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Showing results for tags 'compression'.
Found 14 results
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Can someone give me a quick verbal (walkthru) of how to "properly" perform a compression check. Bike is an 86. I have a pretty good idea of how to check the compression, but since it has been literally years since I've done one on anything, I just need a quick review of the procedure. Here's how I would do one. Once the motor is exposed, I would 1) remove all the spark plugs 2) short out all the spark plug wires to not harm the CDI box 3) connect gauge 4) at full throttle, crank the motor over until max pressure is observed on the gauge for each cylinder 5) if low one tests low (what would be low??), squirt a little oil in that cylinder chamber then recheck 6) record all results Good compression would be where no one cylinder is more than 10 off from any other. Add anything you think I missed or should know before proceeding. Thanks
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I have recently put a lot of money into this bike; new needles and seats, diaphrams from sirius, progressive springs, had the tci resoldered and new diodes put in and had my seat redone by Rick ( which turned out great by the way). Was still running crappy. Rechecked the compression that I thought was good. Not so good. 3 cylinders were in the 120's and the back right was 100. Long story longer there is some blackening in that cyclinder and my mechanic thinks its either a bad ring or bad spring on the valves. 11 hour job. Now I either rebiuld or get a decent used motor with good compression. Or sell for what I can with the new owner knowing what he is in for. With all the info that has been compiled on this site I am considering trying to fix this thing myself if the cost is reasonable, even though I have never pulled a motor before. Also wondering what the cost would be to do this, rebuild or used motor. Any imput would help my decision. Thanks Doug
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I read the VR tech article but it seems to have a lot missing, particularly when reinstalling. If my memory serves me correctly, although probably incompletely, there are quite a few hints or tips scattered around the thousands of threads on this forum thatt I don't recall the details and can't seem to find. There is something about: - using Locktite but was it the red stuff or the blue stuff? - what about torque on the 3 inside bolts and the 2 outside ones? - using a spray gasket remover instead of a scraper? - properly aligning the shift shaft or it won't work after getting it all together - the washer that fell out when I pulled the stator cover off? It has a lip on the inside edge and a couple of bends that would work like a compression spring. Which way should it go in? - before sealing, is it better to just pull the new wires through the case grommet in place or remove the grommet from the case first? There may be more but that is all I can think of now. Only 5 days before I want to leave for Nelson Kruzen the Kootenays. No pressure. -
I got this fine scoot today, it needs a little TLC but should make a fun toy. I found it at the curb with the trash while on my way to move a boat. It's got compression & spark so it should run.
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It's an 88 Venture. Owner is Trader. Bought it from somebody in Chicago this year. Ran like crap when he bought it. Smelled rich, but plugs don't show it. Wouldn't idle without the choke on. Thought to do a carb tune on it yesterday. Found #2 cylinder wasn't firing. Cleaned the carbs with spray cleaner and a bit of air. Eventually got # 2 to fire. Still ran like crap. Tried to do a carb tune. ( I have a homemade one that has 1 vacuum gauge with 4 shut-offs that works just fine when ever I used it before and tests out just fine right now). Got no vacuum on # 2 or # 1 cylinders. Could get vacuum to show on 3 and 4 but the screws had to be turned to their max. Tried adjusting the throttle cables, worked better but didn't do anything for vacuum. Checked for leaks in the manifold boots, around the intake, around the airbox, and anywhere else that might be of interest. Called Squidley out of bed and found out what Lonna was up to,,, and it wasn't making cheesecake, so we talked instead,,,, thanks Lonna. Went out and convinced Steve (Trader) that it was time to get a compression tester. I bought it, he paid for it and then left it here???????? Compression tested to 180 on all four cylinders. engine was warm, not hot. Switched the vacuum lines form side to side to make sure things worked right. Expected to see #3 and #4 drop in vacuum, but 1 and 2 still didn't have any vacuum. Far as that goes, they seemed to maybe even have pressure because the needle seemed to keep wanting to go past the stop post. Set the screws to where I thought they would be most beneficial, (no vacuum showing anywhere) put it all back together, fixed the battery lead and put the tools away. End result: garage is cleaned up, bike runs without choke but still smells rich and idle screw is turned into the limit, Steve is on his way home and hasn't come back yet. I am now the proud owner of a brand new compression tester. AND WE NOW KNOW THAT 1ST GENS DON'T REALLY NEED VACUUM TO RUN! Now the big question,,,,,,,,,,,WHY??????? -
