Where is my compression going?

Trying to get your Spree/Elite to run, or run better? Post your questions here.

Moderator: Moderator

Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Where is my compression going?

Post by Energizerspree »

I have just rebuilt an 84 spree motor, new bearings and seals all around, new belt, gaskets, and new cylinder and bore kit (still 49cc). I have spark, i test compression and its pathetically low, 40 ish. I made a home made leak down tester of sorts and found that the jug holds pressure. I spray a little carb cleaner directly in the cylinder and a little in the carburetor with the air box off. I figured I should at least be getting a sputter out of it but it doesnt seem to ignite the least bit. I dont totally trust my cheep compression tester but i can see spark, and the carb cleaner is there for that initial pop so maybe the compression tester is telling the truth. I had this problem so I got yet another cylinder and piston because i figured the rings were at fault. The second replacement yields the same results so i suspect it must be a problem somewhere other than the rings. Where could i be losing my cylinder compression other than the rings?
User avatar
jakubman1
Elite
Elite
Posts: 608
Joined: Sat Oct 24, 2015 9:33 am
Location: Tampa

Re: Where is my compression going?

Post by jakubman1 »

reeds ?
Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Re: Where is my compression going?

Post by Energizerspree »

I thought that too, so i checked them and they look good, and i rigged an air compressor with a rubber stopper, and i put a rubber stopper in the exhaust held in by a quick clamp. It all held pressure until the left side crank seal popped out.
User avatar
Meatball
CB900F
CB900F
Posts: 2320
Joined: Sat Jun 04, 2016 10:45 am
Location: seattle

Re: Where is my compression going?

Post by Meatball »

I think pressure testing a case is low pressure. Like 7-12psi? Cant remember exactly. Pat or Wheel would know...
I need to find some new haters...the ones I have are starting to like me.
Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Re: Where is my compression going?

Post by Energizerspree »

so my compression leak has to be either the rings or cylinder head then right? because the jug was holding like almost 90 psi before it popped out the left crank seal. i guess ill check and see if the head is warped.
User avatar
Meatball
CB900F
CB900F
Posts: 2320
Joined: Sat Jun 04, 2016 10:45 am
Location: seattle

Re: Where is my compression going?

Post by Meatball »

Its not likely the head is warped. Other components would fail long before temps would get hot enough to do this. Low compression in the combustion chamber (if you have one) is either loose head bolts, a failed head gasket or worn rings/damaged cylinder walls.
I need to find some new haters...the ones I have are starting to like me.
Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Re: Where is my compression going?

Post by Energizerspree »

head bolts are properly torqued, gasket is new, rings piston and cylinder are new. Every time i try to start it, if I look at the spark plug after it'll be wet. Does that mean anything?
User avatar
eclark5483
CB900F
CB900F
Posts: 1437
Joined: Thu Apr 14, 2016 5:15 am
Location: Spencer Iowa
Contact:

Re: Where is my compression going?

Post by eclark5483 »

What are you running for oil?
Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Re: Where is my compression going?

Post by Energizerspree »

I have honda synthetic in the tank, and about 50-1 in the fuel tank. Since the piston and cylinder is new i added the premix for the first tank to break it in. Thats what they recommended for breaking in the BBK on my other spree anyway. The gas is new.
User avatar
Meatball
CB900F
CB900F
Posts: 2320
Joined: Sat Jun 04, 2016 10:45 am
Location: seattle

Re: Where is my compression going?

Post by Meatball »

Energizerspree wrote: Every time i try to start it, if I look at the spark plug after it'll be wet. Does that mean anything?
Sure does! They say the eyes are the window to the soul...this rings true for spark plugs.

The triangle consists of fuel, spark and air. Wet spark plug proves you have fuel with a lack of one of the other two. Check for spark on your plug by having it hooked up to the coil wire and hold it close to one of the headbolts (or something else grounded to the bike). Then give the kickstart a few kicks to see if spark jumps to the host of choice. I suggest holding the rubber plug boot while doing this to avoid zapping yourself.

If theres NO spark. This could be from a severely worn plug, faulty coil wire, faulty CDI, stator, rectifier, etc...list goes on. If this is the case, the Service Manual has a series of simple tests with multimeter to check virtually every component. (except CDI, no test available, replace if faulty). If it DOES spark, youre still not out of the woods. Its possible your spark is weak! Run all the same tests and find out if youre losing voltage. Tests are easy, just poke the right spots and check if resistance is within spec per manual.

