Another Boring question

ok, I checked out the archives and didn't quite get the answer to my question.

I have a 78 Z1R with the stock head and cams on a 76 900 bottom end and block that's been bored to 1045. Stock coils and points too. Upgrade to that soon.

After many unsuccessful attempts to get it running smoothly, I checked the compression and its all over the place. I checked the valve clearances and they're spot-on.

I get 157, 160, 144, 170psi left to right. I hooked up my compression tester hose (withOUT check valve) to my compressor and did a leakdown test by ear. Valves are not leaking as far as I can tell. I squirted 3 shots of oil into each cylinder and consistently got 190-195 psi.

I have several questions;

Are these differences between cylinders significant? It seems like it to me, especially #3. Percentage-wise they are farther apart than the service manual says is acceptable.

If I have to bore to the next step, is a 1075 10.25CR setup the way to go? Or for the same $$ go with a 1105 10.25CR. It sounds like some people are pretty condervative on that topic. I'm planning on getting a better ignition and I'm running Mik 29's.

Should I resleeve the 900 block or buy a used 1000 block and bore the sleeves that are already in it?

If I get a 1000 block, what needs to be done to put it on 900 cases? I didn't do anything to get the 1000 head on the 900 block. Is that right?

Redline looks like a good choice to do the work, is there anyone else to recommend closer to the west coast?

Thanks

Lots of questions... hmmmm... to recap, your bike doesn't run right. You mention it doesn't run smoothly. That is the ONLY symptom of a problem other than the compression numbers you note.

What does "not run smoothly" mean? Does the bike vibrate? Does it lurch? Does it have poor acceleration? Please describe the problem that led you to make the compression measurements.

As far as your compression goes, I think you already have ideas on what you want to do. If the bike were mine and my compression varied that much across the board, I would pull the head and block off and measure the piston diameter per your shop manual and measure the cylinder bore (3 places) per your shop manual. I suspect that with the compression as HIGH as it is but uneven, you had ring seating issues when the pistons were first run in. I also suspect, you can hone the cylinders and put in some new rings and get compression a bit more consistant without reboring.

Before jumping into a rebuild, please amplify your "not running smoothly" comments as this well could be a funciton of some other problem not related to the compression disparities.

Well, maybe I jumped ahead in the natural sequence of diagnostics...

I do need a new ignition setup, (I'm saving the $$ for elect) one set of points are pitted pretty bad, stock coils. The bike runs rich, black sooty plugs. I suspect this is mostly due to the weak ign. since the carbs are jetted close to stock. Since I can't afford the ign right now, I started checking other things out; carb synch (ok), valve adj(ok), compression.

As far as the bike runs, when it's idling, or especially when riding it at low speeds, cruising through town at partial throttle it lurches, bucks and snorts. When you get on the gas, it seems to run really good as far as I can tell.

The ring seating that you suggest knocked something loose in my brain... In a post some time ago, maybe in the archives, someone said never to run a new engine on synthetic oil for ring seating issues. This is exactly what I did when I built the engine some time ago. At that time, I couldn't find any new rings to fit the 1045 pistons. It seems like I couldn't find the proper thickness. I honed the cylinders and ran what I had. The clearances then were good and the engine doesn't have a lot of miles on it.

Can I change the oil and get them to set better, (maybe shoot some carb cleaner in the cylinders and change oil twice to flush) or would I have to pull the block, re-hone lightly and run std oil?

Thanks,

I would not shoot carb cleaner into the cylinders for sure. I WOULD keep my eye on eBay and buy an electronic ignition from another bike. If it is related to your bike and you can score the entire igntion as a whole (pickup coils, coils, igniter and resistor bridge) you should be able to get the igntion sorted out in short order. In addition, check the voltage going to your coils now using a multimeter. Check after turning on key but before starting. The voltage at each coil should be ~ 12.4 VDC.

I've definitely been looking around for ignition setups, just need to roust the $$ before I bid.

I ran across your archive for powering the coils via a relay to the batt. That seems like a good idea whether I get a new ign or not, so I'll try that too.

Any thoughts on getting the rings to seat better, assuming that's the problem?

Thanks again for the tips.

I did the coil upgrade to my 1000 and man what a diff. Are u absolutely sure your valve clearance is not too tight on all your cylinders? If u only have a couple thuo on one and say4 on another, the compression will be all over the place. To be specific, I had about .001 on two cyl. and and .004 on the other two and the difference was 35lbs.

Post edited by: nads.com, at: 2005/10/17 21:02

Looking forward to the ignition upgrade. I bought all the stuff at the parts store on the way home today. If my plugs run brown... hoooo-weeee... you might hear me whup-and-holler all the way over here on the left coast.

Pretty sure about the valve clearance, intakes were all .002"-.003" Exhausts were all .003-.004".

If the cylinders with the lowest compression have only .002 clearance, you might try making them .004 in an attempt to shed light on the pressure differential problem between cylinders.

nads.com is addressing the compression issue I didn't really get into. The ragged running sounds ignition but the compression issue will still be there. Did you measure valve clearances?

The 1045 really made the 900 sleeves too thin, and they had problems staying round. 1105cc 1000s have the same problem. We try to talk people out of those kits.

You can resleeve and do a fresh 1015 and it will make more power than an out of round 1045.

A 1000 block and a 1075 is an option, but the block is not a simple drop on to the 900 cases.

If you want to go to the trouble of splitting the cases and boring the top case, go with a 1200. It would be the same money as a smaller motor.

Call us if we can help.

Jay
www.kzzone.com

Thanks! Awesome info. I just listed a bunch of stuff on ebay, so I might be interested in the 1015 option as soon as the $$$ starts rolling in!

Sorry for jumping in here but I have a question for ya Jay.I have 1000 cases,for me to run the 1200 kit do I need to have the top case bored?And how will the streetability be with this kit?