compression
#1
09-19-2012, 10:05 AM
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compression
I resently did a top end job on my 73xlch 1000 sportster.ive put cams in w marks lined up,but have no compression in frt cyl.,and only 85 psi in rear cyl.ive stabbed cams 3 more times w same results.was told that its poss that factory mark on cam could be wrong.is this true? I also changed pistons n rings,cyl bored to pistons.will this raise my compression psi going w bigger pistons?
#2
09-19-2012, 12:13 PM
first try checking the compression with the pushrods removed. that will tell you if the cylinder is holding in the first place..
then a leakdown test will tell you a lot about the engine and where the compression is going..
could easily be maladjusted pushrods, or leaking valves..
the slightly bigger (.010) piston isn't going to make much difference, but the fresh bore will.
rings could be wrong or broke..
it wouldn't be the first motor assembled with no/bad gaskets by mistake..
then a leakdown test will tell you a lot about the engine and where the compression is going..
could easily be maladjusted pushrods, or leaking valves..
the slightly bigger (.010) piston isn't going to make much difference, but the fresh bore will.
rings could be wrong or broke..
it wouldn't be the first motor assembled with no/bad gaskets by mistake..
Last edited by j1mmy; 09-19-2012 at 12:15 PM.
#3
09-19-2012, 02:50 PM
For the compression test the engine must be at full opereating temoperature [take it for a ride, not warm up in the shop] and the throttle and choke plates must be held fully open [choke **** in, throttle grip twisted fully]. Then i would check pushrod adjustment. Finally a leakdown test. Here are some notes ...
Cylinder Compression And Leakage Tests
A compression test should be done as part of each tuneup. Record the results and follow any changes over time.
A cylinder leakage test should be done any time you are considering taking down the top end. This test gives you useful information regarding what you should look for when you have it apart.
Each of these requires a tester which you can buy at an auto parts store. A compression tester could be found for about $40.00 more or less, and a clyinder leakage tester for somewhat more than that amount. With the cylinder leakage tester you will also need a small air compressor. Should be able to find a small sausage style for under $100.00.
Use these tools once and they have paid for themselves, compared to paying $50.00 to $100.00 per hour at a shop. Buy a slightly larger air compressor [look for about 5 CFM @ 90 PSI] and you will be able to use it with air tools.
Compression Test
1. Ride the bike to get the engine to get it up to operating temperature
2. Disconnect and remove both spark plugs; insert them into the leads and place them on the cylinder heads for grounding
3. Screw the compression tester into the spark plug hole for either of the cylinders
4. Hold the throttle open, and ensure the choke plate is also open [choke **** pushed in]
5. Crank the engine through several rotations until there is no further increase in reading at the tester gauge
6. Record the final reading
7. Repeat for the other cylinder
The difference between the two readings should not be more than 10 psi. A low reading on one cylinder indicates possible valve or ring damage to that cylinder. To determine which, pour about 1/2 oz of oil into that cylinder through the spark plug hole and repeat the test. If the reading returns to normal then valves are good, rings may be defective. If compression does not return to normal then valves may require service.
Cylinder Leakage Test
This test will tell you what to look for at the top end tear down: worn exhaust valves, worn intake valves, leaky head gaskets, or worn rings.
This test is usually done immediately following a compression test. So the engine is at or close to normal operating temperature, and the spark plugs have been removed.
1. Remove the pushrods to ensure that the valves are closed.
2. Set the cylinder to be tested at or near top dead center [TDC] as this is the wear area for the rings ...
a] rear wheel off the ground, shift to 2nd gear, rotate wheel until it clicks, repeat until you get to 4th gear. Now by rotating the rear wheel you are rotating the engine. Almost impossible with the plugs in; very difficult in lower gears. For the following it helps to have either a shop assistant or a wide "wingspan".
b] you can see in thru the spark plug hole, especially with a flash light. You can also try inserting something soft like a pencil and watch it rise and fall as you rotate the engine with the back wheel; but be careful it does not break or get stuck! You will have to hang on to the pencil with left hand while rotating the rear wheel with the right.
