Quad comprestion check
#1
03-09-07, 10:59 AM
Quad comprestion check
The other day i did a comprestion check on my dads quad. It is a Yamaha Moto 4 200 1986. My dad owns two of the same quads. Last summer we had the quad rebuilt and bored 20 over. It has been about six months now since then.
In the owners manual It said For Stock rating was:the minimum 114, maximum 142, Standard 128 lbs. I under stand that since it has been bored 20 over that it will have more comprestion. But what do you do with a quad that has 185 lbs.
First one is my blue one it has/or pushing 165 lbs. The second one is my dads red quad that one is pushing 185 lbs. the starter can not turn the engine over fast enough.
On the right side of the jug i can see oil there. i think it is leaking b/c of amount of compression.
what else could go wrong.
I am probably not going to do any thing to this quad exept buy new cluches for the red one and put them on in the summer.
please tell what you think about this.
In the owners manual It said For Stock rating was:the minimum 114, maximum 142, Standard 128 lbs. I under stand that since it has been bored 20 over that it will have more comprestion. But what do you do with a quad that has 185 lbs.
First one is my blue one it has/or pushing 165 lbs. The second one is my dads red quad that one is pushing 185 lbs. the starter can not turn the engine over fast enough.
On the right side of the jug i can see oil there. i think it is leaking b/c of amount of compression.
what else could go wrong.
I am probably not going to do any thing to this quad exept buy new cluches for the red one and put them on in the summer.
please tell what you think about this.
#2
03-09-07, 02:54 PM
The .020 over bore in itself shouldn't significantly affect the compression. The difference lies in the compression cavity in the head remaining the same while you have enlarged the bore. The extra bore volume would be pushed into the unchanged head configuration, so you would see a little more compression.
Since you're getting outside the bounds of the specs, though, I would look for a reason. First try a different compression tester. You would feel badly if you went to a lot work correcting something that was no more than the tester's fault. If that's OK, I would make sure the piston bore is clear of all oil before checking. Run the engine and let it cool. As soon as it's cooled down, check it.
If you are still getting the 185 with the max spec being 142, the problem would likely be a tight bore for the piston you have or the ring gap. If the engine hasn't been ran a lot, it may loosen up as everything seats in and the microgrooves straighten out. If after you've given it a breakin period and the high compression is causing problems, you may have to dismantle the engine to have the bore checked and corrected along with the ring gap.
A problem resulting from overly high compression would be pinging or preignition. Because of the potential damage involved, it would pay to get it taken care of.
Hope this helps,
Bob
Since you're getting outside the bounds of the specs, though, I would look for a reason. First try a different compression tester. You would feel badly if you went to a lot work correcting something that was no more than the tester's fault. If that's OK, I would make sure the piston bore is clear of all oil before checking. Run the engine and let it cool. As soon as it's cooled down, check it.
If you are still getting the 185 with the max spec being 142, the problem would likely be a tight bore for the piston you have or the ring gap. If the engine hasn't been ran a lot, it may loosen up as everything seats in and the microgrooves straighten out. If after you've given it a breakin period and the high compression is causing problems, you may have to dismantle the engine to have the bore checked and corrected along with the ring gap.
A problem resulting from overly high compression would be pinging or preignition. Because of the potential damage involved, it would pay to get it taken care of.
Hope this helps,
Bob
#3
03-09-07, 04:28 PM
The compression tester i used was from my teacher b/c the one i have is juck and old. The head in new but the same size as the original.
I also forgot to mention was that: the guy we bought the quad from, bought the quad in parts. all the parts were setting outside. he put the quad to gether. as we were rebuild the quad i saw the the crake looked a little rusty but not bad. could this cause any thing. i personly don't think so, but i would like you apinion.
its been about 9 months since its been rebuilt i changed the oil after the break in.
could you explane this
I also forgot to mention was that: the guy we bought the quad from, bought the quad in parts. all the parts were setting outside. he put the quad to gether. as we were rebuild the quad i saw the the crake looked a little rusty but not bad. could this cause any thing. i personly don't think so, but i would like you apinion.
its been about 9 months since its been rebuilt i changed the oil after the break in.
Originally Posted by marbobj
A problem resulting from overly high compression would be pinging or preignition. Because of the potential damage involved, it would pay to get it taken care of.
