Did another Compression Test

[TeamRealtreeHD]

Well, I did another compression test today. Last one was July 23rd, and since then, I put 15-20 hours on the bike. It has about 20-22 hours total on top end rebuild.

 

Last test on July 23rd:

Left cylinder: 184 PSI

Right cylinder: 185 PSI

 

Today after about 15-20 hours on it since last test:

Left cylinder 187 PSI

Right cylinder: 190 PSI

 

The first test I may have stopped kicking a tad early, today I kept going until I knew for a fact it stopped climbing for good. But I am pleased it didn't go down.

 

With around 190 PSI, when do I rebuild it... at what PSI?

[C&B]

Ur rings have seeded, its all good! Ride te hell out of it!! If you get more of a 10% diff between cyls, then tear down and re-ring or rebuild, whatever it needs.

[TeamRealtreeHD]

Ur rings have seeded, its all good! Ride te hell out of it!! If you get more of a 10% diff between cyls, then tear down and re-ring or rebuild, whatever it needs.

 

That is good to hear... it is running fantastic. I talked with a few guys I know on here, and they believe my pilot may be too high as my plugs are wet. But I can drop a size, down to 48's. That should clear it up. The top end pulls like a raped Indian, so my mains are good. The plugs look good inside with a caramel color, but the threads and stuff are wet. I pull them when I get home and it is after putting it through a small development.

 

I appreciate the advice on the 10% difference in cylinder PSI... but with this motor, and that high of compression, when will you know it is time for a rebuild on the top end? I know stock is like 110-100 is getting low. But what about this bike?

 

I can just ask Kevin, he built her up and knows. I just never got around to it. But just curious what you guys may have thought. That is great advice though on the rings. I owned 2 strokes but never a twin cylinder bike, so that is good to know.

[blowit]

Waiting until the compression drops off for a top end inspection is asking for disaster. We generally direct people to run 50-75hrs on a top end but IGNORE the compression for telling you when it is time. That is only a bench mark because your pistons are not supported like a thumper so the piston can wear out and NOT show in a comp test. I have seen a BUNCH and engines that were hanging on my a thread but showed good compression. Go by hours or time, location of riding, type of riding, and pay attention to your engine sounds and power.

 

You will save your self head aches in the end.

 

 

Brandon

[TeamRealtreeHD]

Waiting until the compression drops off for a top end inspection is asking for disaster. We generally direct people to run 50-75hrs on a top end but IGNORE the compression for telling you when it is time. That is only a bench mark because your pistons are not supported like a thumper so the piston can wear out and NOT show in a comp test. I have seen a BUNCH and engines that were hanging on my a thread but showed good compression. Go by hours or time, location of riding, type of riding, and pay attention to your engine sounds and power.

 

You will save your self head aches in the end.

 

 

Brandon

 

I know, and I appreciate the info... but I just wanted to get a general feel for the number. Like what is low for a motor like this one. That's all, not getting mechanical here, just talking numbers... plain and simple.

 

I do appreciate that though, as I agree too with what you said. I have seen on my 250r a few years back the piston was completely shot, it was.... and the compression read pretty good #'s. I had alot of work into that motor, it had compression well into the 200 PSI range, around 210 I believe on a fresh rebuild. But it was funny that you mentioned that, because I tore it down the one time to replace rings only to find the piston shot. But the compression reading was good.

 

But for my banshee, and the motor I have, I was just looking for a PSI # that would be considered low.

[blowit]

As a general rule, we use 10% max as cause to open one up. So a motor that pumped 200psi new would need looked at at 180psi. Personally, I rarely let them get that low before looking into because when compression starts dropping, there is definitely a reason. Most of our motors will hold near new comp right up until rebuild time and the rings are always shot.

 

Keep a log of your ride time and open it sooner than later the first time and that will give you a feel for how long the motor can go between rebuilds. If you stay on top of it, you throw rings and maybe pistons at it with a hone and run it for many years. If you wait, you WILL pay.

 

 

 

Brandon

[TeamRealtreeHD]

I wrote down the first compression date, then today, and how many hours in between. I will give it another compression test in 2 weeks before I put it away for the winter... than write down aprrox. total hours on it.

 

I will tear off the head and vylinders over the winter when I powdercoat the frame. If they needs rings, I will replace them. If they don't, I will replace them anyways. I want this top end to last through next summer as well.

[C&B]

I wasnt telling him to rely on the comp test for a rebuild. I do a comp test every 25 hours, if its dropped 10lbs, I pull the head and check shit out. Brandon is right about the feel of the motor, if you think anything at all has started to go away, pull the head. Cheap insurance. Sorry I wasnt clearer about the comp test. And Ive ridden mine for 40 more hours after a comp test, trying to fry it so I could go bigger and badder, so the ole lady wouldnt be pissed.. lol