The other day I ran into a guy that needed to sell a 1983 venture that his father in law had sent down to him from PA. he didn't want it because they were getting ready to move. timing is a great thing, I picked this bike up for $1000 and it only had 24000 actual miles on it, garage stored the whole time not even a scratch. the carbs were gummed up, I went through them, checked the compression it was good 130psi on each cylinder, good spark but still runs like it is only running on half the cylinders. sluggish week. if any one has any suggestions on what to check for nest, PLEASE tell. and Thank You for all for the great website. Steve
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I just picked up a '96 Royal Star with only 19k on it, bike is in great shape except for one thing... I have a pop through the exhaust. I suspected a lean cylinder and was right (on part of it) so off with the carbs for a thurough cleaning. I installed them back on yesterday and dialed everything in, huge difference in performance... but still had the pop. At idle its a rythmic; Pop.... Pop.... Pop.... Pop.... but goes away when revved and comes back again if the rpm is held constant. So today I checked that cylinders carb for any leaks or possible cause for this issue, nothing found. Plenty of fuel there. I went ahead and did a compression test on both right side cylinders and they seem low to me, or at least what the manual says they should be. Cylinder compression test shows 110psi on the front right and 125 on the rear right. Spark plug was wet on the front so I dried the cylinder out and cleaned the plug... same pop and same compression reading. After this I ran a leakdown test and im just a bit over 20% loss coming out of the exhaust valves! This afternoon I'll pop the valve cover and check the valve clearance but im afraid the damage has been done and the adjustment won't help. My question is, what is a normal compression reading for these engines? And can the heads come off without pulling the engine? Thanks for any help, -
The front bank is not working. Cleaned the carbs twice and the bowls fill up. Has great fire. Hooked up the carb sync tool and it showed equalish vacuum on four. That leads my to believe they are pumping air at least. Other little thing noticed is the tach is not reading anything. Tryed several different tci boxes. (thanks dad) Also installed other coil pack we had. Going to find my compression tester tuesday or so. But since dads bike is running again I should get some more help. The bike is stripped of all plastic but believe only accs are unplugged right now. Thanks Brian -
There have been a couple threads recently about potential valve or ring damaged engines (yet to be verified). Harbor Freight has a Cylinder leak-down tester for $35 http://www.harborfreight.com/cylinder-leak-down-tester-94190.html or a simpler compression tester for $20. http://www.harborfreight.com/compression-test-kit-66216.html Would these be worth while to buy for local maintenance days, or for Freebird's MD? Who has used these devices, and how long does it take to test all 4 cylinders with one? Is there enough need or interest in testing compression to make this worthwhile? http://www.harborfreight.com/media/catalog/product/cache/1/image/370x/9df78eab33525d08d6e5fb8d27136e95/i/m/image_6165.jpg
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Hey all, I did compression check on my 96 RS and found low compression in cylinder #1. Added a little oil to see if it was rings or not and it made no improvement. The motor has 18k miles on it. I talked to the dealer I work with but his proposal is TOO open ended. I dont want to wind up with a $1500.00 + bill without knowing first. I live in Pa. Looking for an alternative to the dealer. -
I have a 1985 that starts and runs great, but it has a miss at idle. Cyclinder #2 has low compression (about 65 psi) I think it is the rings because after I put a little oil in the cylinder the compression went up to 100 psi. I can not find new piston rings anywhere. My question is do I replace the engine or just ride that way. It goes down the higway just fine and gets 38 mpg. I bought it last fall with 45600 miles on the odometer I'm thinking that was 145600 miles? The local salvage yards want $500 to $1000 for an engine. Does anyone here know of a source for rings for these bikes? Thanks in advance for your help, Randy
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Go figure spent all last summer rebuilding my bike after it got smashed up. Had two good rides out of it before parking it for the winter. yesterday. I changed the oil and filter fired it up to go for my first long awaited ride for the seaso and wouldn't you know it, an engine miss put my hands on the exhaust pipes and the left front one is stone cold , YUP a dead cylinder I put a spark tester in line with the plug and opened the gap to test spark strength and was over 1 inch and still getting strong spark jump across the gap. pulled the plug and although it was black it was not wet like a misfiring plug would normally be. going to do a compression test todayand see what my compression is. I sure hope it isn't some delayed damage from when the bike went down.
