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RE: Stripped threads on OS 46AX Engine Head - 12/5/2012 9:40 PM   
RiverLarry


 

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From: Newaygo, MI, USA
Status: offline 		  + 1  ON YOUR SIX     same thing at the field when some one needs a new glow plug  and you tell them  the COST   right on the back of the

PACK !!!    and they say  I can get one from  H/K for $5.00     THEN GO HOME AND ORDER ONE       I was selling it to them for the same thing
I paid for it !!!!!   should of  added $1.00 to it !!!   CANT WIN       R/L

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RE: Stripped threads on OS 46AX Engine Head - 12/5/2012 9:41 PM   
tiffitech


 

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Status: offline 		Hmm...that looks like that the insert has an outer thread that's screwed into the head (and glued additionally).
That's not the best solution but will probably work.

A better way for this is an insert that has an outer shape like an upside down "T" with the shaft of the T shorter than the flesh from the head
so that an screwed in Glowplug will fasten the insert additionally. This has to be made with an tight fit to the head and secured with an pin from above.

Regards,

Holm

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RE: Stripped threads on OS 46AX Engine Head - 12/5/2012 10:42 PM   
aspeed


 

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Status: offline 		See Post  #7  Timeserts.  They have a shoulder so they don't screw in too far, and they expand when screwed in.  They aren't too expensive either after the initial shock of the first kit purchase. $13 for 5.  I have also seen a head in my shop somewhere that had a knurl on the brass insert.  It looks like it was pressed in from the top, but may have been cast in too.  I can't remember what motor it was from right now.  I think the original poster did pretty good on his repair in the end.

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RE: Stripped threads on OS 46AX Engine Head - 12/5/2012 10:56 PM   
Ernie Misner



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Status: offline 		Using some fine grit paper or emery cloth you might try smoothing any sharp edges on the inside of the head. Perhaps not a big deal but would be more critical on a gas engine that runs at higher temps.

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 12:11 AM   
Propworn


 

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Status: offline 		The brass plug installed in an aluminum head may change the heat requirement of the engine. The smaller the combustion chamber the more effect it will have. Brass will hold the heat far longer than the aluminum it replaced. If by chance you seem to have a harder time adjusting the carb especially if the needles seem fussier or the engine runs hot try a colder plug the brass insert may be raising the cylinder head temp just enough to give you fits. We had a piped JETT .25 that blew a plug right out of the head threads and all. The fellow may have over tightened it. We used a brass plug and it would not run consistently on the recommended Merlin plug. It was either to rich and would not peak out or if it did it soon would show signs of overheating. Tried hotter plugs and it got worse went to a colder plug and it ran fine. Tried that plug in the other Jett .25 (because it was locally available not like the Merlin) and it just did not work. We replaced the head over the winter and had to go back to the Merlin plug. Not very scientific but the only difference was that insert.

Dennis

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 1:01 AM   
aspeed


 

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Status: offline 		I often wondered if an aluminum head/button was the best to use.  A steel, or brass, or ceramic one may give better characteristics.  Sounds like the brass holds the heat in better.  Brass may improve the idle on some motors, or have some good effect.

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 12:05 PM   
tiffitech


 

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Status: offline 		@aspeed: No, not meant it this way. I meant to insert the insert with the shoulder from bottom, from the piston side. This way the Glowplug
fastens the insert trough pulling it to the top. No outer thread on the insert (bad for the thermal contact).

Regards,

Holm

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 4:24 PM   
Propworn


 

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quote:

ORIGINAL: tiffitech

@aspeed: No, not meant it this way. I meant to insert the insert with the shoulder from bottom, from the piston side. This way the Glowplug
fastens the insert trough pulling it to the top. No outer thread on the insert (bad for the thermal contact).

Regards,

Holm


From the inside of the combustion chamber? How’s that supposed to work when you only have a few threads of thickness to work with? There isn’t enough material to leave a lip of aluminum to pull the plug against. How are you going to match the shape of the combustion chamber with the inserts flange. The shape greatly effects the propagation of the flame pattern and if you change that you change the characteristics of the engine. Even if you were to thread it in you would have to use a left hand thread as tightening the plug would attempt to turn the plug back out to fall into the combustion chamber. Sir you obviously have never tried this or you would realize it’s just not feasible or cost effective.

