Roby

I have an OS 120 E with a exhaust valve that just won’t stop leaking no matter
what I do. I’ve gently lapped the valve several times but to no avail. Finally I decided
to just get a new head only to find out that they’ve been discontinued. (isn’t that nice)

Anybody have any suggestions on how to fix up the head or am I now the proud owner
of a “parts only” engine.

Regards,
Roby

Bax

My Feedback: (11)

If the valve leaks when you turn the engine over by hand, it's normal. The rapid movement of the piston when the engine's running adds force to hold the valve closed. If it's leaking when the engine's running, and lapping doesn't help, then you likely need a new cylinder head and valves.

Konrad

What gives you the idea that you have a problem? Have you noticed a performance drop (poor idling and/or loss of top end power)? What do you mean by "gently lapped the valve "?
Most wear out of the four cycle engine heads (toy and full size) can be traced to the valve guide. If the valve guide is worn out no amount of "lapping" will fix the seal.

If you know a real good machinist the guide can be replaced. I have done this on the Enya 1.20R. This is often a benefit of belonging to a large club. Somebody there might own a machine shop and as a benefit to the club members offer to help with some part fabrication. Barring the ability to replace the valve guide it is a parts engine

Friends don't let friends fly nickel,

Konrad

Roby

Bax and Konrad.

Thank you for your replies. Although the motor runs fine at idle and has enough power
to pull up a Fly-baby, I suspect that it's not going to run well enough much longer.
At one time I used to flip start this motor . Now the compression is so low it won't start
without a electric starter.

When I lapp any valves , (auto,marine,or small engine ) I always make sure the seal is liquid
tight. On this OS the intake is perfect but the exhaust weeps .

Bax, where can I get a new head for this motor ? The part number is 45504111 or
45504021

Thanks,
Roby

Campgems

Roby, dont equate these engines with car and boat 4 strokes, they are completely different animals. Valves leak on these engines. You may try a fresh set of springs. Or as suggested new valve guides. I don't remember if the guide and seat are one piece on this engine, but that is another option.

Iknow your frustration on a replacement head being discontinued on an eng\ine that is currently being sold by Tower. I found this out about 6 months back when I found a Surpall II engine I bought on Ebay had a stripped glow plug hole and a broken boss that the rocker cover screwed into.It uses the same head. Imanaged to salvage the head by sending it to Clarence Lee for heli coils for the glow plug, and a little creative machining on my own to get a set of threads that would let me screw down the rocker cover.

The trouble with using that engine for a parts engine is that a lot of the parts on the 120's seem to change between series. There is a slight difference in crank cases between tthe E and the three Surpass models. Manifolds, pumps, regulators carbs are all different. I think the prop nut is interchangable between engines though

Don

Konrad

No, OS did not make this head or any other head with user replaceable valve guides. These need to machined out to allow for a thin wall replacement guild to be pressed fitted in place (0,005 mm). This is a rather tricky proposition. And not really recommended unless the machinist is willing to do it just for the love of engines. You don't want to pay what his/her time is worth!


Friends don't let friends fly nickel,

Konrad

Broken Wings

My Feedback: (20)

What model engine manufacturer does?.........(user replaceable valve guides......)

Konrad

Don't know, you tell me. Sounds like you might be a little defencive about what OS offers the consumer for the price they charge. [:'(] If you have an issue with that please take it offline!

All I state is that OS four cycle heads do not have user replacable valve guides. Please don't read anything more into that statement!

Now there might be something hidden in the sign off.

Friends don't let friends fly nickel,

Konrad

Campgems

Konrad, I didn't reference a user replaceable valve guides, just a unitized valve guide/seat. Also, where did you get the 0.005mm from. That number is so small that no machine shop could machine a wall thickness that thin. You are talking gold leaf thin. Less than 0.0002"

Numbers aside, a good hobbyist machinist could make a bronze bushing valve guide, or for that mater, a unitized guide/seat. I'm not all that sure it would be any better though. The valve seats on the 1.20 head are really close to the glow plug threads. Any pressing in of a valve guide could easily distort the threads, the fit is that close. A better solution if the design allows it is a wiper on the valve, but again, I'm not sure it would gain you that much.

