Hello, have a 77 340 exciter and had the cylinders bored 1st over. Put it back together and had 90 lbs on the pto side with 100 on the mag side. Is there a center seal in the crankcase of these that would cause the lower comp? Thanks Rich.
opsled
Active member
Yes there is a center seal which could be an issue. Did you do anything with the lower end?
What head gaskets are you using??
Could be your culprit. Originally the were thin metal gaskets. The replacement even from Yamaha is a much thicker fiber type. The replacement is the same gasket as the Enticer 340 used.
If that is what you are using that is probably the problem.
10lb difference between sides is an issue too but that also could be gaskets. Should be closer than that.
opsled
What head gaskets are you using??
Could be your culprit. Originally the were thin metal gaskets. The replacement even from Yamaha is a much thicker fiber type. The replacement is the same gasket as the Enticer 340 used.
If that is what you are using that is probably the problem.
10lb difference between sides is an issue too but that also could be gaskets. Should be closer than that.
opsled
Hello. i used the fiber head gaskets. I have a used set of the thin metal ones. Could they be reused? Thanks Rich.
Just went and chaged out the head gaskets and comp. is now 100 on pto 110 on mag. I have not done anything to the bottom end yet. Thanks.
opsled
Active member
The metal head gaskets can be reused. Most like to give them a coat of spray on Copper Coat or an equivellent.
That reading is still low. What you are using for a comp tester could play into it. A good tester that is known to be acurate and has a long reach screw in adapter is the best and will give a true reading. Each cylinder should pump it's max in no more than 3 pulls of the rope.
A good engine should be around 120ish. It should come up a bit once the rings seat so the 110 # is probably OK. The 100 # bothers me. They should be almost equal. If they were both at 110 I'd say OK.
What did you use for base gaskets? There may have been differences in thickness on them over the years aswell. It they were different that would also cause issues.
I have a simple leak test for crank and center seals that I use when the cylinders are off that works well. Just fill one crankcase cavity with fuel to a level above the top of the seals and slowly rotate the crank. If the center seal is out fuel will show up in the other cavityand if an end seal is out it will leak there. If there are no leaks empty that cavity, blow it out dry and repeat on the other side. If there are still no leaks your seals are good.
Good Luck, opsled
That reading is still low. What you are using for a comp tester could play into it. A good tester that is known to be acurate and has a long reach screw in adapter is the best and will give a true reading. Each cylinder should pump it's max in no more than 3 pulls of the rope.
A good engine should be around 120ish. It should come up a bit once the rings seat so the 110 # is probably OK. The 100 # bothers me. They should be almost equal. If they were both at 110 I'd say OK.
What did you use for base gaskets? There may have been differences in thickness on them over the years aswell. It they were different that would also cause issues.
I have a simple leak test for crank and center seals that I use when the cylinders are off that works well. Just fill one crankcase cavity with fuel to a level above the top of the seals and slowly rotate the crank. If the center seal is out fuel will show up in the other cavityand if an end seal is out it will leak there. If there are no leaks empty that cavity, blow it out dry and repeat on the other side. If there are still no leaks your seals are good.
Good Luck, opsled
Hello, thanks for the tips. I used yamaha base gaskets but did not measure them. i will try the gas trick tomorrow. Thanks Rich.
opsled
Active member
One thing I forgot to say about that test is to oil the bearings afterwords if everything checks out OK. The mains can be fed oil through the holes in the upper case that are below the transfer ports in the cylinder. Squirt some oil in the holes and rotate the crank. Rods are evident. Oil can or small squezze bottle with 2 stroke oil will work.
opsled
opsled
dynofun
New member
- Joined
- Nov 14, 2005
- Messages
- 355
Whoa... None of that applies to this sled op. The center seal is a labrynth and will let gas through like it isn't there. It is very unlikely that your low compression is due to the center seal. That comp is very low. Stock that motor should be 130# or so depending on gauge...
opsled
Active member
dynofun said:
Don't know what to tell ya.
Just parted a near perfect 77 EX340 engine last month. It didn't leak across. The crank was perfect. Sold for $197. Guy was happy as hell with it.
http://www.ebay.com/itm/190647165005?ssPageName=STRK:MESOX:IT&_trksid=p3984.m1587.l2649
That went so well I tore down two extra EX 440 engines I had to part out.
Both leaked across the center and both cranks were junk. Mains were loose and slid on the shaft with ease. One had a crack in it and cases were rattled.
This method has always worked for me. Been doin it for years.
What is your method for testing center seals???
I'm always willing to learn something new.
opsled
Hello, opsled, i think im the one that bought your cyls,pistons for extas. Got them from ebay. Thanks for the help.
dynofun
New member
- Joined
- Nov 14, 2005
- Messages
- 355
opsled said:
Sorry opsled, haven't been on here in a while. If you had a NEW crank with a NEW seal and it had thick oil on it, gas would not flow to the other side as if it isn't there like I said above. It would still be pretty fast though so I don't know what to tell you. The labrynth seal makes no contact to the crank to provide "the seal". In fact, it is a pretty big gap. It only works by being a "labrynth". The air fuel mixture can't cross over fast so it creats a buffer and works just fine.