The other corner of the triangle is AIR. If you have fuel and spark but NO (or less than the needed amount of) air, it wont ignite. This would also result in a wet plug condition. The usual culprits being airbox/filter restriction, carbon plugged muffler or maladjusted carburetor.
I need to find some new haters...the ones I have are starting to like me.
Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Re: Where is my compression going?

Post by Energizerspree »

Ok, I do have spark but i suppose i should get my electrical tester on it to see if its powerful enough. I am fairly confident in my exhaust flow, I cleaned it out with carb cleaner, coat hanger wire and an air compressor.
User avatar
eclark5483
CB900F
CB900F
Posts: 1437
Joined: Thu Apr 14, 2016 5:15 am
Location: Spencer Iowa
Contact:

Re: Where is my compression going?

Post by eclark5483 »

You have too much oil. It was a stock sized piston, yes? 50:1+pump= minimum of 30:1 and even higher when RPM increases. You are over saturating that piston, probably fouling the plug. This is why when you test for spark it seems fine.
Energizerspree
Noob
Noob
Posts: 8
Joined: Mon Jun 19, 2017 3:05 pm
Location: wisconson

Re: Where is my compression going?

Post by Energizerspree »

Do you think I could test for that by removing the carburetor and just spraying a little carb cleaner in the intake? That would stop the gas flow and I could at least let it pop a couple of times without letting it actually run, just to confirm that the fuel is the problem before i drain the tank.
User avatar
eclark5483
CB900F
CB900F
Posts: 1437
Joined: Thu Apr 14, 2016 5:15 am
Location: Spencer Iowa
Contact:

Re: Where is my compression going?

Post by eclark5483 »

Just stick a rubber hose in a gas can, have it above the carb, the petcock should let it flow. Might have to rig it a bit, but then, why test, you ARE over saturating, no question about it. You don't need any extra oil then stock to break in that piston. It was never required when bought new at the dealer, no reason to think 30 years makes a difference.
User avatar
bonesv
Moderator
Moderator
Posts: 2128
Joined: Sun Jun 26, 2011 2:00 pm
Location: Florida

Re: Where is my compression going?

Post by bonesv »

Energizerspree wrote:I have just rebuilt an 84 spree motor, new bearings and seals all around, new belt, gaskets, and new cylinder and bore kit (still 49cc). I have spark, i test compression and its pathetically low, 40 ish. I made a home made leak down tester of sorts and found that the jug holds pressure. I spray a little carb cleaner directly in the cylinder and a little in the carburetor with the air box off. I figured I should at least be getting a sputter out of it but it doesnt seem to ignite the least bit. I dont totally trust my cheep compression tester but i can see spark, and the carb cleaner is there for that initial pop so maybe the compression tester is telling the truth. I had this problem so I got yet another cylinder and piston because i figured the rings were at fault. The second replacement yields the same results so i suspect it must be a problem somewhere other than the rings. Where could i be losing my cylinder compression other than the rings?
Why don't you start by being clear about your methods. Have you got this motor to fire yet? Has it run at all? When you check for compression, do you hold throttle wide open? How many kicks (revolutions) do you make to obtain a reading? What brand and number spark plug are you using? Is it new? Properly gapped to spec? The leak-down tester only requires a few pounds of pressure (6-8 psi) to check for leaks in the case, not the cylinder/rings. That's a different kind of tester for 4-stroke motors. What carburetor is on this motor? Is it the original (Keihin) from Honda? What size main jet is in the carburetor? Just because it's getting fuel doesn't necessarily mean it's working correctly. Have you cleaned this carburetor? Were any parts replaced? Is the air box sealed up and an oiled air filter in place?Spree's are very temperamental and if you have never rebuilt a small motor like this, it's possible that something has been overlooked, incorrectly installed, or accidentally damaged to cause a small issue. I'm suggesting that you double check with this list of questions to be thorough and hopefully you can get it running. A new motor will not usually have the full amount of potential compression until it has been properly broken-in so just test it with the throttle wide open the whole time during the compression test and if you do get it running don't go wide open or racing it until it's broken-in. Ask more questions and give as much information as you can to receive the best advice. Good luck!
Honda Elite SR
Honda Elite-Dio ZX

Dio ZX Headlight/Disc Brake Mod: http://hondaspree.net/phpBB3/viewtopic.php?t=30861
Post Reply