Honda Spree and Elite 50 Forums

I have a low compression (30lbs) scoot. Piston, rings and cylinder all look good so I moved on. I sealed the exhaust, the intake manifold and delivered air through the spark plug hole. The only leak I found so far is from the reed valve assembly. 5-7 lbs. of air into the crankcase and air flows constantly from the reeds. Further inspection shows 4 reed petals, 3 of which are open. One is open .008" and two are maybe .004". These are plastic petals which, according to the wiki, typically can be partially open. However, I would have expected my crankcase pressure to have closed them. Any comments on the reeds?

Flip them around, or find replacements.

i got some

eclark5483 wrote:Flip them around, or find replacements.

I flipped one side. Still not sealed.

jakubman1 wrote:i got some

New? Size?

Even though they're open at rest, should these things not close with crankcase test pressure? This is my first time looking at and trying to understand reeds.

i found 1 on ebay :

https://www.ebay.com/i/332461234112?chn=ps

jakubman1 wrote:i found 1 on ebay :

https://www.ebay.com/i/332461234112?chn=ps

Good find. Don't know what year he has but those are 86-87 model year reeds, AKA SB50 reeds. Would be an absolute improvement to stock reeds if he has an 84-85.

The only thing questionable that I can see is this area right here.



Is that a chip? Or maybe just some residue? Who knows? Either way, that is exactly what he should be looking for. But then again, he said:

inspection shows 4 reed petals, 3 of which are open.

4? What kind of bike is this? Obviously not a Spree.

mikehailwood wrote:Even though they're open at rest, should these things not close with crankcase test pressure? This is my first time looking at and trying to understand reeds.

Open at rest? They should be closed at rest and only open during the piston's down stroke when vacuum is created. When you pressurize the engine block, the reeds should seal and be closed to prevent air from escaping, thus, increasing compression..

mikehailwood wrote:I have a low compression (30lbs) scoot.

This condition is not reed related....period

eclark5483 wrote:

mikehailwood wrote:Even though they're open at rest, should these things not close with crankcase test pressure? This is my first time looking at and trying to understand reeds.

Open at rest? They should be closed at rest and only open during the piston's down stroke when vacuum is created. When you pressurize the engine block, the reeds should seal and be closed to prevent air from escaping, thus, increasing compression..

As I mentioned earlier, they are just slightly open at rest but leak when the crankcase is pressurized. This does not seem right. So while the reed condition may not be contributing significantly to any compression issue, should the reeds be replaced?

Meatball wrote:

mikehailwood wrote:I have a low compression (30lbs) scoot.

This condition is not reed related....period

Good to know. As I mentioned in my first post, cylinder, piston and rings all look and measure good. Pressurinzing the crankcase, the first and most obvious leak was the reeds. So I thought I'd address that as long as I have them removed. Then I'll continue searching for leaks. Can anything besides the top-end components cause such a low compression reading?

Blown head gasket will cause low compression. As meatball said the reeds have absolutely nothing to do with the compression reading.

mikehailwood wrote: Can anything besides the top-end components cause such a low compression reading?

Reeds do not raise or lower compression. You can REMOVE the reeds and still have compression!!

Low compression would be top-end related. Worn cylinder/rings, pressure escaping from head gasket or spark plug, damaged/cracked/melted piston crown, cracked head...etc etc.

Greetings:

I'll take the opposite position; Leaking reed valves CAN reduce compression readings at the gauge. So can doing the compression test with a carb installed and the throttle closed. So can leaky crank seals. But your values are SO low (30psi?) that there's almost certainly a bad ring/cylinder seal despite looking OK.