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Author Topic: Cylinder wear and compression  (Read 189 times)

Dhastings1954

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Cylinder wear and compression
« on: May 16, 2015, 07:29:56 AM »
I am replacing the head on my 1998 Bullet 500. Long story. What concerns me now is the compression. I am told that if the bike has good compression you should be able to stand on the kick starter without having it go down. I had nothing like that for compression. I could easily push the kick starter to the start position without using the decompressor valve.
I have the head off and have looked at the bore. It does not look too bad, but the are vertical lines or scratches in several places. I am going to pull the barrel out and look at the piston too.
By way if history, my oil pump failed and the head was not getting oil. That wore out the rocker blocks. I repaired the oil pump, replaced the rocker blocks, and put in new oil lines and upgraded banjo bolts. In that process I stripped several threads and decided to replace head.
Now that I have it apart, I am trying to figure out if I should replace barrel and piston.
Any thoughts or advice?
Thanks
Duncan
Does it sound like
Vt Bullet

Hondo

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Re: Cylinder wear and compression
« Reply #1 on: May 16, 2015, 09:17:55 AM »
How about a little more info?  Is the motor stock or does it have any upgrades?  How many miles on it?  There are several weak point on these bikes that are often the topic of discussion.  Bottom end bearings, con-rod, piston, and valve train to name a few. With upgrades ranging from mild to wild reliability and performance can both be improved.  The big questions being what do I out of the bike in the end and how much can I afford.  I am currently in the middle of a clubman build with the goal of being to conduct short trips at highways speeds and long term durabilty for country cruising.  Do a search for the clubman build and bottom end work and you should find plenty to read.

Dhastings1954

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Re: Cylinder wear and compression
« Reply #2 on: May 16, 2015, 09:49:27 AM »
I bought it used, but I think the  odometer is accurate. 3364 miles. Took the barrel and piston out. The barrel has little grooves or scratches up and down or vertical. You can feel them with your fingers. The piston has abrasions in  similar locations to grooves in cylinder, 2 each on front and back. Probably at app 40 degrees and 130 degrees, if the piston wrist pin is 0 and 180 degrees. Same locations on front and back of piston. I am guessing I need to replace piston and barrel.
I assume this is all original stock barrel and piston. I am okay with replacing with stock, but should I consider the 535 cc barrel and piston kit?  Will that upgrade work with my stock head?
Advice appreciated.
Vt Bullet

High On Octane

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Re: Cylinder wear and compression
« Reply #3 on: May 16, 2015, 09:55:11 AM »
I bought it used, but I think the  odometer is accurate. 3364 miles. Took the barrel and piston out. The barrel has little grooves or scratches up and down or vertical. You can feel them with your fingers. The piston has abrasions in  similar locations to grooves in cylinder, 2 each on front and back. Probably at app 40 degrees and 130 degrees, if the piston wrist pin is 0 and 180 degrees. Same locations on front and back of piston. I am guessing I need to replace piston and barrel.
I assume this is all original stock barrel and piston. I am okay with replacing with stock, but should I consider the 535 cc barrel and piston kit?  Will that upgrade work with my stock head?
Advice appreciated.

If the cylinder and piston are both scored so badly that you can feel the scores with your fingernails, then the piston should be replaced and the cylinder over-bored.  The scoring in the cylinder will need to be bored until they are gone.  I would recommend taking the cylinder and piston to a machine shop to see how deep the scoring is and what size over-bore piston you will need for rebuilding.
Scottie J  ~  Bulldog Kustoms Denver  ~  1958 Enfield/Indian Trailblazer - The Blackhawk

cafeman

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Re: Cylinder wear and compression
« Reply #4 on: May 16, 2015, 10:53:54 AM »
Funds permitting, at the least a new oversized piston and  boring would be in order. I like the idea of reboring in increments and getting mileage from a cylinder vs. boring out from standard right away to do the 535. Unfortunately piston choice is limited but the ones available make it possible. I know Ace offers a nice piston but only in the big bore 535 size if I'm correct. If incremental over sizes were offered that would be ideal. :)
Current Fleet: 2001 Royal Enfield Bullet 500 Cafe Racer
                     1996 Yamaha Seca II
                     1991 Husqvarna 350WXE
                     1991 KTM 250MX
                     2004 Husqvarna TC450

ace.cafe

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Re: Cylinder wear and compression
« Reply #5 on: May 16, 2015, 11:25:20 AM »
We have a couple 86mm Ace pistons left over from the Badger project because we had to make a minimum order of 4.
That's as small as we have, currently.