Dennis

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 5:05 PM   
aspeed


 

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Status: offline 		A Timesert might work from the combustion chamber side.  The insert kit has a counterbore included.  Still, the washer from the plug wouldn't be sealing on a flat surface at the position it needs, much like a Helicoil. A Timesert from the top looks like about the best to me because it spreads the bottom of the thread much like a rivet, so it will seal and lock too.  A plug like the original poster ended up using is ok too if it doesn't move.

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 6:31 PM   
drac1


 

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Status: offline 		Heli coils are the best option. They lock in, will not unwind and will last forever.

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 7:30 PM   
tiffitech


 

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Status: offline 		@Proworn & aspeed: This isn't my idea, I have a book where this is illustrated, will search that book and make a picture. (B. Krause, Modellmotorentechnik). This Book is about Model Engines and the repair of them.

@Propworn: You have the exactly the thread length of the glow plug as flesh, this is enough for that job. No Problem for the combustion chamber shape,
I have a lathe, just press the insert in, mount the head in the lathe and resurface the Chamber shape, that's all.

I've got an as new looking Bluebird engine a year ago with an stripped Glowplug thread and I wanted to repair it this way.
Before I could do this, a friend came with an Helicoil kit and so I repaired it using this. Haven't run this engine jet.

I do have had bad experiences with Helicoil inserts on Motorcycles, saw more than one stripped out coil in the past (not my bikes) and so I'm
prefer the old fashioned way with an bush type insert. I can't look for that book before saturday, so please be patient.

Regards,

Holm

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 9:13 PM   
Propworn


 

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quote:

ORIGINAL: tiffitech

@Proworn & aspeed: This isn't my idea, I have a book where this is illustrated, will search that book and make a picture. (B. Krause, Modellmotorentechnik). This Book is about Model Engines and the repair of them.

@Propworn: You have the exactly the thread length of the glow plug as flesh, this is enough for that job. No Problem for the combustion chamber shape,
I have a lathe, just press the insert in, mount the head in the lathe and resurface the Chamber shape, that's all.

I've got an as new looking Bluebird engine a year ago with an stripped Glowplug thread and I wanted to repair it this way.
Before I could do this, a friend came with an Helicoil kit and so I repaired it using this. Haven't run this engine jet.

I do have had bad experiences with Helicoil inserts on Motorcycles, saw more than one stripped out coil in the past (not my bikes) and so I'm
prefer the old fashioned way with an bush type insert. I can't look for that book before saturday, so please be patient.

Regards,

Holm


I don't care what any book says you never place anything in a combustion chamber of an aluminum cylinder head from the inside out where under the right conditions it may drop into the engine. Aluminum has a thermal expansion co-efficient of almost twice that of brass, bronze, copper and steel. That means the hole under a rise in temp will expand faster and greater than the material you are using for a plug. The diameter of the glo plug seat is so small compared to the thread diameter there is almost no material to hold the insert in place. The thinness of the head would only allow a very short insert if you were to leave aluminum for the glo plug to seat against. I have enough experience to be able to tell you that you are flat out wrong that it is a good way to make a repair. As to your lathe I doubt you would have much luck trying to center and machine this head by gripping the fins. You would have to use a 4 jaw chuck and indicate everything. You have never done this before and have never tested a repair done this way. You quote from some obscure model book of how someone once made a repair this way and say it’s the best way. BULL you are misleading everyone with your lack of knowledge. As someone else has said a helicoil is the best way to facilitate the repair. Simply proven by how many there are out there running. I know of at least a dozen or so I have personally done and I can only guess how many Clarence Lee has done over the years.

Dennis

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 9:28 PM   
tiffitech


 

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Status: offline 		It seems to me that you know all things. You know all about me, my machines, what I'm done and what not, how to trust books you don't ever read, in short: you know all.

The sentence "Oh my Good" gets now a new meaning for me...

Regards,

Holm


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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 10:51 PM   
Propworn


 

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quote:

ORIGINAL: tiffitech

It seems to me that you know all things. You know all about me, my machines, what I'm done and what not, how to trust books you don't ever read, in short: you know all.

The sentence ''Oh my Good'' gets now a new meaning for me...

Regards,

Holm



Not nearly all things Holm but engines and machining I have 40 years experience as a tradesman and as many as a hobby. I have served my apprenticeship as an automotive machinist then the natural progression was to mechanic and I am finishing my career as a 30 year tool and die/machine repair at Fords of Canada. I have a small tool room in my garage consisting of a 36 inch gunsmith’s lathe and a cnc knee mill and a tig welder.

