Compression problem rear cylinder
Thread Starter
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Cruiser
Joined: Aug 2008
Posts: 190
Likes: 25
From: Rotterdam, Netherlands
Absolutely! I thought I had to take the engine out before I would be able to
do anything. But the bike is a great workbench on its own
Mhh, ok. The outer looks of the engine begs to differ though. Its a blank aluminum engine that bears a few scars of time. Some bolts and nuts are pretty eroded, giving the impression it is still in original state, or the work has been done like 10 years ago.
No, piston and barrel are as new. The upper compression ring was broken in 2, the 2nd in 3 pieces. I was glad I filled the engine casing with cloth to prevent debris from falling into the casing when I would lift the cylinder, because thats exactly what would of happened.
As I told, in lower rev ranges when putting some strain on the engine, I thought to hear something resembling piston slap of one cylinder. Although the barrel itself does not show the signs of it, maybe it has something to do with breaking piston rings. Or a previous worker broke one during assembling, and the other one went of natural causes. Compression was good last year, but prolly only on one ring.
From all the things I've seen happening to engines this is the first one where piston rings were broken. I read about how air cooled engines put more strain to piston and rings because of inconsistent cooling, and this the first air cooled 4 stroke engine I opened up, so I learned something I guess
Last summer, I changes the default (or is it part of a stage one kit?) 0.45 pilot jet for a 0.48 one. When I bought the bike it was clearly running lean. Under constant speed, you could feel the bike holding back regularly, sometimes it missed a stroke when picking after coming out of a corner, and it suffered a lot from after-burning in exhaust. Maybe running lean for a long time paved the path for what I'm seeing now...
Another question;
Are the cylinders nicasil treated? Or is there is cast iron inner lining shrunk in?
do anything. But the bike is a great workbench on its own
No, piston and barrel are as new. The upper compression ring was broken in 2, the 2nd in 3 pieces. I was glad I filled the engine casing with cloth to prevent debris from falling into the casing when I would lift the cylinder, because thats exactly what would of happened.
As I told, in lower rev ranges when putting some strain on the engine, I thought to hear something resembling piston slap of one cylinder. Although the barrel itself does not show the signs of it, maybe it has something to do with breaking piston rings. Or a previous worker broke one during assembling, and the other one went of natural causes. Compression was good last year, but prolly only on one ring.
From all the things I've seen happening to engines this is the first one where piston rings were broken. I read about how air cooled engines put more strain to piston and rings because of inconsistent cooling, and this the first air cooled 4 stroke engine I opened up, so I learned something I guess
Last summer, I changes the default (or is it part of a stage one kit?) 0.45 pilot jet for a 0.48 one. When I bought the bike it was clearly running lean. Under constant speed, you could feel the bike holding back regularly, sometimes it missed a stroke when picking after coming out of a corner, and it suffered a lot from after-burning in exhaust. Maybe running lean for a long time paved the path for what I'm seeing now...
Another question;
Are the cylinders nicasil treated? Or is there is cast iron inner lining shrunk in?
Last edited by Daedalus; Jan 31, 2018 at 12:56 PM.
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,005
Likes: 7,540
From: Poolville
Well you obviously have aftermarket base gaskets so someone was in there before they probably rerung it and did not correctly set the ring end gaps that would cause a ring to break. I believe the top ring is right around .018" ring end Gap and second ring is right around .022"
Last edited by 98hotrodfatboy; Jan 31, 2018 at 03:25 PM.
Intermediate
Joined: Nov 2017
Posts: 36
Likes: 3
From: North Las Vegas, NV
I found it to be something of a PITA removing the allen head bolts on the top cover. When I put mine back together, I swapped them for stainless hex head bolts with enough washers for the bolt head to clear the top cover. I had to tear mine back apart after finding a head gasket leak and two times messing with the darn allen heads was enough for me.
Thread Starter
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Cruiser
Joined: Aug 2008
Posts: 190
Likes: 25
From: Rotterdam, Netherlands
I found it to be something of a PITA removing the allen head bolts on the top cover. When I put mine back together, I swapped them for stainless hex head bolts with enough washers for the bolt head to clear the top cover. I had to tear mine back apart after finding a head gasket leak and two times messing with the darn allen heads was enough for me.
