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high compression build problem
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Greg Riddle
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PostPosted: Sat Sep 28, 2013 8:27 pm    Post subject: high compression build problem Reply with quote

i have a honda vtx 1300. its a single crankpin v-twin. last winter i did an engine build on it and installed 11:1 pistons and bigger cams. the build went well the bike has a lot more power but im having an issue. since the install the front exhaust valve has ticked a lot louder than the others, the front cylinder is 20 lbs lower on compression the the rear cylinder and there is a slight squeak or whistle that accompanies the exhaust from the front cylinder. the front cylinder is running 180 psi and the rear is 200. the noise happens when i let off of the throttle. i have 8,000 miles on the build. runs fine except the posted issues. any ideas would be appreciated
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sat Sep 28, 2013 10:10 pm    Post subject: Reply with quote

not real familiar with that engine but first thing i would do is a valve adjust. have you checked the lash ?
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af2 wrote:
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Greg Riddle
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PostPosted: Sat Sep 28, 2013 11:43 pm    Post subject: Reply with quote

10sec.et wrote:
not real familiar with that engine but first thing i would do is a valve adjust. have you checked the lash ?


valve lash is correct set several times and even tried some out of spec settings
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Greg Riddle
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PostPosted: Sun Sep 29, 2013 12:07 am    Post subject: Reply with quote

also its not using oil or coolant. the only tings that are off are the noise coming through the exhaust, the loud valve tick and the low compression. i will probably tear down again and inspect. im thinking that its possible the cam timing might be off but im positive i put the sprocket back on correctly. i also lapped the valve but dont think that would cause any issues. maybe the exhaust valve got bent
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Big Dave
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PostPosted: Sun Sep 29, 2013 12:54 pm    Post subject: Reply with quote

The noise could be an exhaust leak.

As to the compression issue a difference of ten percent (1-180/200=0.10) implies an issue with maintaining a seal within the combustion chamber.

Since you are getting a ticking valve noise I could expect a bad seat or burnt valve. One other possibility that comes to mind is a defective spark plug seat or sealing washer under the spark plug if it seals that way.

Unfortunately I am not familiar with this engine either. I used to ride when I was younger; but I never owned a bike. I either borrowed by brother's Suzuki GSX-R1100, or a Harley Sportster from a friend, if I had to ride with someone. But in either case I never maintained the bike.

Big Dave
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clay
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1972 Chevrolet Nova

PostPosted: Sun Sep 29, 2013 4:33 pm    Post subject: Reply with quote

Quote:
Harley Sportster from a friend


I'm sorry Laughing . I would start with a leak down test. For what you are looking for you don't even need a tester, just some way to pressurize the cylinder in question. It's usually pretty easy to modify an old spark plug to use as an adaptor. All you're interested in is if there is any excessive leakage around the rings or any leakage around the valves. Some of what you're hearing could be carburetor related (assuming it's not fuel injected or course). It could possibly need a larger pilot or there could be a problem with the idle air cutoff diaphram (assuming it has one). I'm not famaliar with that particular motorcycle either but have owned / worked on / modified a pretty wide range of bikes. Welcome to Smokemup! Clay

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Greg Riddle
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PostPosted: Mon Sep 30, 2013 8:22 pm    Post subject: Reply with quote

thanks for the ideas. a leak down test may be very informative.
it may eliminate one of the 2 theories. i may be wrong but if i do a leak down test and it appears acceptable then my thoughts would lean more towards the cam for the front cylinder being off a little. if the leak down sucks i would lean more towards the valve or valve seat issue.

the thought that is pushing me towards the cam being off it there are 2 marks on the crank for aligning the front and rear cylinders at top dead center are only 1/8" apart. it is possible that i miss aligned the mark. i dont think i did but shit does happen.
i will try to work on the leak down test this weak. i just got a lower geared rear end for the bike so that bit of fun may take precedent


engine information

1312 cc (80 CI.)
single crank pin 52 liquid cooled v-twin.
single overhead cam
3 valves per cylinder
solid tappet rockers
2 spark plugs per cylinder
3 1/2" bore
4 3/32 stroke
9.2:1 compression stock. 11:1 now
cam info is propitiatory and the manufacturer will not give me the info.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Tue Oct 01, 2013 12:16 am    Post subject: Reply with quote

if leakdown is good, then cam timing seems the most likely culprit. however, it doesnt explain the noise unless you have more than one issue on the same cylinder. keep us posted. im not above learning something new.
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Greg Riddle
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PostPosted: Tue Oct 01, 2013 7:29 pm    Post subject: Reply with quote

ill keep posting info and ideas. i will not be doing the tear down until the snow starts flying. i dont want to give up my daily bike ride.

got my new final drive with the lower gear set. cant put it in because i thought a had a bottle of gear oil and dont Sad . will have to get one tom. i really wanted to play with it
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Greg Riddle
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PostPosted: Tue Oct 01, 2013 8:08 pm    Post subject: Reply with quote

here is a video of the engine running

http://www.youtube.com/watch?v=q6wZ7JaHGpw
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Greg Riddle
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PostPosted: Thu Oct 10, 2013 8:33 pm    Post subject: Reply with quote

well i did some testing the front exhaust valve is leaking. my theory is the exhaust valve is slightly bent. this problem has been there since the build started. this winter ill replace the exhaust valve. my question is should i replace the valve guide as well. or just the valve.

i also need to figure out a way to tear down the front cylinder without tearing down the rear. the rear cam is used to find tdc on the compression stroke on the front cylinder. i should be able to use other information to find the position info that i need
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Thu Oct 10, 2013 10:35 pm    Post subject: Reply with quote

make sure the valve seat hasnt moved. i would try lapping the valve and see what its doing. if its bent or the seat has moved, you will see it.
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Greg Riddle
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PostPosted: Thu Oct 10, 2013 10:52 pm    Post subject: Reply with quote

it will cost me $100 to replace the valve, valve guide, valve seal, retainer and clips. im going to get the parts and replace them.

i did find a way to tear down the front and leave the rear alone. the assembly procedure requires you to put the rear cylinder at tdc then look at the markings on the cam. there is an r stamped on the cam that is in the up position with the rear cylinder is on the compression stroke. when its not on the compression stroke the r is facing down. after you determine compression stroke or not you rotate the engine 412 , for tdc compression stroke, or 52 tdc at the end of the exhaust stroke. i can remove the valve lash inspection covers to determine cam position then rotate the engine either 412 or 52.

this will save a complete rear cylinder tear down. it would be required to replace the head gasket and cylinder gasket just to get a look at the rear cam. i dont want to disturb the rear cylinder if i dont need to
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Thu Oct 10, 2013 11:08 pm    Post subject: Reply with quote

im just saying make sure the seat didnt move before doing all that work installing new parts only to have the problem still exist. yeah, its probably the valve but i always like to be absolute. been bit in the ass too many times.
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It seems we can look at our magical Balls and come up with a fix?

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Greg Riddle
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PostPosted: Thu Oct 10, 2013 11:32 pm    Post subject: Reply with quote

got it
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