Regarding your piston and bore damage, you either had a seizure or a partial or mini seizure. The scuffing damage at the quadrant locations that you describe is the description of the classic Bullet seizure. I have seen dozens and dozens of Bullet pistons with that on them.

The seizing comes from overheating the piston. It generally has these main causes.
1) The engine was operated at an rpm under the torque peak rpm with a wide throttle opening, which caused pinging(detonation) until the piston overheated and seized, or almost seized.
2) The ignition timing was too advanced, causing overheating with similar results.
3) The mixture was too lean, causing overheating with similar results.
4) All, or any combination of any of the above.

The fact that it is a 4-speed Bullet has a tendency to make riders stay in 4th gear at lower rpms too much, because the big 3rd-4th ratio gap causes a big rev when downshifting, and many riders don't want to do it. This ends up with a situation of lugging or near-lugging described in Scenario #1 above. It is important to not be grabbing large handfuls of throttle in top gear at lower rpms when climbing hills or riding two-up, or any loaded condition.
« Last Edit: May 16, 2015, 01:46:41 PM by ace.cafe »

Dhastings1954

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Re: Cylinder wear and compression
« Reply #6 on: May 17, 2015, 08:25:05 AM »
Has anyone used any of the Indian RE barrel/piston kits? NField Gear used to offer a 535 kit, but it appears to be out of stock and I am not seeing a standard 500 barrel/piston kit. I don't have access to a good machine shop in rural Vt that I think could do the cylinder re-bore. Am inclined to buy a barrel/piston set up if I can find one.
Vt Bullet

ace.cafe

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Re: Cylinder wear and compression
« Reply #7 on: May 17, 2015, 08:46:44 AM »
Has anyone used any of the Indian RE barrel/piston kits? NField Gear used to offer a 535 kit, but it appears to be out of stock and I am not seeing a standard 500 barrel/piston kit. I don't have access to a good machine shop in rural Vt that I think could do the cylinder re-bore. Am inclined to buy a barrel/piston set up if I can find one.

What you need is an alloy finned barrel with a good piston fitted to it.
The alloy barrel is much needed for cooling. The cast iron barrel is very poor for cooling.
As for pistons, there is one with a perfect record of reliability, and there are all the rest. I'll let you figure out which one it is.  ;D

High On Octane

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Re: Cylinder wear and compression
« Reply #8 on: May 17, 2015, 08:53:18 AM »
 ;D
Scottie J  ~  Bulldog Kustoms Denver  ~  1958 Enfield/Indian Trailblazer - The Blackhawk

cafeman

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Re: Cylinder wear and compression
« Reply #9 on: May 17, 2015, 09:40:16 AM »
I would not assume any cylinder as purchased will be bored correct or honed to fit the piston in any kit. It needs to be checked for taper and out of round. I sourced an alloy cylinder from Hitchcock's that was claimed to be ready for a standard sized 500 piston and it was slightly out of round. Also, the liner was porous but when bored to fit my chosen .040 over  piston I used it cleaned up. And finally, the threaded insert Hitchcock's install for the short head stud on the fiirst cylinder they sent me was not perpendicular (it was cocked) so the head bolt was slightly angled and the head could not be installed. More info than you asked for but worth checking.
Current Fleet: 2001 Royal Enfield Bullet 500 Cafe Racer
                     1996 Yamaha Seca II
                     1991 Husqvarna 350WXE
                     1991 KTM 250MX
                     2004 Husqvarna TC450