheel
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PostPosted: 21:41 - 17 Dec 2021    Post subject: Reply with quote

virus wrote:

One of the companies my employer subcons for like to invent their own threads so people have to go to them for spares. They once asked our quotes dept if we could make them a M16.5 x 1.75 thread... even though our CNC lathes wouldnt have a problem making it they were politely told to stop being silly cunts. Laughing


You should suggest they start using Whitworths, then at least they will be sound from an engineering point of view and most people wouldn't have the first idea what they were looking at anyway. Or start the great BA threadform revival?
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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virus
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PostPosted: 22:17 - 17 Dec 2021    Post subject: Reply with quote

stinkwheel wrote:


You should suggest they start using Whitworths, then at least they will be sound from an engineering point of view and most people wouldn't have the first idea what they were looking at anyway. Or start the great BA threadform revival?


Oh this customer has been around since the 40s or so, they wanted to switch to some metric bullshit none existant thread because their customers started to finally find suppliers of Imperial fasteners Laughing
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stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.
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stinkwheel
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PostPosted: 23:52 - 04 Jan 2022    Post subject: Reply with quote

Tried a few things on "scrap" alloy (ie not the 7075). The thread cutting was trickier than I thought, couldn't get it started straight enough and finished on a neat enough line, even with the piece in the drill press and the die in a drill vice.

Here's what I came up with. I slotted some 10mm ID steel tube and de-burred the inside edges to give me two tools. The longer split piece is effectively a collet so I can grip the piece in a drill chuck without marking it. The shorter, partially split piece is a distance stop to clamp on at the line where I want the step. Some masking tape on there for extra grip and safety.
https://lh3.googleusercontent.com/pw/AM-JKLVoy6rV-MRRNhW0_1Awrf52wkWmYc2mefEG12bZ0IqUpnvoQMxrbHAHRbwGNK_KoGo0ydkbWLJnEu-PJJ6ymeC9EiGdYIJLX60MIZMLssVzGAljr12Ljk-0s4DtwrXFXaxtwvKe7LOBIS9ARQ1-J0nH=w1576-h886-no

https://lh3.googleusercontent.com/pw/AM-JKLWGUfOeDYAMTSMn_bjBLG8BgK_OdYd2qsmTNjn0WUqVCyvWj_rmcfVWsgB-4EgG6seQdIZ2jDRvnEEfIXtRFFR2WrrdriFEAQNLfSbTsefUMKm00Q7XxTyUQuSyeaT2guX6hT8U0evx7OCBD2ia96d_=w1576-h886-no

Then I chucked it up in the drill press and with it at a low speed, made horizontal strokes with a second cut file along the bottom using the edge of the distance stop to set the depth. I considered grinding a "safe" edge on the file to butt against the stop but it wasn't removing a significant amount of material from the steel.

I did have to support the piece with a gloved hand to get enough force without bending it too much.
https://lh3.googleusercontent.com/pw/AM-JKLUS8siabaWBxCVo1kTUENePYzgr_hAq67nhp70geIYgDUZlKHxsd3fmaR_3P2Cj65UwxVBhE75UMSYFqFcQLhGuHIDsthdtZTFUDw8DQPQw3Az43oj9c-mMCtUjRGnOcUtS9_Uep22SMJugGe6Ew6Ak=w499-h886-no

I did ten file strokes then measure, then as I got closer, dropped it to 5 then using lighter strokes. Considered dropping to a third cut file but figured the texturing was probably going to be helpful for getting a good bond. I'm quite pleased with how even the file cuts are.

Here's the result.
https://lh3.googleusercontent.com/pw/AM-JKLWjGEP-hcUBk8khJTksqTqBfLOVKpJ_LvOsul5cPB20gLk2mEj5yTN7GqvbKfjzNkNnE54nyfxS6IAYygys-T-Svh1Xj7B0tyrwC4T2tUJ9EZWf_43QcW5uDqExnOy7Ox8XGu2ov6_wGuEVokaLaYdI=w1576-h886-no

Then pressed the ends on using a sash-clamp and green bearing fit.
https://lh3.googleusercontent.com/pw/AM-JKLWzT8tuAh2TSvQYOg_EYFtNrdjTccmHa_M_qlEjw78SCLCclsI_sfDuTygWjV84Eo4u6QREpSWtqVJgaFtq-eC0Q9UHtnfvp5OIkPo7ju33knBAtWQPjX7ICGLRmxJFS4yJ92qrn749fbxs7pFOVYHq=w499-h886-no

I did have an isse with the non-adjuster end. Butting it against the step was probably the wrong choice here. I think it needs to butt against the end and come down to flush with the step because the steel end tapers to a point. I split two of them on fitting.
https://lh3.googleusercontent.com/pw/AM-JKLUjPDlZVrH_y9aT1XbKjiU81fM-MogGCcCcAQfw85mkv_lE5kd1znbmBVAr9xHstISZR0TCTmlU5EK7wtOQ0dhOqMG-MZgXzIVAzdVE0Q6eXxmAubQENTyC47CD0p1Mn5HbQLfZzM6CrWpD7X757mk1=w1576-h886-no

I've now found a different type of end which doesn't come to a point like that so i'll wait for them to arrive before going any further.