When you are talking spring pressures as low as you find in this engine, you need a razor sharp seat. Lapping the valve/seat will probably increase the seat band by a factor of five or 10 and reduce the effective seal by a considerable amount. When you consider that the valve spring only has four or five pounds of closing pressure on the valve and the valve is roughly 3/8" diameter. with a sharp seat edge on the valve, things are OK, but when you take the 0.001" wide seat to 0.010" that spring pressure isn't near enough to form a good seal. My recommendation is to not lap the valves at all.The probability is great that your are going to do more harm than good.

Don

Konrad

BW,
??? I thought the subject was the OS head with a leaky exhaust valve????

No, I don't know of any manufacture of our toy engines that offers user replaceable valve guides. But then there are a lot of manufactured that I know little or nothing about. I wonder if Technopower, Kalt or even Kavan had this feature.

Do you know of any OS or for that fact another manufactures head that has user replaceable valve guides? It might be a good idea at the price some manufactures are asking for their four cycle engines.

Your point in asking this about other manufacture is?



Friends don't let friends fly nickel,


Konrad

Konrad

Don,
The 0,005 mm is what I used as a press fit along with high heat bearing locking Loctite compound. As for the wall thickness of the replacement guide I fashioned it so that it was about 40% of the material cross section of the original guide of the Enya 1.20R

I agree about lapping of valve seats. I did look at a valve set for a Saito 120/150 and noticed a rather interesting valve seat. Don't know how this would pertain to the OS

I'll look for my file on this and post it

All the best

Konrad

Here is what I found about the valve seat profile of the Saito 1.20 It supports your statement about the rather narrow valve seat. Can't say as I have seen a sharp valve seat in any engine over 15 cc.

I was looking at this valve seat in regards to chrome plating so it doesn't fully apply to the valve guide / valve seat issue here.

The report starts here:
Here is a crude drawing of what I saw under the SEM. Please note I’m not a metallurgist nor did I do an extensive study. When I looked at the 2 heads in the SEM all I wanted to learn was; is there plating in the large bore Saito valve seat, there isn’t. I did not take any digital photos nor did I save (write) any of the spectrum plots. As I didn’t want any records that could be traced to this project.

The conclusion is that there is no chrome plating in the valve seat. The spectrum did show chrome, but the SEM operator said it was to be expected as it was noise (electron bounce) from having to look down inside the chrome cylinder bore. He did show me some microscopic particles imbedded in the seat that came from the cylinder wear (neat stuff).

The angles are approximations as I did not do any cross sectioning of the head.

The aluminum grain structure is horrible as there are a lot of oxides and voids in the matrix. Again I’m no metallurgist this is from what the SEM operator was telling and showing me.

Just to be clear it would be very difficult to plate the valve seat, as one would need to have a very accurate masking process for both the zinc strike and chrome plating process. Also as chrome does not lie down evenly the seat would need to be ground to finish size.
I can tell you that looking at the tool marks the valve seat is cut by a shaped cutter not a grinding wheel.
One last point if the Saito did chrome the valve seat I’m sure they would advertise it, as it would be a hell of an achievement.
I would have to say I see no benefit to a chrome seat as I would think it prone the thermal shock and would dis-bond in a hurry. Also the plating would impede thermal transfer from the valve to the head.
Again the heads I looked at, a used big head Saito 120 and a new Saito 150 do NOT have chrome plating in the valve seat. The seat is cut directly into the aluminum head with a shaped cutter.

Please note the very small raised seat (aproximatly 0.006 x 0.040””) any attempt to lap the seat will most likely remove this feature. Loss of this feature will result in less flow across the valve seat at low valve lifts. I strongly recommend one do NOT lap the seat to the valve.

weluvengines

OS DID make engines that could have the seat and valve guide pressed out of and back into the engine. Here is a picture of an OS FS90 head along with the complete valve mechanism from a 90. All the original OS 4 cycles including the 60, 75, 80, 90, and 120 plus the twins used this method. I pressed this one out using a drill press as the guide was bent. I pressed in one from a destroyed engine using the drill press and it worked perfectly. I think Enya did the same thing.

