testing reeds

[evilone]

Is there a way to test the reeds other than by looking at them?

[CharlotteSpreeRider]

Leak test. There was a thread a few weeks ago with a link to a dude demonstrating how it's done on You Tube.

[evilone]

Do you remember if it was the pressure or vacuum test?

[CharlotteSpreeRider]

Well, you really should do both. But, pressure is probably easier to test, and I'd think reeds would fail subtly more on the pressure than the vacuum. If they failed on the vacuum, the motor probably would not run at all.

[trains420]

if you have a compression tester, and you got low psi, mine has a little thing with it, and it says, to check if it's rings, or cylinder, or the reeds. it can also be the head gasket. i guess, soap could check that. if you have low psi, take out the tester, and put a tablespoon of oil in the spark plug hole. you'll get higher psi if it's rings or cylinder, if not, then reeds. or valves.
i don't know what it says about head gasket.

[mousewheels]

A seat of the pants check I do is pull the plug, and rotate the crank by hand. You should hear a 'thwop' and feel a pulse of air when the intake ports open. If the reeds are broken - nothing will be felt. If leaky, you may hear the air flow out the reeds.

This test has caught a worn reed block and an engine with bad seals. Not the best of tests, but something which requires no equipment.

[Bear45-70]

Only pressure can test the reeds. Vacuum pulls the reeds opens. FYI, it is not imperative that the reeds be totally closed when the engine is not running, as long as when the crankcase pressurizes the reeds close and seal (well sort of seal). You guys are aware that by the time you hit 1/2 to 3/4 throttle the the reeds never close, there just isn't time for them to actually close. The reeds are for low speed and midrange operation only. We had some racers in the non restricted 66 CID outboard class that mounted another carb on the intake cover on the transfer port with no reeds and no idle circuit. Once the engine reached WOT on the regular 3 carbs, they hit a solenoid that open the second set of 6 carbs (one on each of the 6 intake cover, to WOT also. The reed cages on these engines are very restrictive by design so this solved that issue. They got about 1800 to 2000 more RPM over the 6600 the stock reeds allowed.

[trains420]

when the engine starts to compress, if the rings have leaks then you'd have less compression. with a compression tester, you can get your compression, then if it's low, some oil could seal leaky rings. and then if your compression didn't change, then it's your reeds.
this could work, just a suggestion. it came with my compression tester. not saying it's wrong. not saying it's right either. it said it though.

[bakaracer]

when the engine starts to compress, if the rings have leaks then you'd have less compression. with a compression tester, you can get your compression, then if it's low, some oil could seal leaky rings. and then if your compression didn't change, then it's your reeds.
this could work, just a suggestion. it came with my compression tester. not saying it's wrong. not saying it's right either. it said it though.

When doing a cylinder compresion test,the reeds don't come into play.the tester is only reading compresion from the exhaust port up so only the rings and piston come into play.when doing a case pressure test,now thats when the reeds will affect that.Don't get the 2 mixed up.theres cylinder compression and case compression. 2 different things.

[Wheelman-111]

Greetings:

A rare occasion when I disagree with The Distinguished Bakaracer. I believe the reeds do affect compression readings, a little. If they aren't airtight, the case charge blows back before the posts close and you get a little lower reading than if they're tight.

Most service manuals also prescribe that if a carb is mounted, you must also open the throttle all the way to obtain an accurate reading. What happens otherwise is that the case inhales a breath under negative pressure, once again producing a lower-than-true result.

With all that said, the results probably don't change more than 10 or 15 percent, if that.

[bakaracer]

Greetings:

A rare occasion when I disagree with The Distinguished Bakaracer. I believe the reeds do affect compression readings, a little. If they aren't airtight, the case charge blows back before the posts close and you get a little lower reading than if they're tight.

Most service manuals also prescribe that if a carb is mounted, you must also open the throttle all the way to obtain an accurate reading. What happens otherwise is that the case inhales a breath under negative pressure, once again producing a lower-than-true result.

With all that said, the results probably don't change more than 10 or 15 percent, if that.

Are you Sure? the exhaust port is higher than the transfers so air is blowing out threw the exhaust as the piston goes up.after the exhaust port is where the cylinder compression read is.plus if anything more than around 9psi,the reeds will blow out and shread to pieces.case pressure gets up to around 6 psi in these little engines.The manuel tell you to hold the throttle open so airflow coming into the engine is not restricted .

[bakaracer]

Hey but I will take the intake and reeds and do a compression test with and without it and see what it tells me.