Original on the left, mine on the right. There is a 20g difference in weight but the one on the right is solid 7075 bar, the one on the left is hollow tube of unknown grade. I made it 2mm longer becaue i've fitted an extra 2mm compression plate.

https://lh3.googleusercontent.com/pw/AM-JKLVQ0M0cnOulvg3cvQIlPSgNoUVt4V-EN2YNDH1VKvhqzpb8Ui6BxOJmKQ3eGzxZl2Thq0fhEnOe-5LQyentjXzJKJ8Q_Q0YioLoNjtPw_fttFWq7Fd6BmH1rIMkQQVJ1CRH9qMGCXiwbesct808PQxg=w499-h886-no

I did also have to drill into the adjuster end of the bar because the threaded adjuster that screws in goes up inside the rod about 10mm. I achieved this by making a drill guide from a block of alloy with a 3mm pilot hole then a 10mm hole part with into it. Slotted the bar into the 10mm hole then drilled my pilot dead centre using ther drill guide. I then opened the guide out to 5mm for the M6 adjuster thread. Next I fitted the end on the rod and ran a tap down it so the thread continues into the alloy from the adjuster. That way, when it's screwed in, it will be engaging with both the adjuster and the rod. I forgot to take pictures of this.
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jeffyjeff
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PostPosted: 03:59 - 07 Jan 2022    Post subject: Reply with quote

To echo WD Forte's thoughts above, have you figured the delta in coefficient of expansion? Seems the solid pushrod (having more mass) might expand more than a hollow pushrod of the same length. I don't know how you would estimate the pushrod's operating temperature, sump oil temperature might get you in the ballpark, but could be tens of degrees cooler than the pushrod temp.

At any rate, on assembly, you might consider adjusting the valves toward the loose end of the range, and play with the clearance as the engine breaks in. just a thought.
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A100man
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PostPosted: 13:05 - 07 Jan 2022    Post subject: Reply with quote

All I can say is that (classic) RE owners are a dedicated bunch..
..foolhardy, but dedicated. Wink
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stinkwheel
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PostPosted: 14:09 - 07 Jan 2022    Post subject: Reply with quote

jeffyjeff wrote:
To echo WD Forte's thoughts above, have you figured the delta in coefficient of expansion? Seems the solid pushrod (having more mass) might expand more than a hollow pushrod of the same length. I don't know how you would estimate the pushrod's operating temperature, sump oil temperature might get you in the ballpark, but could be tens of degrees cooler than the pushrod temp.

At any rate, on assembly, you might consider adjusting the valves toward the loose end of the range, and play with the clearance as the engine breaks in. just a thought.


Good point. The simple solution will be to set the tappets cold then check the rods can still be spun on their seats when hot.
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jeffyjeff
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PostPosted: 15:08 - 07 Jan 2022    Post subject: Reply with quote

[quote="stinkwheel"]
jeffyjeff wrote:
The simple solution will be to set the tappets cold then check the rods can still be spun on their seats when hot.

Good idea!
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Hong Kong Phooey
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PostPosted: 15:48 - 07 Jan 2022    Post subject: Reply with quote

I know nothing about the RE engine architecture, but presumably it's ancient and cam operates pushrod which is direct to rocker arm then valve. Cam likely gear driven than chain, so timing is probably not the cause.

In that case a cheesy rod would be an issue on any engine using the same spring rate wouldn't it, regardless of cc?

Unless the higher output engine revs higher, and requires a dual valve spring or uprated set to mitigate against valve float.

If that's the case I'd expect more owners to have complained.

If the rods were intentionally designed to be sacrificial, what's the next weak link in the chain, rocker arm?
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stinkwheel
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PostPosted: 16:21 - 07 Jan 2022    Post subject: Reply with quote

Hong Kong Phooey wrote:
I know nothing about the RE engine architecture, but presumably it's ancient and cam operates pushrod which is direct to rocker arm then valve. Cam likely gear driven than chain, so timing is probably not the cause.

In that case a cheesy rod would be an issue on any engine using the same spring rate wouldn't it, regardless of cc?

Unless the higher output engine revs higher, and requires a dual valve spring or uprated set to mitigate against valve float.

If that's the case I'd expect more owners to have complained.

If the rods were intentionally designed to be sacrificial, what's the next weak link in the chain, rocker arm?


Cams are gear driven off the crank. A follower runs on the cam which pushes the pushrod which bears against the rocker then valve.

The higher output engine revs significantly higher (about 1,000rpm higher and peak power is up in that extra rev range), the cams have significantly higher lift to the point the engine casing had to be machined out to accommodate them and it's fitted with significantly stronger valve springs with wider spacing to avoid bounce and becoming coilbound. So it's fair to say, the rods are under a great deal more stress than in a standard engine. The pushrod adjuster screws have been known to let-go on the standard motors, these have been upgraded but I have bent a couple over the years.

Yes rocker arm would probably be the next thing to let go, but I have upgraded those too. Thinking about it, the 1/4" cycle thread studs that hold the rocker block onto the head would probably also be in the firing line for stripping out of the head leading to the rocker blocks moving up and down, although that would be a relatively "safe" failure mode.
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