low compression after rebuild- noise - bent valve?

[natemoen]

As has been stated, bent valve means it can't close which would give you zero for compression.

You have to remember that this is rough metal to rough metal contact surface (with holes in it too!) The two surfaces over time smooth out and seal better against each other. YOU WILL HAVE low compression for awhile, that's how it works. I put new rings in over the winter and still havent checked compression.

The majority of the seating of the rings happens in the first 50 or so miles but even with that it isn't done till more like 1000 miles. So I would say get it together and get her broken in. Have you ever broken an engine in?

[DGXSER]

Honestly I think your just a bit nervous having just put that mush time and energy into your first rebuild. From the readings your seeing, I am certain you have no valves bent, and the numbers did not shoot up enough to say you have nay major ring issues. They just need to be seated in good with the hone on the cylinder.

Button that lady up and break her in right. Never broke in a motorcycle engine, so I will not offer any words of wisdom on it, but typically you want to vary your revs wihtin a reasonable range and change the oil after the first few hundred miles.

[KA1J]

If you had a bent valve, your compression on that cylinder would be zero. Looks like you got lucky.

Phil, My cut & paste to save typing the same thing over again wasn't so good. That was supposed to read cyl 1, 2, 3 & 4

Corrected it should read...

Cyl 1: 90 dry - 100 after adding oil to the chamber

Cyl 2: 88 dry - 90 after adding oil to the chamber

Cyl 3: 93 dry - 115 after adding oil to the chamber

Cyl 4: 90 dry - 115 after adding oil to the chamber

So from what you said I take it none of the cylinders indicate a bent valve. If so, yes I am indeed lucky. I was trying so hard to do everything exactly right that it's taken a very long time to get this back to where I can button it up. Every time something happens that makes me undo & re-do reinforces how much I don't know, no matter how hard I try to catch it all...

I'm still surprised the compression is so low even though the walls are freshly honed & there are new rings in it. I expected higher numbers seeing as the carbs are not even on the bike and I wouldn't have expected the minute scorings from the honing to pass that much air. I was expecting the readings to be in the 120's-130's at this point...

Last time I was this far into an engine was in 1969...

Fingers crossed, this has been more convoluted than I expected.

[KA1J]

As has been stated, bent valve means it can't close which would give you zero for compression.

You have to remember that this is rough metal to rough metal contact surface (with holes in it too!) The two surfaces over time smooth out and seal better against each other. YOU WILL HAVE low compression for awhile, that's how it works. I put new rings in over the winter and still havent checked compression.

The majority of the seating of the rings happens in the first 50 or so miles but even with that it isn't done till more like 1000 miles. So I would say get it together and get her broken in. Have you ever broken an engine in?

Hi Nate,

Last night cylinder 1 had zero compression, wouldn't even budge the compression tester but the intake shim was way off. I followed the suggestion to use new shims so I bought the four I needed as new from the Kawasaki dealer (Yama was out & wanted $22 each to order them...) and I bought one from an independent shop). They did make a difference.

As to breaking in, I bought some inexpensive wet clutch oil at autozone when it was on sale for $2/quart. I figured I would change the oil & filter after 100 miles and then do the same at 500 miles. I'm not into high revs so I figured for the first 100 miles I'd drive it around the local area and let the larger wear particles peel off & get snagged in the filter. After that I figured some mixed interstate and backwoods roads would be good for the next 400 miles & then put in better oil & filter and change again at 1000 miles.

The last time I broke anything in was when I got married the first time & I haven't been the same since...

[cywelchjr]

Hi Nate,

Last night cylinder 1 had zero compression, wouldn't even budge the compression tester but the intake shim was way off. I followed the suggestion to use new shims so I bought the four I needed as new from the Kawasaki dealer (Yama was out & wanted $22 each to order them...) and I bought one from an independent shop). They did make a difference.

As to breaking in, I bought some inexpensive wet clutch oil at autozone when it was on sale for $2/quart. I figured I would change the oil & filter after 100 miles and then do the same at 500 miles. I'm not into high revs so I figured for the first 100 miles I'd drive it around the local area and let the larger wear particles peel off & get snagged in the filter. After that I figured some mixed interstate and backwoods roads would be good for the next 400 miles & then put in better oil & filter and change again at 1000 miles.