Through all these years I have been an active participant in the model aircraft hobby. So yes I can claim a little first hand knowledge on the subjects we are discussing. I am not saying what you have seen in the book cannot be done and most likely has been done but it is not close to being the best solution to the problem.

This video I am turning a cylinder for a 1/4 scale Kinner Radial



This is my cnc mill cutting the link rods for the same engine.


< Message edited by Propworn -- 12/6/2012 11:39 PM >

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RE: Stripped threads on OS 46AX Engine Head - 12/6/2012 10:57 PM   
drac1


 

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Status: offline 		I agree with Propworn regarding the co efficient of heat expansion of the different types of metals and the effect that would have on a brass bush pressed into a aluminium head. It is a fact that can not be disputed.
It is not a good idea. Like i have said before a heli coil would be the best way to repair the head.
I have been a first class machinist for 25 years and could quite easily set up the 46AX head in a lathe and machine it to accept the bush. But my experience tells me that isn't the best way.
A "T" bush with the head of the bush inside the engine is definitely not the way to do the repair and is just asking for trouble.
Reading something in one book and taking that for gospel is also not a good idea. You can't believe everything you read is the best way.
As for not using heli coils because you have seen them pulled out on other equipment? Well you have to be very rough to do that. That would not happen under normal conditions, unless the repair was not done correctly.
I quite often insert heli coils into aluminium products as part of the original manufacturing process, because it much stronger than threaded aluminium.

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 6:20 AM   
Ernie Misner



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Status: offline 		Does anyone remember when a lot of guys were drilling a 2nd hole in motorcycle heads, heli coil, and installing a compression release, or Jake Brake??? What a funny sound they made and would slow you down going into a turn without locking up the rear tire. Oh, can't you just see a 50cc gasser on a down line and hit the Jake Brake?.....

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 8:04 AM   
tiffitech


 

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Status: offline 		I don't want to get CNC equipment at all, there are friends here with such things ( I'm a programmer/electronican in my profession).
I own a simple german made, 60 years old mechanican late, grinders, a machine saw, a precision drill press, self made WIG and an indusrial MIG/MAG welder, spot welder and some other stuff. Enough for me.

As for the thermal expansion difference of aluminum and brass: Every brass or bronze bush in a conrod is falling out when it is getting hot?

Helicoil is the cheapest way to repair a stripped head, that's all.

Regards,

Holm

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 11:45 AM   
Propworn


 

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quote:

ORIGINAL: tiffitech

I don't want to get CNC equipment at all, there are friends here with such things ( I'm a programmer/electronican in my profession).
I own a simple german made, 60 years old mechanican late, grinders, a machine saw, a precision drill press, self made WIG and an indusrial MIG/MAG welder, spot welder and some other stuff. Enough for me.

As for the thermal expansion difference of aluminum and brass: Every brass or bronze bush in a conrod is falling out when it is getting hot?

Helicoil is the cheapest way to repair a stripped head, that's all.

Regards,

Holm



Bud you do what you want. Good luck to you. Just quit coming off as an expert when you know nothing of what you speak. Your last quip about connecting rods confirms what I suspected all along. I am one of the eight machine repair personnel in the connecting rod department at Essex Engine Plant in Windsor Ontario. If you even had a tiny bit of sense you could figure out first of all the press fit and area of contact makes up for the difference in thermal expansion when using aluminum alloyed connecting rod. On top of that most connecting rods are not aluminum but some ferrous alloy which has a lower co-efficient of expansion than the bushing. Let me know if you need this explained in detail I think the others get it. You are absolutely, beyond a shadow of doubt one of the most ill informed wrong thinking people I have ever had the chance to converse with. Not worth wasting any more time on. I hope no one is naive enough to take any of your advice seriously. Now as a great man once said "Go away little boy you bother me".

Dennis


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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 1:50 PM   
CrashedTrainer


 

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Status: offline 		hmmm...

as i told you guys already that i got the head back... i put it back on the engine today...i know that there is a gasket that comes in between the engine head and the engine... is it the one in dark brown/copper color seen in the engine head underside photograph that i earlier posted? i think that is the gasket but i couldn't remove it easily..i didn't tried too hard since i dont have a spare at the moment and so didnt want to damage this one... i think its stuck in the engine head gasket groove due to old castor oil

anyways... so i put the head back...@aspeed: before putting it back i installed the glow plug on the head to check if it was flush or not... it was not

i tried to start the engine for more than thirty minutes trying at different throttle openings and needle valve settings including those on which the engine would always start but i couldnt start it....

