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May 22, 2019, 09:28 PM
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Discussion

saito valve seat repair


I have a saito 120 engine with broken valve seat. It leaks without compression. I would like to re-cut the seat. If any one has the experience of valve seat work, pls share your experience. Also, pls advise which tool I should to use.
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May 23, 2019, 05:19 AM
Registered User
I TOBOR's Avatar
Picture please, Thanks
May 23, 2019, 05:45 AM
Systems Test Engineer Amateur
Gary Cee's Avatar
Yep a picture would help a lot.
We were part owner and operated a cylinder head and automotive machine shop at one time so ,yes, been there

You say a broken seat; and that could mean a fairly deep cut that would render the cylinder a virtual scrapper. How did this damage occur?
In a full size engine, the old seat could be machined out and replaced with a fresh insert.
Cutting a new seat surface in a badly worn or damaged seat would sink or "pocket" the valve deeply , not a desirable condition. In some cases an oversized valve head is a remedy.

In the case of our toy engines, any major repair that one might consider would require an investment in tooling to some extent. Unless you are capable of that task yourself, the cost would be considerable.

Bottom line, probably cheaper/better to buy a new or good, used cylinder in the long run.

We will see what the pics and Dave have to say
May 23, 2019, 06:19 AM
Registered User
I TOBOR's Avatar
Dave may not know what to say, "broken seat" and "leaks without compression" are puzzling words.
May 23, 2019, 06:37 AM
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mike3976's Avatar
Most probable cause is overtight valve lash
May 23, 2019, 05:44 PM
Registered User
I don't think I've ever seen a "broken valve seat " before , in a model engine , either in the head or on the valve . Seen plenty that require a bit of TLC , but the pics will tell the story !!
May 23, 2019, 11:13 PM
Registered User
Thread OP
Quote:
Originally Posted by Gary Cee
Yep a picture would help a lot.
We were part owner and operated a cylinder head and automotive machine shop at one time so ,yes, been there

You say a broken seat; and that could mean a fairly deep cut that would render the cylinder a virtual scrapper. How did this damage occur?
In a full size engine, the old seat could be machined out and replaced with a fresh insert.
Cutting a new seat surface in a badly worn or damaged seat would sink or "pocket" the valve deeply , not a desirable condition. In some cases an oversized valve head is a remedy.

In the case of our toy engines, any major repair that one might consider would require an investment in tooling to some extent. Unless you are capable of that task yourself, the cost would be considerable.

Bottom line, probably cheaper/better to buy a new or good, used cylinder in the long run.

We will see what the pics and Dave have to say
The picture is here. I have already cleaned the valve and valve seat. However, it's still leaking as shown in the red dash line. If I put a good valve and still find the leaking. Vice versa, the E-valve put intake seat it looks seal good. I think it might be the E-valve seat did not have good surface and would like to cut a new surface. Thank you for all suggestion.
Last edited by sqhnsd; May 23, 2019 at 11:24 PM.
May 24, 2019, 02:20 AM
Registered User
It is not so awful clear, but the valve guide looks odd... has it moved? The pic looks like the guide (inner bronze part) is in another insert....they do not look concentric to each other...
May 24, 2019, 05:33 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Anyone notice the glow plug element is a little frosty looking and pushed off to one side of the plug body? The valve seat looks chipped too. Like a chunk cracked and broke off.

<g>
Last edited by 1QwkSport2.5r; May 24, 2019 at 07:22 AM.
May 24, 2019, 06:09 AM
Registered User
I TOBOR's Avatar
The valve guide is bent inward as if the outer edge of the valve was struck by the piston. There appears to be a piece of the valve spring broken off and stuck in the valve spring groove.
May 24, 2019, 06:18 AM
Systems Test Engineer Amateur
Gary Cee's Avatar
Quote:
Originally Posted by sqhnsd
The picture is here. I have already cleaned the valve and valve seat. However, it's still leaking as shown in the red dash line. If I put a good valve and still find the leaking. Vice versa, the E-valve put intake seat it looks seal good. I think it might be the E-valve seat did not have good surface and would like to cut a new surface. Thank you for all suggestion.
I must have missed the referenced pic of the "valve spring groove". The valve spring seat would be topside, not underside.
Anyhow, if you want to send the cylinder, I can likely repair that valve guide or replace it for you . Only cost would be shipping.
May 24, 2019, 06:24 AM
Registered User
I TOBOR's Avatar
Good catch, I was so intent on looking at the guide I didn't pay enough attention the surrounding area.
May 24, 2019, 06:27 AM
Systems Test Engineer Amateur
Gary Cee's Avatar
Thanks Dave,
I was thinking a pic had been removed before I had a chance to see it

Could be an easy fix.

BTW , The one piece cylinder and head is one of my favorite features with Saito Engines.
May 24, 2019, 06:40 AM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Edited out the crud.
Last edited by 1QwkSport2.5r; May 24, 2019 at 07:23 AM.
May 24, 2019, 06:52 AM
Engine man
dmrcflyr2's Avatar
That just leaves more Saito and OS engines for the rest of us then! It is truly unfortunate that the appearance of an engine keeps one from experiencing one the finest 4 stroke engines made. I guess you have to experience some things to appreciate them.


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