The last time I broke anything in was when I got married the first time & I haven't been the same since...

Hint here, many people break in engines incorrectly, by doing it the way the manufacturer says, which is based on making sure that you don't stress anything rather than making sure that things seat the way they really should for best life. As well, most motorcycle manufacturers actually do this break in run for us on new bikes now at the factory before they load them into the box for shipping. At least on the higher end machines, as they do the several WOT runs on a chassis dyno right off the assembly line floor. Here is the link to how to break in a newly built engine the right way, and and explanation of how it works.

http://www.mototuneusa.com/break_in_secrets.htm

This is well worth a good read, and this guy shows the results with parts taken from engines broken in this way.

[natemoen]

Ah Cy got to it first. Even if you just do that at the beginning and then take it easy after you will be better off. The hard engine breaking really is a big part of it

[cywelchjr]

Yep, as the article states, both parts are important, it's the high pressures of the hard acceleration that pushes the rings hard against the cylinder walls so they get filed and sealed against the walls before the roughness of the hone wears off (which is important) but the decel is also important as it pulls oil up there and washes the bits of metal off and into the pan where the oil filter can pick them up so you get rid of them.

Basically as it says, one good session and then just ride it normally but remember to vary your speed for the first 500-1000 miles. And I think he says to change the oil after the first break in run, cause you WILL get lots of stuff in there.

[natemoen]

My oil was real sparkly from the metal shavings and dark when I changed it after the first 30 miles, after the next 100 miles it was still a little sparkly but looked like new oil coming out. Now the other night when I changed it, 4-500 miles or so, still looked like clean new oil but not much metal at all.

[LoHo]

Lots of folks have bent valves on these beasts, but I drove several miles (slowly and struggling) with the cam chain skipped two teeth without damage to the valves after an abortive attempt at cam chain tensioner swapping.

As for seating the valves after a rebuild, I can't remember if it was a discussion here or elsewhere, but IIRC the consensus was to push the bike hard from the start, so that they seat in the full throw of their bores. Don't baby it, as the seat will alter the ring geomentry if you get on it hard after seating the ring softly.

As with all of my advice, check elsewhere to make sure I'm not full of crap....

[James England]

When I changed my CCT to the Venture one, I also got the camchain skipped by one tooth. I got it all together (having removed the camshafts as I didn't fancy that DIY Pro-Motion tool thing)... but, when the slack was taken up, the cam dots weren't lined up properly. I almost hit the starter button but a little warning (which for once I heeded in time) said "turn the engine slowly with a wrench and trplie-check everything". I was surprised at how easily done it is to get things misaligned. With a bit of fiddling, I got it right eventually.

I doubt you have bent a valve. You have compression and, as has been said already, even a small amount of bend would result in zero compression immediately.

I personally would not get too sidetracked on compression readings. We used to just put a thumb over the plughole to check for compression!

[Rickrod3]

Plus 1 on the compression

90 psi is all you need to get the motor running. with a bent valve you will zero psi. At least thats what I had.
If you unstalled your rings properly and everything in spec; they seat and compression will improve.

Rick

[KA1J]

Well some good news today. I have the engine assembled, found 7 of the 8 round Allen nuts to bolt the headers to the engine (more coming early this week from fleabay), got the headers on (minus the right side heat shield that these headers came missing...), plugs in, inserted key, little squirt of starter fluid in each intake (carbs not in yet).

Ignition engaged &... Roar!

YES!

There is a God & I don't have a bent valve!

I still have much to complete for it to be ready but I'll be ready to run by next week. CyWelch offered this address & Natemoen concurred earlier in the thread http://www.mototuneusa.com/break_in_secrets.htm and I'll give this break in sequence a go. A big chunk o'me is of the old school that says break it in how you use it. That link goes some steps further as to what to do & I'll follow that break in format. I'll run it out to I-95 and do the sequences stated there. I'll do 50 miles or so & bring it back for an oil change and new filter.

I'll probably change my oil/filter more than suggested, I don't want those liberated bike bits floating around inside the engine. Fresh oil & new filter makes for a happy engine.

Autozone had a good deal for $2/quart a month ago & I bought all they had (15 quarts). Not sure what I'll use after that. Was using Amsoil but don't know if it's really worth the $ & possible starter issues I read about when using synthetic.

All in all, a much better & productive day than recent days working on the bike.