Compression increased by more than 50 lbs??????

[nuke em]

I had an interesting thing happen from last weekends trip to Walden dunes with Dennis(fl670r) and Jerry(Drakman). Ok, I went ahead and reinstalled that beat to death piston in the 420. I removed most of the ceramic coating along the outer edges, all the teflon coat that was left, put fresh grooves/scratches around the skirt with 120 grit sand paper to help the oil cling to now that the Teflon is gone, cleaned the piston ring grooves back up to spec, then re installed the rings exactly the way I took them off. I did NOT hone the bore because I figured they would be riding in the exact same spots with the exact same rings. I checked the compression before I left, 92-94lbs. Thats about where it was after the Killpecker ride. Damn, hope it holds up long enough for several hours of riding, not to mention I will be going 2,500ft higher up to ride.

I installed the huge 26" tires and the clutch with the "Heel Clicker cams".  It was absolutly boggy/rich all thru the power band. The cams/spring combo didn't allow it to get into the power band at all. I didn't bring the puller so I couldn't adjust it. Dennis had smaller jets and 20" sand shark paddles to loan and Jerry offered his new top of the line buggy stand...thanks guys. I jetted down 8 sizes and 2 clip positions before I could pin the throttle without blubbering. I couldn't adjust the clutch so I could never get her in the power band, sooooo, I just rode it like that(10 or so hours total). I am not sure but don't think I ever broke 6500-7000 RPMs.

Anyway, as I was leaving I checked the compression, 130-135!!!! Damn, what happened? I thought maybe it never really seated at KP? I checked it again today here at 6,000ft... 145LBS!!! WOOHOOO. I put the good clutch back on and the 22" Spider Tracks, she is faster than it was before Killpecker. Maybe leaner now with the changed jetting? Nope, plug looks pefect, dark chocolate.

Why did the compression raise? Was the teflon effecting ring seating during break in? Those brown blow by areas we spotted earlier caused by lack of ring seating? I still need a new piston soon, there was 20-30 thousandths gap near the mid skirt areas. Confused but happy!

 Just thought you guys may want to know. Guys, any ideas on what may have caused this?

Gary

[ludedude]

Here's my $0.02

I've used the teflon and ceramic pistons before (think Vic and Richard have too??) with fine results.....they came from Bore-Tech....difference there???

I fail to see how piston coatings would affect compression as the piston doesn't touch the cylinder...it's the rings to cylinder that creates the compression, right...so....see my thinking....then again I just got up  :roll: LOL

[PilotSniper]

Here's my $0.02

I've used the teflon and ceramic pistons before (think Vic and Richard have too??) with fine results.....they came from Bore-Tech....difference there???

I fail to see how piston coatings would affect compression as the piston doesn't touch the cylinder...it's the rings to cylinder that creates the compression, right...so....see my thinking....then again I just got up  :roll: LOL

I don't have any money right now (no cents  :wink: ), but Lude's correct in his assumption, in my opinion. Maybe it had something to do with the Bore-Tech process on the cylinder walls working in conjunction with the moly coating on the piston skirt? I don't know, but I'm a believer in the Bore-Tech process, no matter what anyone says.

[nuke em]

You are exactly right, the piston walls should be riding on a thin film of oil, but my piston has been touching the walls in certain areas because of an improperly balanced piston(which I caused by removing about 3/8" from bottom of the skirt to make it fit). Thats why the piston is way out of round now, its been slapping the wall some. The thrust angles on the short 350 rod is not helping things either.

My "other" theory is I didn't have suffecient load against the engine to really seat the rings. The clutch setup being wrong and huge tires put alot of load on the engine and rings. That may have caused alot more pressure and helped them fully seat. Maybe that made the difference.

I am looking at a CR500 rod and (89MM)piston now. If the lower rod will fit on the 350 crank, it will be a go! Just will need longer base studs and a spacer plate. A clean fresh bore, no balance issues, longer rod may give more torque and less high RPM plus a few more CCs. That will help on the thrust angles too.


Gary

[nuke em]

Hey PilotSniper, I have heard nothing but good things about BoreTech. I guess I will have to try them soon. Prices were reasonable. Do you guys order the matched piston along with thier process or just have it lined then bored?

