I lost compression in the front cylinder on my 1980 harley davidson,sportster. what could be the cause?

Question

the motor has no modifications. it has a super e carb. i was riding it when i noticed i lost alot of power.

Answer 1

it's a harley, that's your first problem....

Answer 2

Boy, try to ask a question and you end up with dipsnits like Joe B and Magz making stupid comments. I thought riding motorcycles was about having fun, not putting fellow riders down because you like different bikes. If you don't like Harleys then pass on.

Anyhow, back to your question. As others have mentioned check the basics first. If a compression check indicates low pressure go from there. One of the great things about Harley engines is that you can remove the top ends with the engine in the frame. You can put a new cylinder head and cylinder on in a few hours. You can rebore the cylinders and put in new pistons for under a grand (less then $600 if you do it yourself).

If you need help a great source for Sportster info is http://www.sportster.org/. They have an email list and the people over there are very helpful.

Answer 3

Did you check the cylinder with a compression test? Or did it just seem to quit firing? This looks to be a bummer and you maybe in for some real mechanical work. Complete{whole engine} tear down and rebuild. Start with the small stuff 1st and go from there.

Answer 4

1. Do a compression check to make sure that is the problem, if you haven't already.

2. Set the valve clearance and see if that helps.

3. If you still have no compression then you will need to pull the front head to see what happened

4. Look for a hole in the piston. Scored cylinder from a broken ring. A burned valve. A broken valve spring. A rocker arm that is galled and holding the valve open. Or if you are lucky a push rod that has jumped out of the lifter or rocker, but you should find that when you adjust the valve clearance.

5. Iron head sportsters are the easiest and the cheapest motorcycle there is to work on.

6.  Put the intake manifold on before tightening the head bolts so the intake will be aligned and wont leak on you.

7. Go to xlforum.net for a **** load of information on all models of sportster. Such as how to adjust every part of the little cast iron beast.

Answer 5

you have to take it apart and do a visible inspection

note:   its going to cost you a lot of money, its going to cost more to fix it than what the bike is worth

I say junk it, take your loss, and sell the bike for parts in e bay

Answer 6

Ryde on makes sense... you speak of a loss of power but it sounds like you could still ride... that's kind of at odds with compression loss.Valves and rings if they fail are going to cause something more catastrophic. Check as many things as you can from plug wires to plug to loose grounds etc. before pulling a head... comp check is easy with a guage in the plug hole.

Answer 7

You have whats known as an Ironhead Sportster

They have a few problems but overall, with proper maintenance are a fun bike....Stuff I would check first:

1. The 1000cc XL engine has Solid Lifters that require adjustments every 3000miles..Thats where I would look first, was the valve train unusually noisy? clicking or tapping sounds that were overlly louder then usual? if the lifters have not been adjusted in a long time they may have gotten loose enough to not open the valves properly.

2. You may have a blown Head or Base Cylinder gasket, this will not allow the cylinder to build compression.

3. An Intake manifold leaking air will cause an extreme lean condition in the cylinder, I have seen that actually allow the combustion of the spark plug burn a hole in the top of the cylinder, take the spark plug out and look through the hole with a good flashlite and see if there is anything in the top of the piston.

4. are you positive you lost compression, maybe its just a spark problem on the front cylinder, bad plug (fouled and not firing), bad plug wire, bad coil?

Even if it is as bad as a burnt piston, that is actually a fairly inexpensive repair, you can do it yourself for around $100-$125 in parts, and if you are unsure how to do it, a local Independent shop ( not a Harley Dealership, you won't find one that will work on your bike)  could probably do the job for maybe $300-$400 including their labor.

Good Luck and let us know what you found.

Answer 8

A quick guess would be a burned valve or piston.  However, it could be any number of things.

Whatever it is, a dramatic loss of compression is a symptom of an internal problem. You won't know for sure until you tear it down.  If you decide to repair it, you will need to tear it down anyway.

Once you get the cylinder head of of the cylinder that is causing problems, you will know for sure what it wrong.  Then you will be able to make a decision to either repair the problem or part out the bike and get a new one.

Answer 9

tear it down and have a look.... the only reason you need to leave it together at this point is if you decide you've had enough of it and sell it as a whole parts bike... even if you decide to part it out you still gotta take it apart.  

Answer 10

What makes you think it's due to a loss of compression ,rather than a loss of spark ?

A loss of compression could be caused by a damaged push rod , valve or ring , but it's more likely spark.

  

Answer 11

This could be a number of things. Check that the spark plugs is working (spark, fuel to cylinder) and seated home right. Check for leak at exhaust check valves are set right.Have a compression test done.Its a process of elimination.But before you start stripping it down check the above and if you cant do this leave it in to a good workshop.Best of luck