3. Turn on the compressor, connect the gauge to the air pressure, and adjust the gauge
4. Thread the adapter into the spark plug hole and attach to the gauge
5. The gauge now shows the amount of leakage
6. Listen at each exhaust pipe. Excessive hissing here indicates the respective exhaust valve is not sealing
7. Listen at the A/C intake. Excessive hissing here indicates intake valve[s] not sealing
8. Listen at the timing plug hole. Excessive hissing here indicates the rings are not sealing
9. Listen around the cylinder/head connection. Excessive hissing here indicates the respective head gasket is not sealing
Notes
A mechanics stethoscope [with the probe removed for this test] makes a good listening device, as does a length of oil line hose.
Greater leakage results in a sound of lower pitch.
There will always be some leakage, especially past the rings.
Ironhead Push Rod Adjustment
Do this procedure with the engine stone cold. I usually do it first thing in the morning.
1. Remove the spark plugs. Remove A/C to make room to work.
2. Using a flat blade screwdriver pry the spring keeper off of each push rod; the bottom of the keeper pops out first, then the top. Alternately, use a 3/4" open end wrench to push down on the top of the spring retainer, then pry out the spring keeper with the screwdriver.
3. The lower push rod covers may be stuck tight against the bottom o-rings, but they can be loosened by pinching between thumb and finger [or carefully using a shop rag and a pliers] and twisting or rotating. Lift these up and secure each with a tall-S-shaped piece of 12 or 14 gauge household wire [not cable] [or a long piece of Plumbers solder such as 95/5 hooked over the rocker cover and under the push rod cover.
4. Jack up back end of the bike so that rear wheel is off the ground, shift to 2nd gear, rotate wheel until it clicks, repeat until you get to 4th gear. Now by rotating the rear wheel you are rotating the engine. Almost impossible with the plugs in; very difficult in lower gears.
5. To adjust a particular push rod, its valve must be fully closed [the valve spring is relaxed]. Valve position for a particular cylinder is determined by observing the corresponding push rod of the other cylinder. For example, when the rear cylinder intake valve tappet is raised [valve fully open, spring compressed], the front cylinder intake valve is fully closed, and the front intake push rod can be adjusted.
6. Check [and adjust if necessary] the push rods:
[a] use the rear wheel rotate the engine so that the rear cylinder exhaust push rod tappet is fully raised. The front cylinder push rod is adjusted correctly if it has no vertical or horizontal play, and you can just rotate the push rod between thumb and forefinger with no trace of binding or dragging.
[b] to adjust if needed: hold the adjusting screw in place with a wrench; with another wrench loosen the split locknut. Then turn the adjusting screw using fingers only until the pushrod's ball end is seated in the tappet with a "slight amount of play". Then tighten further as follows:
Option 1: Adjust on the tighter end of the range: There should be no vertical or horizontal play, and you should be just able to rotate the push rod between thumb and forefinger with no trace of binding or dragging.
Option 2: Adjust on the looser end of the range: Set the adjusting screw to finger tight so that you cannot turn the push rod between forefinger and thumb. Undo it a tiny bit so that it is just barely loose. Then loosen it 1 "side" for an exhaust or 1/2 "side" for an intake. "Side" refers to one side of the 6-sided adjusting nut.
EDIT: Experience here is that Option 2 is the better and most likely the correct choice.
[c] hold the adjusting screw in place with the one wrench; with the other wrench tighten the locknut.
[d] recheck the adjustment; it is common for the adjustment to go out as you do step [c], in which case [b] and [c] must be redone.
[e] repeat for the other push rods.
7. Use a flat blade screwdriver to push the upper push rod covers up, and seat them into the upper o-ring or cork washer.
8. Install the spring keepers, top end first, by prying them in under the bottom with a flat blade screwdriver.
Cylinder Compression And Leakage Tests
A compression test should be done as part of each tuneup. Record the results and follow any changes over time.
A cylinder leakage test should be done any time you are considering taking down the top end. This test gives you useful information regarding what you should look for when you have it apart.