Q- Could it be becuase of the glow plug not being flush with the engine head due to lengthier glow plug hole now? it is at least 1mm short at the moment I think i need a longer reach glow plug now as suggested by MrCox? does OS make it? if not which brand to use?
Q- i dont think the engine head gaslet is leaking but what is the best practice hear for these gaskets?

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 3:39 PM   
asmund


 

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Status: offline 		Talk about arguing over nothing really, I would just put in a plug and run the damn engine, I bet it will run fine the way it is now

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 4:16 PM   
aspeed


 

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Status: offline 		If it doesn't start, see if it is holding the compression for at least a few seconds first.  If it isn't leaking away you are likely ok.  Most long reach plug motors that I have run fine with the 1mm shorter plug.  I only had trouble running with a shorter plug on a .10 size motor, but it did run, although the idle was real bad. The head insert could be faced off 1mm, or a long reach plug used.  Is your plug burned out?  I don't know what brands of plugs are available over there.  Here we use K&B 1L, Fox long med. or hot likely.  Maybe a Rossi or Picco may be easier to get there.  Enya and OS are the medium reach though, so I would get a long unless the head is modified back to a medium reach.  It sounds like a dead plug to me though.  The gasket is really more of a shim for adjusting the compression ratio.  As long as it isn't damaged or torn it should be similar to the way it was.

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 6:34 PM   
CrashedTrainer


 

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Status: offline 		@aspeed: I removed the glow plug and put my finger on the the glow plug hole... by rotating the prop almost to TDC i could clearly feel the pressure on my finger tip... when i removed my finger air came out with pressure... i repeated this but this time i kept my finger on the hole for at least 5-7 seconds(clocked)... upon removing the finger slowly i could still feel pressurized air escaping from the the hole...
The glow plug is fine... checked it twice during the start up attempt... its an A3 type from OS...will check if any of the above glow plugs are available here..im sure i should be able to find at least one or two of them...

there is this one thing i feel which is out of the ordinary though... when i rotate the prop through the TDC with the glow plug removed, instead of feeling a slight/no restriction at the TDC it feels like the prop is passing through a notch internally... also i experienced the engine getting stuck at TDC when i was cranking it using the starter motor which previously never happened i.e. getting stuck at the TDC - the engine does eventually crank on if i do it by hand afterwards but again its a bit hard... i was thinking could it be because of bent piston pin or conrod deformation or bent crankshaft/conrod pin? it should be smooth through the TDC with a single restriction, right?

Thanks!

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 8:49 PM   
aspeed


 

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Status: offline 		No, that is normal.  Check to see if the compression leaks out with the plug tightened.  It sounds ok to me. As long as there is a glow in the plug, I see no reason for it not to go pretty much like it did before. The bump you are feeling on top is likely just the slop between the crankpin/rod and wristpin/piston combined with a good fitting pinch at top dead centre. I suppose it could be hitting the head with the piston, but that wasn't changed probably. Is it firing off of the prime?

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 9:15 PM   
CrashedTrainer


 

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Status: offline 		with the glow plug tightened i heard a very faint hiss of air leaking with the engine cranked to TDC.. i haven't done a soap test or something but im pretty sure that there is no air leakage from the glow plug or the head flange since on closer inspection the hissing sound appears to be coming from the carburator only and can be muffled when the carb inlet is covered with a finger..so i think the sound i hear is the air leak that is happening between the piston head and the cylinder which is not abnormal, right? again i could hear this faint leak for more than 10-12 seconds for each compression...
nope, its still the same original repaired head...how to make sure if the piston is hitting the head? i do hear only 2 or 3 fired strokes off of prime but that too after many attempts... i will give it another try tomorrow morning... will be looking forward to your reply for any more cues...

Thanks!

< Message edited by CrashedTrainer -- 12/7/2012 9:36 PM >

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RE: Stripped threads on OS 46AX Engine Head - 12/7/2012 10:38 PM   
aspeed


 

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Status: offline 		Sounds like the motor is ok anyway.  Just needs the usual starting procedures I think, strong glow, and enough fuel coming in etc. Don't put any water in it.  Maybe get someone over there to help you out, I am not sure how things work there, but an electric starter from a club member or something may help.

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