Question about 1976 Ducati 860 GTS

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I have an 860 GT and want to know the ideal compression pressure

I have an 860 GT and is about due for a top end rebuild. Prior to dismantling what should the compression pressure be in an 860 GT, for example 155 PSI

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You're asking a BAD question in my opinion. I'll explain, and give you a FAR better solution... Compression checks in my opinion are fine for checking from cylinder to cylinder ONLY. If you're within 10 psi plus or minus, you're fine. However, cylinder LEAKDOWN will tell you if you've got an issue. You may have good compression, but any compression readings will not show leaks in the valvetrain unless the leak is pretty bad. I would instead test cylinder leakdown both cold and hot using a leak down tester, a good air compressor with a good regulator, and if you have anything worse than 85% in a leakdown test, use your ears to find the air leak. If the leakdown says for example 70%, listen in the exhaust and through the carbs. If both are quiet, listen in the oil fill hole. Now not only do you KNOW how bad the issue is, you know right where it's at. Intake valve, exhaust valve, or piston/cylinder. the Stick

Posted on Dec 10, 2009

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2001 Scrambler 400. What should compression reading be?

With the decompressor active, nominal is 85 - 90 psi. At 62 psi, you have a top end problem. Try dumping a bit of oil in the cylinder and re-test. If the pressure rises, you have a ring seal problem. That sounds like an top end rebuild.

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125-140 is Ideal, Not only do you want a higher compression but you also want them Balanced. The PTO (Clutch Side) normally will indicate a lower compression because it is the cylinder to go FIRST. So if that number is lower, you might be looking at a Top End Rebuild that is fairly easy to do. Anything less than 90, and you won't get a good fire going and normally will not fire below 70. hope this helps..

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There is always a better alternative than the dealership as far as costs. They want to put a new motor in a 2003 model? That is ridiculous to me- cost-prohibitive. Find a reputable independent shop. Look for references and customer satisfaction. A used, low mileage replacement engine is a better alternative, probably less than half the cost of a new engine.
There may be an even better alternative, where you refurbish the top end of the engine-the cylinder head and valve train. This is dependent on that a wet-dry compression test supports rebuilding the top end. What I mean by this is a compression test of the cylinders reveals low compression in one or more cylinders, okay. Next, they would squirt some oil (about a tablespoon) in the low cylinders and check compression again. If compression doesn't change, it points to the valves and valve train (the valve guides which wear and could let oil into the cylinder). But if compression is higher in the wet test, then the piston rings are worn and losing compression, and oil gets past them-this would indicate the engine needs a complete rebuild or a replacement is called for. The reason for the wet test is that the oil will temporarily seal around the piston rings and improve compression if the rings are the problem.
If the test shows the valves are the problem (and it is very possible on an engine with only 120K-your bottom end could be fine), then a top end rebuild of the engine is a much cheaper route than any other choices. You may not know this, but often a little oil burning in the cylinders at start-up is nothing more than the valve stem rubber seals are deteriorated-a real cheap fix. The dealership probably won't tell you this. However, with the loss of power, well, that points to something more severe than valve stem seals. So I would recommend the wet compression test, just to check if it is the top end or the bottom end. If it's the top end, you could have the cylinder head reconditioned and motor along for a few more years, trouble free.
Similar to a compression test, a "leak down" test of the cylinders is actually a more accurate method of finding where compression is lost, and it's only a one step test. They hold compressed air in the cylinder and analyze where it escapes to pinpoint compression loss. Loss of compression translates into loss of power. Have either test done before you decide. Find a good mechanic and trust his advice. (Stay far away from dealers. Greed is their motivating factor.)

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Dont waste your time looking for something else. Go ahead and pull the spark plug and do a compression test. It should have at least 100psi. If not,its time for a top end rebuild. It gets worse when it gets hotter because the ring gap expands,and loses what little compression it has. Best to check the compression and rebuild the top end now,before the piston or rings break,and cause lower end engine catastrophe...

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The fan is reaching end of life, or there is a lot of dirt build up in the cooling fan and the heatsink ports. The ideal way is to dismantle the laptop down to the motherboard, remove fan and heatsink use a can of compressed air blow all dirt from open ports and the cooling fan, and in most cases it will run better

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I have a problem with oil gushing out of the breather box of my sons susuki 160 2 wheel drive atv. can any one help.?any suggestions ?>it is an older atv with alot of miles .

If it has not been over filled with oil the it will most likely be to much blow by caused by the compression rings wearing out.
Do a compression test and check against the acceptable figures from your manual or a dealer.
If the compression is to low you will need to do a top end rebuild.

Feb 04, 2011 | Suzuki GSX 400 F Motorcycles

1 Answer

Only runs on one cyclinder even after i changed plus and cleaned carbs.

Assuming you have spark and know you're getting proper fuel, next we have to suspect compression. Assuming you don't have a compression gauge at this point, check your valve clearances. You may end up finding some out of spec, but you are specifically looking for valves that have no lash at all. If you find any like this, you will have likely found your problem. Adjust those valves and check it out. If it works, keep a check on that valve. If it keeps tightening up, you may need a new valve.

Next, again assuming you don't have a compression gauge, remove both plugs. Hold your thumb over the hole on the side that does hit and crank the engine over. Notice how hard it blows your thumb off. Now the other side. Does it feel as strong? This will only get you ball park, but usually when a cylinder is completely dead due to lack of compression, you can pretty easily tell a difference. If there is a difference, it's time to rebuild the top end.

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Jun 10, 2010 | 1977 Yamaha XS 650 D

1 Answer

What should the compression range be on a 2004 cr

compression range is 120-160 ok but anything under 120 needs top end,if not you will start to where on those cylinder walls with the ring

May 08, 2010 | 2004 Honda CR 125 R

2 Answers

Not starting

Hi there
  • Low compression, and lots of blow-by forcing oil into the air filter via the the crankcase breather. Sounds like you need a top end rebuild. If you can get your hands on a compression tester, then check it. If it comes in under 120, then certainly time for a tear down and top end rebuild.

  • If you put a quick squirt of oil down the spark plug hole and if the compression pressure goes up on a second compression test, then rings/piston/bore are worn. If it does not come back up, then it may be leaky valves, or a blown head gasket.

  • do the compression test first. That will tell you where to start. Or, if you have the tools, tear the top end down and inspect. A motor re conditioner/machine shop will help to measure up and tell you if piston, and bore are ok. May just need new rings to freshen up.

Happy to answer any questions that you may have.
regards robotek

Apr 25, 2010 | 2005 Honda CRF 250 R

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Since rebuilding the engine traction seems to be my major problem. the rebuild was done with Walter Wolfe racing specs. Compression is 8.8 to 1 with 32 flat slide carbs. Wheel spin is a problem especially...

Soften up the rear end a bit and /or drop the tyre pressure a little bit.A tiny drop in air pressure makes a really big difference.It puts a bigger wheel print on the road.Hope this may help you.

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