Each of these requires a tester which you can buy at an auto parts store. A compression tester could be found for about $40.00 more or less, and a clyinder leakage tester for somewhat more than that amount. With the cylinder leakage tester you will also need a small air compressor. Should be able to find a small sausage style for under $100.00.
Use these tools once and they have paid for themselves, compared to paying $50.00 to $100.00 per hour at a shop. Buy a slightly larger air compressor [look for about 5 CFM @ 90 PSI] and you will be able to use it with air tools.
Compression Test
1. Ride the bike to get the engine to get it up to operating temperature
2. Disconnect and remove both spark plugs; insert them into the leads and place them on the cylinder heads for grounding
3. Screw the compression tester into the spark plug hole for either of the cylinders
4. Hold the throttle open, and ensure the choke plate is also open [choke **** pushed in]
5. Crank the engine through several rotations until there is no further increase in reading at the tester gauge
6. Record the final reading
7. Repeat for the other cylinder
The difference between the two readings should not be more than 10 psi. A low reading on one cylinder indicates possible valve or ring damage to that cylinder. To determine which, pour about 1/2 oz of oil into that cylinder through the spark plug hole and repeat the test. If the reading returns to normal then valves are good, rings may be defective. If compression does not return to normal then valves may require service.
Cylinder Leakage Test
This test will tell you what to look for at the top end tear down: worn exhaust valves, worn intake valves, leaky head gaskets, or worn rings.
This test is usually done immediately following a compression test. So the engine is at or close to normal operating temperature, and the spark plugs have been removed.
1. Remove the pushrods to ensure that the valves are closed.
2. Set the cylinder to be tested at or near top dead center [TDC] as this is the wear area for the rings ...
a] rear wheel off the ground, shift to 2nd gear, rotate wheel until it clicks, repeat until you get to 4th gear. Now by rotating the rear wheel you are rotating the engine. Almost impossible with the plugs in; very difficult in lower gears. For the following it helps to have either a shop assistant or a wide "wingspan".
b] you can see in thru the spark plug hole, especially with a flash light. You can also try inserting something soft like a pencil and watch it rise and fall as you rotate the engine with the back wheel; but be careful it does not break or get stuck! You will have to hang on to the pencil with left hand while rotating the rear wheel with the right.
3. Turn on the compressor, connect the gauge to the air pressure, and adjust the gauge
4. Thread the adapter into the spark plug hole and attach to the gauge
5. The gauge now shows the amount of leakage
6. Listen at each exhaust pipe. Excessive hissing here indicates the respective exhaust valve is not sealing
7. Listen at the A/C intake. Excessive hissing here indicates intake valve[s] not sealing
8. Listen at the timing plug hole. Excessive hissing here indicates the rings are not sealing
9. Listen around the cylinder/head connection. Excessive hissing here indicates the respective head gasket is not sealing
Notes
A mechanics stethoscope [with the probe removed for this test] makes a good listening device, as does a length of oil line hose.
Greater leakage results in a sound of lower pitch.
There will always be some leakage, especially past the rings.
Ironhead Push Rod Adjustment
Do this procedure with the engine stone cold. I usually do it first thing in the morning.
1. Remove the spark plugs. Remove A/C to make room to work.
2. Using a flat blade screwdriver pry the spring keeper off of each push rod; the bottom of the keeper pops out first, then the top. Alternately, use a 3/4" open end wrench to push down on the top of the spring retainer, then pry out the spring keeper with the screwdriver.
3. The lower push rod covers may be stuck tight against the bottom o-rings, but they can be loosened by pinching between thumb and finger [or carefully using a shop rag and a pliers] and twisting or rotating. Lift these up and secure each with a tall-S-shaped piece of 12 or 14 gauge household wire [not cable] [or a long piece of Plumbers solder such as 95/5 hooked over the rocker cover and under the push rod cover.
4. Jack up back end of the bike so that rear wheel is off the ground, shift to 2nd gear, rotate wheel until it clicks, repeat until you get to 4th gear. Now by rotating the rear wheel you are rotating the engine. Almost impossible with the plugs in; very difficult in lower gears.