Bob
Bob
could you explane this
#4
03-09-07, 07:52 PM
The rust on the crank would depend on where it's at. If it's on the rod bearing or main bearing journals, it would have to be cleaned and the crank journal polished. Otherwise the rod or main bearing would wear prematurely. Rust anywhere else on the crank could be cleaned off with steel wool.
In terms of the preignition/pinging:
In an engine the piston travels up on compression. Before it reaches top dead center (TDC) the spark ignites the fuel/air. When the spark occurs is controlled by your setting for the ignition timing. Before the piston reaches TDC a certain amount of expansion of the fuel/air occurs adding to the compression inside the combustion chamber. If the ignition is set too far advanced or if the compression which you're measuring is too high, the pressures inside the chamber get too high and a dieseling effect occurs before the piston can start back down and the valves open to relieve the pressure in the combustion chamber.
Instead of a slow burn across the combustion chamber from a single flame front originating at the spark plug, you have two fronts. One from the spark plug and another from the dieseling effect. When the two fronts collide you have a ping which essentially rattles the metal parts (valves and piston, etc.) That "rattling" can break the metal parts it affects.
A lot of times in an engine with overly high compression, the timing is retarded to control the pinging. You can also use a much higher octane fuel, or a combination of the two.
You may want to take a closer look at the head you're using. It may be a different configuration that was designed for use with a different piston which would have produced a lower compression.
Hope this helps,
Bob
In terms of the preignition/pinging:
In an engine the piston travels up on compression. Before it reaches top dead center (TDC) the spark ignites the fuel/air. When the spark occurs is controlled by your setting for the ignition timing. Before the piston reaches TDC a certain amount of expansion of the fuel/air occurs adding to the compression inside the combustion chamber. If the ignition is set too far advanced or if the compression which you're measuring is too high, the pressures inside the chamber get too high and a dieseling effect occurs before the piston can start back down and the valves open to relieve the pressure in the combustion chamber.
Instead of a slow burn across the combustion chamber from a single flame front originating at the spark plug, you have two fronts. One from the spark plug and another from the dieseling effect. When the two fronts collide you have a ping which essentially rattles the metal parts (valves and piston, etc.) That "rattling" can break the metal parts it affects.
A lot of times in an engine with overly high compression, the timing is retarded to control the pinging. You can also use a much higher octane fuel, or a combination of the two.
You may want to take a closer look at the head you're using. It may be a different configuration that was designed for use with a different piston which would have produced a lower compression.
Hope this helps,
Bob
#6
03-12-07, 06:14 PM
It would vary for different engines and problems that made that particular engine ping.
To use timing as a remedy you would first need to be able to recognize the ping or spark knock. Usually you would notice it when you accelerate.
Once you are able to recognize the sound you can retard the timing a little at a time until it disappears. Some can hear the ping more readily than others.
If you go 3 to 5 degrees and you still have the problem, I would look at other remedies. You can get into starting problems if you "detune" the engine too much.
Other remedies would be repairing the engine to reduce the compression or using a different fuel. The latter would obviously be the easiest to try.
Good luck,
Hope this helps,
Bob
To use timing as a remedy you would first need to be able to recognize the ping or spark knock. Usually you would notice it when you accelerate.
Once you are able to recognize the sound you can retard the timing a little at a time until it disappears. Some can hear the ping more readily than others.
If you go 3 to 5 degrees and you still have the problem, I would look at other remedies. You can get into starting problems if you "detune" the engine too much.
Other remedies would be repairing the engine to reduce the compression or using a different fuel. The latter would obviously be the easiest to try.
Good luck,
Hope this helps,
Bob
#7
03-18-07, 11:11 AM
I plan on just putting higher octane or just buying regular gas and put octane booster and mix them together.
Does anyone know where i can find a gear reduction starter or a high cranking amps Battery near portland or Ionia Michigan? For this quad.
Does anyone know where i can find a gear reduction starter or a high cranking amps Battery near portland or Ionia Michigan? For this quad.
#9
03-30-07, 05:33 PM
battery
I found out that the battery the i bought for both of the quads was not the right one. it was only pushing 128 amps. the one my dad is going to buy tommarow has 190 amps. this battery is made for the quad.