Broken Wings

My Feedback: (20)

It was just a question, now I know the correct answer.

Thanks

Konrad

Yes, I knew that the valve pocket, valve guide and valve seat were pressed in bronze inserts. What I don't know is if the thin walled valve seat will maintain its shape and concentricity after it has been reinstalled. I though that the valve pocket, valve guide, and valve seat were machined into the insert after it was installed in the head to ensure that these feature are accurate and not distorted. I don't think OS intended these to be user replaceable, just for the above mentioned concerns.

Glad to hear you had success with the insert change out.


Friends don't let friends fly nickel,

Konrad

Konrad

Care to share that with us?

Friends don't let friends fly nickel,

Konrad

Roby

Thanks to everyone for the replies. Since a replacement head is no longer available, I can't
get the valve to seal, the compression is way down as a result, it looks like I now have a
parts only motor. WHAT A WASTE !

I sure hope this sort of thing doesn't happen with my multi cylinder units. I'd hate to shelve one of those
because I couldn't get a replacement part.



Regards,
Roby

Luna_Rendezvous

nothing lasts forever, use and enjoy them while you can

earlwb

I would use some patience and start looking for another used engine. It might have a good head but something else wrong with it.

Bax

My Feedback: (11)

The replacement cylinder head can be special-ordered through us:

OSMG5138 45504110 CYLINDER HEAD 120SUR US$84.99
OSMG5235 45504020 CYL HD & VALVE 120SUR US$164.99

Allow about 6 weeks for delivery from Japan.

Konrad

Roby,
The OS customer support rep can’t condone this, as it is not part of OS’s policies.

But at that price and lead-time it looks like the machine shop is a viable option. Ether a thin walled guide replacement like I did. Or a full bronze insert replacement with port cut in after installation (recommend this option).

Here in Silicon Valley one can find machine shops that are equipped to do this kind of small delicate work. They are euphemistically called engineering firms. One needs to look very close to see it the firm can move metal or if they are in fact strictly an engineering firm that pushes only paper, when one looks for them on the web of in the yellow pages. With the economy like it is you stand a good shoot at finding a shop that will do this but you will most likely need to do visit them in person.


Friends don't let friends fly nickel,

Konrad

Roby

Thanks BAX .
Chances are I'll pop for the new head.

Regards,
Roby

Broken Wings

My Feedback: (20)

$84.95 for a new cylinder head.... It will cost you that much to walk in the door of an "Engineering Firm" or a machine shop. Have them make mutiple set-ups to machine the parts install them and re-cut the port(s) in the cylinder head.....

Thanks Bax. It's good to know you can buy O.S. Parts that are no longer carried at Tower.

Konrad

If the shop is busy with say, some government work I'd agree. But if the shop has a lot of down time (as a result of the poor economy) it is an option. Ok, the $85 dollars is pushing it I was looking at the $165 price tag. But a 6 week lead-time looks like that would lay up this engine until next year's flying season. Like I said earlier, one really wouldn't want to pay what the machinist's time is really worth.

Friends don't let friends fly nickel,

Konrad

weluvengines

Amazing. In this forum konrad is from San Francisco and in his posts on RCgroups he is in Everett, Washington. He posted on RCG for a couple years in Everett until he was banned last week. He said he was some kind of engineer in Everett. He hadn't posted on RCU in a couple years. He gets kicked off of RCG last week in Everett and suddenly shows up here again on RCU in San Francisco. How is it he can move around so fast? It is getting very hard to believe much of anything he says anymore.


As the WHO sang in their famous song, "Who Are You, Who, Who?"

By the way San Francisco is not considered in the "Silicon Valley" which is the Santa Clara Valley. Mostly in the Mountain View, Sunnyvale and San Jose area.

w8ye

My Feedback: (16)

He''s still in Everett