5. To adjust a particular push rod, its valve must be fully closed [the valve spring is relaxed]. Valve position for a particular cylinder is determined by observing the corresponding push rod of the other cylinder. For example, when the rear cylinder intake valve tappet is raised [valve fully open, spring compressed], the front cylinder intake valve is fully closed, and the front intake push rod can be adjusted.
6. Check [and adjust if necessary] the push rods:
[a] use the rear wheel rotate the engine so that the rear cylinder exhaust push rod tappet is fully raised. The front cylinder push rod is adjusted correctly if it has no vertical or horizontal play, and you can just rotate the push rod between thumb and forefinger with no trace of binding or dragging.
[b] to adjust if needed: hold the adjusting screw in place with a wrench; with another wrench loosen the split locknut. Then turn the adjusting screw using fingers only until the pushrod's ball end is seated in the tappet with a "slight amount of play". Then tighten further as follows:
Option 1: Adjust on the tighter end of the range: There should be no vertical or horizontal play, and you should be just able to rotate the push rod between thumb and forefinger with no trace of binding or dragging.
Option 2: Adjust on the looser end of the range: Set the adjusting screw to finger tight so that you cannot turn the push rod between forefinger and thumb. Undo it a tiny bit so that it is just barely loose. Then loosen it 1 "side" for an exhaust or 1/2 "side" for an intake. "Side" refers to one side of the 6-sided adjusting nut.
EDIT: Experience here is that Option 2 is the better and most likely the correct choice.
[c] hold the adjusting screw in place with the one wrench; with the other wrench tighten the locknut.
[d] recheck the adjustment; it is common for the adjustment to go out as you do step [c], in which case [b] and [c] must be redone.
[e] repeat for the other push rods.
7. Use a flat blade screwdriver to push the upper push rod covers up, and seat them into the upper o-ring or cork washer.
8. Install the spring keepers, top end first, by prying them in under the bottom with a flat blade screwdriver.
#4
09-21-2012, 06:48 AM
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Thks for the info.it will help in the future.although ive already have cams out again.i dont seem to have a problem stabbing them with all the marks lined up.but it seems like even though markings are in line ,i still have no compression in frt n 85 in rear.i was told compression should b round 120 n a 10 pnd difference in both cycl is acceptable.which if thats true.then my rear cyc comp. Is leaking also.correct? Im not sure which direction to go.ive done stabbed cam numerous times w same results.
#5
09-21-2012, 07:50 AM
I have not seen this terminology "stabbing" before. Do you mean simply installing them? Do you have the pinion gear mark also lined up? Here's my PB+ cams lined up; note the pinion gear mark which is sometimes hidden by the tabbed lock washer ...
I start with the pinion gear mark at about the 11:00 o'clock position then install cam #2, then rotate the engine until those two marks are perfect. Then temporarily uninstall #2 while i install #1; then install #3 and #4.
If cams are correctly lined up, and pushrods correctly adjusted, and compression test done with engine at full operating temperature and throttle open, then it would appear that a valve in the front cylinder head is not closing. 120 in the rear cylinder does not necessarily indicate any problem other than normal wear.
You have done what you can without taking off the top end for inspection. If you have not done this before i will pass on some more info. It is not a difficult job to do.
Do you have both of factory service manual 99484-78 and factory parts catalog 99451-78B? These are essential tools and are widely available from a local indie bike shop, HD dealer, J&P Cycles, and various internet and eBay sellers. Just put the part numbers into the Google and eBay searches.
I start with the pinion gear mark at about the 11:00 o'clock position then install cam #2, then rotate the engine until those two marks are perfect. Then temporarily uninstall #2 while i install #1; then install #3 and #4.
If cams are correctly lined up, and pushrods correctly adjusted, and compression test done with engine at full operating temperature and throttle open, then it would appear that a valve in the front cylinder head is not closing. 120 in the rear cylinder does not necessarily indicate any problem other than normal wear.
You have done what you can without taking off the top end for inspection. If you have not done this before i will pass on some more info. It is not a difficult job to do.