Thanks for being a sounding board for me. I was begining to think I was loosing my mind. LOL

Gary

[ludedude]

I've always either sent a piston to them, or have them order one, they bore and impregnate to match the piston. That's one thing I've meant to ask, out of curiousity...how deep does the impregnation go....is it good for that bore only...or IF you need to bore it out....is it all gone in one oversize?

[Moskito]

Hey PilotSniper, I have heard nothing but good things about BoreTech. I guess I will have to try them soon. Prices were reasonable. Do you guys order the matched piston along with thier process or just have it lined then bored?

You can go either way  - Send Bill the jug and have him order a piston - ask him to get OEM if he can, Wiseco if he can't.

Sometimes he comes up with good piston & ring prices, sometimes you may be abel to match/beat his price.  I'd call him first (513-625-8374) and ask what he'd prefer.

That's one thing I've meant to ask, out of curiousity...how deep does the impregnation go....is it good for that bore only...or IF you need to bore it out....is it all gone in one oversize?

It's all gone in one shot.

It only impregnates the liner a few tenths (.000X") - only good for that bore and then it's gone.

[Ozpilot]

It sounds like this next engine will be an absolute winner - the last one was mighty impressive and this one should do the same or better with more reliability.  It seems you really need that better rod angle.

I wasn't sure if you were saying the new rod will give a few more cc's or the whole new setup will give more cc's.  The rod won't change the stroke but have you figured out the capacity with the 89mm piston?

It's great to see this type of development/experimentation happening - to me, that's what is so great about all motorsports.

[PilotSniper]

Hey PilotSniper, I have heard nothing but good things about BoreTech. I guess I will have to try them soon. Prices were reasonable. Do you guys order the matched piston along with thier process or just have it lined then bored?

Thanks for being a sounding board for me. I was begining to think I was loosing my mind. LOL

Gary

Oops! It looks like I'm late to the party!!! :oops:

Gary, as you might imagine, you've got your believers and you've got your skeptics. I took Skeeter and Lude's advice and sent out my jug and head to Bill at Bore-Tech and was very pleased with the pricing, service and end result. Skeeter's recommendation was to get the piston skirt coated with that black moly coating, then get the piston dome, head dome and exhaust port coated with the ceramic coating. I also had the Carbide Bore process performed on the cylinder walls. In my case, Bill hooked me up with a Wiseco piston with all of the trimmings. Being the newbie that I was (and still am!), I detonated the crap out of a piston and I was able to reuse the jug with just a simple cleaning to get out all of the metal and aluminum shavings. I attribute this to the Carbide Bore process, so like I said, I am a believer!

Spend a little more and have Bill take care of you. It's like buying an insurance policy.

Best of luck to you!!!

[Moskito]

My "other" theory is I didn't have suffecient load against the engine to really seat the rings. The clutch setup wrong and huge tires put a lot of load on it. Maybe that makes a difference too.

I'm slow on the response here...   I hadn't completely read the posts from the start.

I would have to agree on your assessment - "other" theory.  It's the only thing that makes sense... - sort of what popped into my brain when I was reading.  Don't know if it's viable or not, but I'll argue for you!

Maybe you've discovered a new Secret Squirrel Ring Re-seating trick?  

Maybe it had something to do with the Bore-Tech process on the cylinder walls working in conjunction with the moly coating on the piston skirt? I don't know, but I'm a believer in the Bore-Tech process, no matter what anyone says.

This too may have merrit.  When Bill first started doing the stuff, he was getting too much carbide impregnated into the jugs and it would take a pretty long time to seat the rings.

The carbide bits look like tiny balls under a microscope - no sharp edges, so you can see how it would take a while to seat the rings.

Maybe he got a bit more of the stuff impregnated than usual?  Just thinking out loud...

[PilotSniper]

Gary,

If you want to see pics of the Bore-Tech processes after Bill sent everything back to me, go here:

--->My Pilot's Pics<---

...then, after you enter the site, go down on the list and click the link that says "Modifications". The 16th section down has all of the pics of the jug, head and piston. Click the thumbnails for larger images.

As far as the pricing is concerned, I honestly don't remember. I think the whole thing turned out to be around $250, piston included. Whatever it was, it was well worth the money.

Let me know if you need any more info from me. God knows I owe everyone here lots of community service hours for the times they've saved my butt!

Talk to you later,

Sniper