need suggestions- 426 smokes on cold start after new piston
Posted January 20, 2002 - 01:24 PM
Posted January 20, 2002 - 01:40 PM
Posted January 20, 2002 - 02:01 PM
Also ditto the recommendation for high octane fuel. I don't remember seeing any 13.5:1 engine being OK'd for pump fuel. Knock and ping can definitely put a hole in the top of your piston, not to mention other fun side effects.
Posted January 20, 2002 - 03:37 PM
Posted January 20, 2002 - 04:14 PM
1. What was the recommended piston to cylinder clearance from Wiseco ?
2. What did the piston mike across the skirt at the largest point ?
3. What did the cylinder mike, how much taper did it have and how far out of round was it ?
4. What color was the smoke ?
5. Why would you use a used cylinder with a new piston ?
6. How much ring gap did you have on each of your rings ?
7. Did you deburr all of your sharp corners and and deburr all oil holes on the piston ?
8. What was your total piston to cylinder clearance before assembly ?
9. And the most important question. Why would you run any oil in your fuel ?
This can cause severe cylinder and ring damage because of the added load on the rings at there seating points.
After you awnser these questions I can give you a good assesment of your problem, but here is a early hint.
If you have to much piston to cylinder clearance the piston will rock slightly until warm depending on the severity of the clearance, which in turn allows oil from under the piston to get by.
This is what we see on the CRF's because of the skirtless piston (rocking in the cylinder) all CRF's I've seen smoke until warm and the clearances close up allowing a good firm seal.
One more question.......Did you take your valves out and see how far they had sunk into the seat ?
Checking for a ridge on the sealing side of the valve.
P.S. These guy's are right about the race fuel.....you better get some.
[ January 20, 2002: Message edited by: jaybird67k ]
Posted January 20, 2002 - 04:53 PM
Your ridin' bud, Kurt
Posted January 20, 2002 - 04:59 PM
I was afraid one of you guru's would ask about the cylinder/piston tolerances. This I didn't check. I did check the top 2 ring gaps and they were good. I was told not to worry about the oil ring(s) was told hmmmm if I can remember... "just poke 'em in there". So I did. I am thinking along the lines of the piston being too loose in the cylinder, but I could be wrong. I have had valve seals go bad in Honda's and they behaved a little different, the bike tended to smoke immediately on start, not delay like mine is doing. The only thing that makes this such a mystery is the power, it is so much better than it was stock.
As for race gas, I was told before I did this by some of the guru's over at DRN (I know, drn is a cussword sorry) that I wouldn't have to run it since 12.5:1 is stock. I also had a report from another who was running this compression on pump gas. Anyway, that is no big deal, I will run race gas just don't have any on hand.
I might end up doing the Eric Gorr 97mm 440 kit thing, just thought I would try a short cut since I have a dealer who likes me and gets me parts cheap. Not that I have the money to throw around but this was a chance I thought I could take. Thanks again guys, I'll try my best to help you when I can...
Posted January 20, 2002 - 05:14 PM
jaybird- also, the smoke is gray, it is oil smoke. I did the bean oil thing at the recommendation of my dealer who is an old time mechanic who splits yam cases with a rubber hammer, presses them back together with a press and gets more time from them than anyone else I know. Actually he gave me a bottle of bendzall and said to try it for a tank or two.
I can live with this smoke for a minute or so, I just don't want this thing to sieze on the face of a jump. I'm still healing from a bad wreck at the dunes two weeks ago and I'm too old for another any time soon...
Posted January 21, 2002 - 04:58 AM
Posted January 21, 2002 - 01:08 PM
Posted January 21, 2002 - 04:14 PM
Posted January 21, 2002 - 07:29 PM
Blue or gray smoke is obviously the cause of oil burning in the combustion chamber.
It takes a very small amount of oil to result in what seems like a lot of smoke.
In most cases, as SireThump as noted, such symptoms would conclude one to assume the valve seals.
This could be a coincidence, unless one of the valves got bent before, during or after your piston install.
However, I am more suspicious that your problem is with your oil ring. Mainly in that you had to force the ring into place.
Piston ring clearance is a critical spec in engine building. Your third ring, which controls oil flow, should freely move in and out of the groove. If not, excess oil would flow by.
Perhaps, due to heat, the ring is freeing itself after the engine heats up. Before then, obviously, too much flow.
Proper piston install also involves a precise match to bore and piston size. Simply purchasing a piston to size and installing it is sure trouble.
In all cases, the cylinder should be bored to match the new piston. Therefore a new piston into a stock cylinder should be .040 to .060 over.
Many pistons and cylinders wear together. After so many hours of use, the piston and cylinder usually get a bit on the oval side.
Therefore the new piston is forced into a hole that is tight on two sides, and lose on the other two.
Lastly, all new pistons are not made to the same exact size. Usually, good bore jobs are not spec’d to anything but a measurement of the new piston itself.
In multi cylinder engines, this means matching exact piston size to each cylinder bore.
At this stage, you may now have a damaged piston and cylinder. If you put a factory size piston into a worn cylinder, I would toss the piston, go with an oversized one, and re-bore. And of course, machine the piston to the necessary ring clearance spec. Not to say you can’t save this one, but it's a matter of doing a job correctly.
I don't think most piston manufactures ever ship rings that are matched perfectly for each piston. If anything, they provide you with extra material to remove for a proper match.