Do you have both of factory service manual 99484-78 and factory parts catalog 99451-78B? These are essential tools and are widely available from a local indie bike shop, HD dealer, J&P Cycles, and various internet and eBay sellers. Just put the part numbers into the Google and eBay searches.
#6
09-21-2012, 08:41 AM
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#7
09-21-2012, 11:44 AM
120 is minumum for a good engine. Down to 90 or so is OK if the engine is running reasonably well, but we plan on doing the top end as a winter project. A new top end will have 150 to 180 psi.
The parts catalog is handy as it shows all the exact correct parts, has all the part numbers, and the diagrams showing how all the parts fit together. Then you do not have to wonder if you are looking at the real thing or whatever a previous owner might have done; and you can search the internet, eBay, etc for parts - you always need the part number for this.
Before proceeding it would be a good idea to get more opinion. Best would be to post the stiuation on this other IronHead forum ...
Ironhead Sportster Motorcycle Talk (1957-1985)
http://xlforum.net/vbportal/forums/forumdisplay.php?f=7
There are more guys there with more experience. I expect that you will need to take off the rocker covers and cylinder heads, and probably the cylinders; post pics on the forums; then probably take the heads and cylinders to a machine shop for evaluation. For this you will want to find a shop that has lots of experience working with vintage engines - the shops that work with modern engines will not do the job right, regardless of what they say.
Post in the other forum first.
The parts catalog is handy as it shows all the exact correct parts, has all the part numbers, and the diagrams showing how all the parts fit together. Then you do not have to wonder if you are looking at the real thing or whatever a previous owner might have done; and you can search the internet, eBay, etc for parts - you always need the part number for this.
Before proceeding it would be a good idea to get more opinion. Best would be to post the stiuation on this other IronHead forum ...
Ironhead Sportster Motorcycle Talk (1957-1985)
http://xlforum.net/vbportal/forums/forumdisplay.php?f=7
There are more guys there with more experience. I expect that you will need to take off the rocker covers and cylinder heads, and probably the cylinders; post pics on the forums; then probably take the heads and cylinders to a machine shop for evaluation. For this you will want to find a shop that has lots of experience working with vintage engines - the shops that work with modern engines will not do the job right, regardless of what they say.
Post in the other forum first.
Last edited by IronMick; 09-21-2012 at 11:46 AM.
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#8
09-21-2012, 11:52 AM
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#9
09-21-2012, 09:30 PM
Outstanding HDF Member
I am assuming you have adjusted the pushrods correctly. Have you?
If you have them too tight, then the valves will never close resulting in no compression at all or a very low compression.
If you did like Jimmy suggested and removed the pushrods to check compression then that is not going to work for you because all the valves are closed all the time.
No way for air to be drawn into the cylinders if the valves don't open.
So make sure the pushrods are adjusted by the book and then do a compression check again.
Open the throttle wide open and hold it there while you kick over the engine 4 or 5 times.
Do this for both cylinders and if the readings are still 85 psi on the rear and zero on the front then you have big problems in the top end and you will have to remove the heads.
Turn them upside down and fill with water.
Good valve seating will hold the water overnight.
If that head that reads zero is filled with water then I expect it will run out as fast as you fill the head cavity. The problem being the valves are not seating.
pg
If you have them too tight, then the valves will never close resulting in no compression at all or a very low compression.
If you did like Jimmy suggested and removed the pushrods to check compression then that is not going to work for you because all the valves are closed all the time.
No way for air to be drawn into the cylinders if the valves don't open.
So make sure the pushrods are adjusted by the book and then do a compression check again.
Open the throttle wide open and hold it there while you kick over the engine 4 or 5 times.
Do this for both cylinders and if the readings are still 85 psi on the rear and zero on the front then you have big problems in the top end and you will have to remove the heads.
Turn them upside down and fill with water.
Good valve seating will hold the water overnight.
If that head that reads zero is filled with water then I expect it will run out as fast as you fill the head cavity. The problem being the valves are not seating.
pg
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