| Author | Message | ||
     Gp81 |
Just pulled the rear head.... Think I should have done this a long time ago. My engine experience has been limited to dirtbikes and such (single cylinder stuff) but I am pretty sure that there is not supposed to that much of a gap between the piston and the cylinder wall... opinions plz.....   | ||
| Hughlysses |
That's a lot of carbon, but that's about how my 2007 rear head looked when I tore it down after a crank failure. Are your rocker cover PCV valves still vented to the air box? There's no way you can eyeball the gap between the piston and the cylinder. Get a feeler gauge and check it. Is the wall scored? | ||
| Gp81 |
well I took some business cards of mine that mic'd out bout .015" and can get almost the whole cylinder lined between the piston clear down to the rings... haven't pulled the jugs yet to check for scoring... any ideas on a complete top end rebuild kit??? and that's an affirm on the vents to the air box | ||
| Gp81 |
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| Electraglider_1997 |
You need to ride in the rain more often and maybe that would help keep those parts cleaned of carbon. Just guessing on that though. | ||
| Sagehawk |
I am impressed! My 96 road king looked akin to that at 48000 miles. Its always ugly at first but cleans up good. Dont take that clearance to heart just yet. Measure cylinders when they are off, inline with crank and at 90° to crank, an inch down into cylinder and a inch or so up from bottom. Rough at that point. For good measurements, as tootal says, mount them in torque plates for actual good numbers. Measure pistons an inch or so up onto the skirts. If solid skirt, measure inline with pin and 90° to pin. I have seen some that the top land is smaller than skirt diameter and it appears to be to much clearance.good luck and hope its just mostly dirty with carbon. | ||
| Gp81 |
What is the actual allowable clearance??? with business card mic'd at approx. .015" and factoring for paper compression that would put me at roughly .025" - .030".... curious as to what the tolerance is? | ||
| Griffmeister |
There is no spec for piston to cylinder clearance. The cylinder is checked for wear using a torque plate. Multiple positions should be checked so as to determine taper, out of round and overall wear. Max allowable cylinder wear is 3.5008 in inside diameter. The piston is to be cleaned and checked for ring side clearance as well as wrist pin clearance. Other than that, if there is little to no wear/damage showing on the outside of the piston and the ring grooves and wrist pin are okay then the piston is good. Like Sagehawk said, although the manual doesn't say for sure, many pistons have a smaller diameter on the top land above the first compression ring so you should not use that to judge clearance. If there were a spec, you would still have to remove the rings, clean every surface and check the entire bore length with a torque plate installed. Just pulling the heads won't tell you much, just get you overly concerned. | ||
| Jstav2012 |
I hate to threadjack, but... That rear head looks like it has oil weeping at the rear of the head gasket. I noticed on my bike last night that it is similar. Mine runs fine, no discernible lack of power, or anything. Is this common, and any thoughts on just leaving it be? oil doesn't seem to accumulate, but just crusts up those two fins at the back. When I originally got the bike, it was missing one front exhaust stud, and the lower exhaust bracket mounting bolt. Could this have put extra stress on the rear head, and by fixing it, possibly resolved that leak? | ||
| Tootal |
As everybody is mentioning, pistons are measured a 1/2" to 1" from the bottom, 90 degrees to the wrist pin. That's pretty normal carbon for any engine. If the pistons are good and the bore is within spec with torque plates I'd ball hone them and rering the pistons if you want to save some money. If you want it the best it can be then have the cylinders measured and see how big of pistons you need to go oversize. You might get away with .005" over if they make them, otherwise .010" would be the way to go. Have the cylinders properly honed in torque plates by a good shop. Have a valve job done and put it back together. It will be quiet compared to factory. Also, if you change pistons then bead blast the old ones and weigh them and see if you can get the new ones to weigh the same otherwise you will not be balanced anymore and could induce some vibration. | ||
| Uly_man |
Is this the bike? "My 06 uly sat outside for the last year and a half while I was living in an apartment. it currently has 56,000+ miles on it and now that I have a new house with a garage and all my tools in one place figured it would be a good time to do some serious maintenance. Swapped fluids and filter, new plugs and wires, sprung for the rider comfort kit and installed that, new throttle cables and idle cable, new seat, new air filter ect". It seems odd that in two days, after doing all of that, you then dropped the engine and pulled the heads off. What was the problem with the engine? Unless it is another bike of course. That is not bad "carbon build up" just soot from a cold engine run. You can still see the numbers on the pistons "crown" and the shape on the face of the valve head. Did you do a cylinder compression test before this and what were the results? Advice? Well since you have the engine apart anyway. Take the cylinders to a pro to measure the bores spec and then do what they advise IE Rings, re-bore or whatever. Get the heads checked as well and change all the "engine in bike hard to get to" seals as well. And the oil pump gear upgrade while your at it. | ||
| Gp81 |
Yeah, same bike.... I need to readjust the throttle cables as the rpm's were hanging a bit on the decel... With some backfiring too.... Idled well so I thought that there might be some clogged injectors and/or carbon debri in the valves.... So brought the rpm's to 3000 and held it for about 30-45 seconds as that's a normal cruising speed and all was well until "BANG" Backfired so hard it killed the motor.... That was a first for me so I pulled the heads and am looking at the very least a top end rebuild.... | ||
| Gp81 |
Ok, so discovered upon removal of the jugs that ALL 3 rings on both pistons had magically alligned to the front of the engine..... Maybe that was the problem??? | ||
| Uly_man |
Would it not re start. | ||
| Gp81 |
Didn't take the chance.... And now I am curious as the the piston ring alignment issue that I discovered.... Btw.... On the backfiring I could see the explosion around the throttle plate | ||
| Sagehawk |
Backfired back thru intake? Perhaps a chunk of that carbon turned loose with motor at that rpm and unloaded. Road king was on dyno at galveston rally years back, 3 pulls. Rev limiter at 6200 rpm. Last pull, peak horsepower showing round 5900. Hit rev limiter as operator didnt get out of it quick enough. When motor slowed and relit, it blew a chunk of carbon. You shoulda seen the black cloud out of that white brothers pipe when that crap hit those discs. Kinda funny, but i knew then that upper end would have to be redone to clean it out. Still rode it rest of summer to get to winter. | ||
| Brother_in_buells |
}Ok, so discovered upon removal of the jugs that ALL 3 rings on both pistons had magically alligned to the front of the engine..... Maybe that was the problem??? looking at the fourth pic in this post got me some ??? to! http://www.badweatherbikers.com/buell/messages/476 23/738037.html?1400643104 | ||
| Gp81 |
So looking very closely at the jugs and at 51,000+ miles the ONLY marks I see are faintly the cross-hatch hone marks.... Somehow the piston rings had all magically aligned to the front of the engine..... Am I correct in assuming that this is the cause of high oil consumption ( recently noticed black smoke out of the drummer can) and a possible cause of the backfiring issue ( crank case pressure build up) and just go with new rings and cometek gaskets and reassemble??? | ||
| Tootal |
Well it wasn't helping anything but you really need to measure the bores while they are in torque plates. That's the only way to know for sure. The cylinder walls will change shape under torque and must be measured and machined while under torque. I will be honest with you, since you're already down this far go ahead and fix it right. You will be so much happier in the long run. If I were you I would go to the next size piston and have the bores properly machined for a perfect fit. This will stop your oil consumption and make the engine quieter and last a lot longer. You don't want to be doing this again in three years! If you can't afford that now I understand but if you possibly can by all means get it right now. |