Just my two bits, so I hope there are some other engine builders on this sight with a little more of a modern view on this process.
[ January 22, 2002: Message edited by: DaveJ ]
Posted January 22, 2002 - 01:46 PM
a) having the cylinder bored / plated using the new piston for dimensional reference
checking end gap by inserting ring( s ) alone into cylinder and filing / deburring ends
c) putting same rings into their respective grooves and again verifying end gap? ( If inserted into cylinder that I guess a wire guage would have to be used, If no room that eyeballing? )
Steps a and b are obvious but never even considered step c if that is what you imply.
Please share more with us. We ( myself actually )obviously need your help!
Mike O.K. Thanks for the head's up! Hope your rebuild goes well. As usual my advise is : Please work patiently! ( This is advise I like dispence but sometimes have trouble putting into practice myself ! )
Posted January 22, 2002 - 02:07 PM
Also the main reason I re-built anyway was the fact that my hole-shots were getting worse and worse, and it felt to me like my bike wasn't making near as much power as when it was new. I can tell you that even with the smoking problem this bike has considerable more power now than before the re-build, probably more than when it was new but that's really hard to say since so much time has past. Thanks again guys and I'm out to the shop in a but to put it back together for one more try. Working 10 hour days this week has sure put a damper on my fun. And Hugh- patience is something I wasn't born with but as I get older it seems to get easier, and I really enjoy all this tinkering anyway...
Posted January 22, 2002 - 05:45 PM
Yes to A. Good machine shops will always ask for the piston in which the bore job is being done for. And yes, they should match one to the other.
A bore job, or at least a measurement for size and shape followed by a hone, should always be done before a new piston is installed, (unless of course there are ceramics involved).
In some cases, a process called "decking" is also performed, so to assure that any post assembly distortion is considered in the bore set.
This means applying the same pressure to the cylinder as applied when the engine is fully assembled before the bore job is performed. This is done because some engine designs will distort a perfect bore when assembled.
I doubt many shops would do this on such an engine, nor is is really that necessary in single cylinder apps.
As for B and C, it's a little more complicated.
Most piston designs have a spec for two ring settings. The first is the gap between the ring and the piston. In other words, the excess space between ring grove size and width of the ring. This means the ring moves up and down in the grove when the piston goes up and down, and also assurs that the ring can move freely.
The other setting is as you mentioned, assuring that the ring ends have a proper gap in accordance to cylinder diameter (I kind of left that out). This is where most people will push the ring in the cylinder using the head of the piston.
Pistons and rings come from the manufactures as do all engine componets - in need of special attention in order for the job to be done correctly.
Based on what Mike reported during his assembly process and testing, I really think he needs to start over when the time allows.
Unless, of course, he simply still has some of that bean oil in there.
Posted January 23, 2002 - 05:34 AM
Posted January 23, 2002 - 08:31 AM
You can purchase or sometimes rent a piston ring compressor. Well worth the money.
And I also forgot to mention that the gap between each ring is usually positioned at even increments. I think some pistons have positioning pins in them for this.
Talk with you guys later!
Posted January 23, 2002 - 04:15 PM
Posted January 24, 2002 - 03:58 PM
Just some food for thought.
There is no magic to building these single cylinder engines as long as the necassary parts are all checked to be within tolerance.
I've built a bunch of engines in my short time on this earth and am just fortunate enough to be a Machinist so all the sizing and stuff comes second nature to me.
I never trust any part that is sent to me and I check it regardless if its OEM or whoever.
As you have probably found out it is a no no to put a new piston in a used bore, I do all my on boring because I trust myself more than I trust other people to do it.
I use a place called US Chrome to do all my plating for me after I bore my cylinders.
The standard practice for boring a plated cylinder is this......Piston size at its largest point(across the skirt) + Reccomended clearance + .007 thousands = bore size.
So lets say for grins and giggles your piston was 4.000" and the reccomended piston to cylinder clearance was .002", then you would have 4.002", then add .007 to that you would have to bore your cylinder to 4.009".
This is the same for all bore sizes that we deal with on these bikes.
If you look at the numbers you will notice that the cylinder has been bored .009 thousands bigger than the piston but only .007 thousands bigger than the finish bore which would end up at 4.002"
This is because the guys doing the plating are looking to get .0035" thousands a side for plating thickness.
It is cheaper to buy a OEM cylinder as it is to
have someone bore and plate one for you, an OEM cylinder is about $200 and to have one plated is around $160 plus $50 for boring.
You can have a stock worn cylinder with a new piston sent to US Chrome and they will chemically strip the plating and replate and diamond hone it to fit the new piston.
I personally see no reason to go oversize on the bore with the OEM ones being so cheap, unless you just need more power or you have nothing else to do.
I have my old cylinder from my 01 426 that I will bore and plate to fit an oversize piston and keep just incase I want to dump it in a year from now just for fun. Or sell it to someone looking for one.
I hope this helps you understand the boring and plating process a little better, If not let me know and I'll try to help.
Posted January 24, 2002 - 04:29 PM
As far as pins in the piston to keep the rings in specific places, I've only seen this on 2-strokes to keep the ends of the rings out of the ports.
Thanks of the great explination on boreing, that was very informative!! I always thought that with the plated cylinders that the piston would wear out much faster than the cylinder and therefore the cylinder was frequently reuseable with new pistons because it wasn't yet out of spec. Does this not happen very often in real life?
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