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May 24, 2019, 08:15 PM
Need more speed!
Chuppster's Avatar
Thread OP
Help!

Leaky Valves - Need more compression!


I have a friend that just bought a second had Saito Fat Head 120, and it has very little compression. When we first got it the valves were stuck. We pulled the head off and removed the intake valve (the more stuck one) and gently cleaned it up with a plastic scratch pad. Now both valves move freely but they do not seal. Is there a way to get them to seal again?
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May 24, 2019, 08:24 PM
Systems Test Engineer Amateur
Gary Cee's Avatar
Set the valves, run the engine.

After a few tanks you can re-evaluate.

Then check for leakage points and sources.
May 24, 2019, 09:01 PM
Need more speed!
Chuppster's Avatar
Thread OP
Quote:
Originally Posted by Gary Cee
Set the valves, run the engine.

After a few tanks you can re-evaluate.

Then check for leakage points and sources.
How can I run the engine if there is almost no compression?
May 25, 2019, 05:57 AM
Registered User
I TOBOR's Avatar
Chupp, a trick that sometimes works, push the valves open about 1/16" with your finger nail and then let it snap shut, amazing what that will do for leaky valve. If it works you'll need to readjust them.
May 25, 2019, 06:13 AM
Systems Test Engineer Amateur
Gary Cee's Avatar
Like I TOBOR said, and perhaps add some oil or fuel around the valves. Push on the stems only . If you push on the edge of the spring or retainer you run a risk of losing a valve keeper.

Still, they often start without all that by just the starting operation. A bit balky perhaps but the fuel priming wets the engine and flipping the prop will often free up the valves.
May 25, 2019, 09:38 PM
Registered User
kimchiyuk's Avatar
Quote:
Originally Posted by Chuppster
How can I run the engine if there is almost no compression?
Doesn't need much compression to run; much less than you'd think! Sometimes after rebuilding an engine one or both of the valves will sound like they are leaking. You won't have that nice snappy compression we always look for. Once they run a bit, the compression comes right back.
May 26, 2019, 06:20 AM
Need more speed!
Chuppster's Avatar
Thread OP
Quote:
Originally Posted by kimchiyuk
Doesn't need much compression to run; much less than you'd think! Sometimes after rebuilding an engine one or both of the valves will sound like they are leaking. You won't have that nice snappy compression we always look for. Once they run a bit, the compression comes right back.
We ran it yesterday an I was surprised that it fired! We tinkered with it but I have yet to get it to idle. It appears that the exhaust valve is still not seating properly, so I guess we will give it a tank at full throttle and see how that goes.
May 26, 2019, 07:37 AM
Systems Test Engineer Amateur
Gary Cee's Avatar
Check the rocker clearance . It may have closed up and could prevent the valve from fully seating.
May 26, 2019, 07:47 AM
Club Saito | Genesis 8:11
Bunnyshooter223's Avatar

Valve Leakage, me too


Quote:
Originally Posted by Chuppster
We ran it yesterday an I was surprised that it fired! We tinkered with it but I have yet to get it to idle. It appears that the exhaust valve is still not seating properly, so I guess we will give it a tank at full throttle and see how that goes.
Same issue here, but intake valve seal on an FA-50.
New valves, it's the head side. A new glow plug seemed to help a lot, but it would not idle low without dying. Difficult to start when warm. Compression feels low, comes up a bit when primed but low overall. Sometimes erratic power at mid-throttle

The head on mine is 'kinda rare' too as it is a 'newer FA-56 style'

Edit: mine had original valves strike piston, don't know why. I just wanted to share my symptoms because it seemed to run well enough, at first, that i posted it for sale. But i quickly pulled it after testing it more
Last edited by Bunnyshooter223; May 26, 2019 at 09:10 AM.
May 26, 2019, 08:07 AM
Registered User
Cougar429's Avatar
From your description it sounds like things were stuck from long term storage.

Did you remove the exhaust valve completely to clean? That would have allowed you to also see if damage to the valve or seat surfaces.

Are the seats plated or bronze?

How was the compression once the engine was hot?
May 26, 2019, 09:16 AM
Systems Test Engineer Amateur
Gary Cee's Avatar
The compression was originally nil but came up after the initial running. That is why the valve lash should be re-checked. If the compression improved there is an excellent chance that the valve lash closed up.

No plated seats.
May 26, 2019, 11:50 PM
Diesel Danny
danny mz's Avatar
It might be worthwhile checking the rings too.

I have encountered a few old engines where the rings were stuck in the grooves with resulting low compression.

* Danny M *


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