Indeed, I'll try to get something else than the allen ones I removed when I put her back together again. I'll try, because on this side of the pond none metric stuff is hard to come by 
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,005
Likes: 7,540
From: Poolville
https://ads.midwayusa.com/product/548161/chapman-model-2307-8-piece-metric-hex-bit-set?utm_medium=shopping&utm_source=google&utm_camp aign=Gunsmithing+-+Tools%2C+Jigs+%26+Fixtures&utm_content=548161&cm_ mmc=pf_ci_google-_-Gunsmithing+-+Tools%2C+Jigs+%26+Fixtures-_-Chapman-_-548161&gclid=CjwKCAiAksvTBRBFEiwADSBZfFMKGQe3RfBVO LE3K0l7bwhaKCTX0lmn3l_fpb82wpTcZfD-HY803RoCLqMQAvD_BwE
you might need to open the link in a new tab to view it...
Last edited by 98hotrodfatboy; Feb 1, 2018 at 06:03 PM.
Grand HDF Member
Joined: Apr 2007
Posts: 3,712
Likes: 3,030
From: Brighton, MI
Nice looking Dyna! Just a little heads up, do a little reading about stripped head bolts. Not saying you have that problem, just mentioning it so you can be aware/watch for it.
Glad you found the disassembly straight forward...I am still running original gaskets and the rear is weeping. I keep putting off the repair. YD
Glad you found the disassembly straight forward...I am still running original gaskets and the rear is weeping. I keep putting off the repair. YD
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Thread Starter
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Cruiser
Joined: Aug 2008
Posts: 190
Likes: 25
From: Rotterdam, Netherlands
So, after a tough winter, I think I sorted things out
Rear cylinder piston broke both compression rings, and showed signs of eating itself away against the cylinder. Got my cylinders honed to the 1st oversized specs, got new pistons, got everything cleaned up and I'm ready to put things back together again.
One question, who invented the oil scraping rings? Are these buggers ment to fit that tight? I got the first piston in the cylinder, and I've put many pistons into cylinders, but this is the first one where I needed a drink afterwards... Do these oils scrapers really fit that tight?
Cylinders are on spec, according to the slot clearance of the compression rings, but the construction of these oil scrapers (with the slotted spacers and rings) really make it hard to assemble things. Is this normal?
I think I know why these oil scraping assemblies are hard to compress, because the scraping rings lean against the slotted spacer ring, and you can only compress the spacer by compressing the scrapers (I really hope I make sense). The piston moves up and down the cylinder and can be rotated in its rings, but assembling this one felt... awkward.
Rear cylinder piston broke both compression rings, and showed signs of eating itself away against the cylinder. Got my cylinders honed to the 1st oversized specs, got new pistons, got everything cleaned up and I'm ready to put things back together again.
One question, who invented the oil scraping rings? Are these buggers ment to fit that tight? I got the first piston in the cylinder, and I've put many pistons into cylinders, but this is the first one where I needed a drink afterwards... Do these oils scrapers really fit that tight?
Cylinders are on spec, according to the slot clearance of the compression rings, but the construction of these oil scrapers (with the slotted spacers and rings) really make it hard to assemble things. Is this normal?
I think I know why these oil scraping assemblies are hard to compress, because the scraping rings lean against the slotted spacer ring, and you can only compress the spacer by compressing the scrapers (I really hope I make sense). The piston moves up and down the cylinder and can be rotated in its rings, but assembling this one felt... awkward.
Last edited by Daedalus; May 1, 2018 at 01:26 PM.
Grand HDF Member
Joined: Apr 2007
Posts: 3,712
Likes: 3,030
From: Brighton, MI
If I understand you correctly, no, they should not be really tight. Each of the scraper rings should pivot independently of the spacer ring. The spacer goes on first, then the bottom scraper, then the top. Check out the vid below, as you can see, once installed it's very little effort to rotate them. Or are you just saying they are a pain in the **** to install?
It's for a twin cam but the install is the same as the evo. Again, it should not be tight but not loose either. YD
It's for a twin cam but the install is the same as the evo. Again, it should not be tight but not loose either. YD
Last edited by Yankee Dog; May 1, 2018 at 01:42 PM.