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I have little to no vaccum on one cylinder on the 86. It will not read on the carbtune, althou you can feel a little on the tube at manifold and if you take the restrictor out the rod will move up about an inch and bounce. I did a compression check this evening and all cylinders were around 200 plus or minus 4 lbs., which the manual says 199 is the high side with 142 being minumum and 171 standard. I have tried spraying WD40 around the carb boots with no rise in rpm. I checked the tube at manifold with a torch cleaning tip and felt no obstructions. All this was advice from Muffinman, Jeff I rechecked the compression on 1 and 2 only turning it over 3 times and the front cylinder read 150 and the rear 90lbs. Any one else have any suggestions?????????
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Both of these subjects have been under a lot of discussion lately, and my bike needed both. Saturday was the big day, and here is my story. I'll start with the clutch. What happens to these things that makes them slip without wearing? All discs measured exactly the same as the brand-new discs - no measurable wear whatsoever. Spring measured within spec. Yet I had mild slippage sometimes under full throttle (not very bad, but annoying). I put the new discs in anyway. Didn't touch the half-disc in the "damper" mechanism as the manual says not to unless there is "severe chatter". I didn't sand the plates or replace the spring. Now after about 40 miles of riding and quite a bit of full throttle. I have experienced no slip - hooray. I've experienced this before. I've had (3) 87 Yahamas. I've had a Virago for a long time, and WAY back I had exactly the same problem with the clutch. I recall measuring the old discs to be well withing spec, just like this time, replaced them anyway, and I've never had that clutch slip again in 80,000 more miles. The mileage on it at the time was probably in the 50k's, same as the Venture now. I also had a Radian for awhile with less than 20k miles on it, and it's clutch slipped on occasion. I never worked on it and then sold it. What's up with that??? While I had the cover off I removed the nasty old remains of clear coat and polished - looks way cool but now the other case covers look very bad comparision - they feel embarassed, too. Worst part of the job was removing the old, rock-hard gasket from the cover. Replacing the slides went about as expected. I didn't want to remove the carbs so I haven't looked at the coasting diaphragms, just the slides. I had pulled #3 and it was quite cracked, so I ordered (4) of them. I found that #2 had been replaced sometime, don't know when but it was at least 2 years ago, probably longer. The diaphragm was good on it. At $55 a shot I wish I had known that before ordering, but the rubber was a little harder on it than on the new ones so I just put in the whole matched set and will keep the "new-old" one around for a spare. This profoundly affected the tuning of the bike. The carbs, which I just synced a couple k-miles ago, were way out, and the pilot screws which I had also adjusted needed to be leaned out. This gives me hope that this will answer my poor MPG question. Everybody said bad diaphragms kills the top end power, so I was looking forward to knocking my socks off on the first ride, although it ran pretty good before. Well, my socks are still on, but I think top-end is up. It sure gets up and goes. For one thing, it seemed to be running out of steam at 100 before, and this morning I saw 110 mph with a little still left (ran out of room). OTOH, it may have been clutch slippage or aprehension of a weave that kept me below 100 before, so I'm not totally sure if my perception is accurate. It tachs out to 8k rpm with no problem. I'll let you know about the MPG, although all this WOT ain't gonna be too good on that! Finally, I had gotten some weird compression readings before which made me wonder if something inside the engine was about smoked. I preferred to deny it rather than think much about it. On Saturday I ran compression again with the engine HOT and new schrader valves in my gage hoses (I tried two gages). I got 190 to 200 psi in all cylinders - wow! I concluded the following: 1) A hot engine can make a difference in reading consistency. It also makes a difference in burned fingers. 2) There is a schrader valve in the end of the gage hose that need replacing on occasion. It is special, so don't install a regular tire valve core (it looks the same) - get it from a tool store. It has a profound effect on readings! 3) Different gages sometimes read differently, so use the same gage for your whole test. 4) Even the different hoses made 10psi difference. Both had new schrader valves. All I can figure is that the valves were slightly different, but I didn't take the time to swap the new valve cores and retest. 5) They say to open the throttle all the way, but on a CV carb that leaves the slide blocking most of the intake path. I removed the air filter and used a dowel to hold the slide open for the test (as well as opening throttle). This seemed to make about a 5psi difference, and allowed the compression to build a little faster. I wouldn't say it's a critical part of the test, but it did affect the test. Jeremy
