labernyth seal ?

[X-Wrench]

i am helping a freind with his merc 4 cylinder 40 hp mercury. initialy, it blew apart a reed block, and of course, it ran very poorly. he bought a used part, and it still runs very poorly. this is where i came into the picture. he has it all apart, and the used reed block, while it looks good, has what i feel is a horendous amount of clearance on the crankshaft. and, the i.d. is oblong to boot. there is between .018" and .026" of clearance between the crank and the seal. the crank looks fine, with no markings other than the factory machining. and of course, the seal is widest along where the seal splits, so lapping the seal would only make it more out of round. he has a computer manual, i do not know who makes it, but we can not find any specs for this. first, i would think that the seal should be round, and second, the clearance seems to me like it is way to much. a bit about myself, i am a former motorcycle mechanic, so while i have a lot of experience on motors, i am not real familiar with reed valve motors. also, this runs poorly over 1/2 throttle (which is basicly about when the throttle plates open). would this (excessive valve clearance) account for this condition? or is it more likely a problem with the carbs/ fuel pump (which i am thinking is more likely)?

 

[emckelvy]

Re: labernyth seal ?

Worn reed block labyrinth seals can be a cause of hard starting and poor idling. Not so much so a problem at higher rpm. So maybe you've got other issues besides, like ign or fuel delivery.

But the wear you describe in the reed block does seem excessive. And the hole definitely is supposed to be Round not oblong!

You can also tell wear by checking the grooves of the labyrinth seal, they should not be mushroomed where they interface with the crankshaft. The width of the grooves should be consistent all the way thru.

You should be able to compare that part to the other reed block on the crank. You can tell a lot by how much the reed block "wobbles" on the crank.

You may be able to pick up a good used reed block on eBay, that would be a common part to be sold out of a dismantled motor. They're pretty $$$pendy new, if even available still.

At any rate, it'd certainly be worthwhile to track down a good reed block, it should improve idle quality if anything else.

Far as the running issue, I'd go thru the carbs and rebuild fuel pump(s) then take it from there.

HTH............ed