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Author Topic: Inexpensive pistons?  (Read 1431 times)

geoffbaker

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Inexpensive pistons?
« on: February 09, 2008, 12:47:40 PM »
I'm looking for an inexpensive piston to replace the worn piston on my bullet. The current piston is about .006 worn; the manual says up to .008 can be used but after that replacement is needed.

The only one I've seen in the US is a performance piston offered by Classic Motorworks for $289 which is too much for my needs. I've seen them sold in England for only about $120 for a standard or +020 oversized piston.

Any good source here in the US for cheaper pistons?

Thanks!

fredgold52

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Re: Inexpensive pistons?
« Reply #1 on: February 09, 2008, 01:35:58 PM »
Geof,  I'm sure you looked here but there seems to be some on this page in the CMW Store.

http://www.royalenfieldusa.com/store-clearance-overstock-c-1_13.html

Clearance and all that.

$100 is about normal for a piston these days.

If the piston is worn .006, how much is the cylinder bore worn?  I ask because there's an oversize piston on that page too.
2006 '65' and a 200cc Stella, Indian all the way

SRL790

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Re: Inexpensive pistons?
« Reply #2 on: February 10, 2008, 06:21:28 AM »
Geof,

I seem to remember from another one of your posts that this bike only has 5000 miles on it.  Seems kind of low to be replacing a piston because of wear.

When measuring the piston be aware that it is oval and tapered and that you are measuring in the correct location.  You also need to check the bore very carefully, not just for diameter, but that it is straight.

You probably already know all this, but just making sure before you spend a bunch of $$$ you don't have to.

Andy
Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

geoffbaker

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Re: Inexpensive pistons?
« Reply #3 on: February 10, 2008, 09:19:52 AM »
Thanks for the info. I've decided to hold off on replacing the piston yet. The manual says .008 is the max, so I've got a little time with .006

Regarding measurements, I'm just relaying what the machine shop is telling me. I'll talk to them some more.

As I plan on replacing the engine within the next couple of thousand miles anyway (with a diesel I have purchased), I'm just looking to get the bike running again for a month or two, so I can get it registered & inspected; plus I wanted to have some fun in the meantime :)

cyrusb

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Re: Inexpensive pistons?
« Reply #4 on: February 10, 2008, 01:01:42 PM »
It seems that you could use a lot of pistons in 5000 miles if you don't break them in slowly ( google and read" Travelluna"). I never knew how hard it was to ride slowly until I broke mine in. If it sticks once, its time for a new piston. This break in procedure is tough in modern traffic. Also it may be a false economy to use an inexspensive piston, the one you are replacing may have been one.
« Last Edit: February 10, 2008, 02:36:56 PM by cyrusb »

fredgold52

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Re: Inexpensive pistons?
« Reply #5 on: February 10, 2008, 05:52:25 PM »
If it sticks once, its time for a new piston.

It's been my experience that is not necessarily the case.  Whether or not a piston needs to be replaced after a seizure depends entirely on how much actual damage was done.

In the case of a 'locked up' piston where there is much scoring on the skirt and the ring grooves are even smeared, replacement is the only alternative.  Conversly, if the damage is light with only mild scoring in one or two small locations, the piston can be lightly sanded smooth, any aluminum deposits removed from the bore, buttoned up and run it again. 

I know this doesn't sound like a good practice, but many 2 stroke scooter riders (read Vespa and Lambretta) are riding around on lightly seized pistons with no ill effects at all.  On a practical level where people have more time than money, this sort of thing is done alot.  A long time ago, I had a 125cc Moto Guzzi Sport that seized up pretty good a couple of times.  All it needed was a light clean up and it was good to go again.

I expect I'll get flamed on this one, but I feel I need to post it just the same.
2006 '65' and a 200cc Stella, Indian all the way

cyrusb

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Re: Inexpensive pistons?
« Reply #6 on: February 10, 2008, 07:37:34 PM »
I also have seized a vespa(p125x) and got away with it, sometimes you do. I think it was on the second seizure that I actually had to tear it down the slap was so loud. I can remember it was so sudden, then trying to pull the clutch lever in , but its straight down when your in last gear, not easy to grab in a locked up slide. They rarely locked up going slow.

SRL790

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Re: Inexpensive pistons?
« Reply #7 on: February 11, 2008, 05:20:59 PM »
I think I touched on this in another thread some time back but my Enfield did actually seize after it's rebuild.  Athough after it cooled off I was able to restart the bike and continue my trip I decided I'd better take a look. 

I should mention that I bought the piston and barrel already already bored as a "matched" set.

After pulling it apart again I found the piston to have only light scoring and, as Fred said, I removed any burrs and re-used it.  This is when I got into measuring the piston accurately (like I shoud have done the first time I installed it).  I found that the piston at its widest point (fore and aft at the base of the skirt) was actually below the minimum clearance.  I had a machinist friend run a precision hone through the bore and open it up an additional 0.002". 

Since then it has over 2000 miles and has ran fine.

So Geof, this is why a made my earlier comment about carefully checking the piston diameter.
Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

cyrusb

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Re: Inexpensive pistons?
« Reply #8 on: February 11, 2008, 08:19:02 PM »
How did this worn piston get your attention? Was it clacking? The reason I ask is it might not be a bad thing to have a slightly loose piston, as long as it doesn't slap. After all this is an Enfield.

fredgold52

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Re: Inexpensive pistons?
« Reply #9 on: February 11, 2008, 08:38:23 PM »
I had a machinist friend run a precision hone through the bore and open it up an additional 0.002". 

Since then it has over 2000 miles and has ran fine.

So Geof, this is why a made my earlier comment about carefully checking the piston diameter.

Interesting experience.  What pistopn/cylinder clearance did you wind up with?  I ask because somewhere else on the forum someone talked about honing their cylinder out until they had .007 clearance.  I suggested that might be a little much and that it might have been better to stop at about .004.


Just for grins, does anyone know what the factory specification for this clearance is? 
2006 '65' and a 200cc Stella, Indian all the way

SRL790

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Re: Inexpensive pistons?
« Reply #10 on: February 12, 2008, 02:07:15 PM »
Fred,

Once I had it all on the bench where I could measure it accurately the clearance at the widest part of the piston was only 0.002" (and remember this was after about 1000 miles of break in).  I opened this up to 0.004".

Cyrusb,

I did not have any abnormal noises. I just knew that it had seized and should, per my Owner's Manual, "have a qualified mechanic ease down the high spots on the piston".  The piston was in fact too tight, not loose.
Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

cyrusb

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Re: Inexpensive pistons?
« Reply #11 on: February 12, 2008, 02:21:23 PM »
Actually that question was for the original poster, Geoffbaker.

SRL790

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Re: Inexpensive pistons?
« Reply #12 on: February 12, 2008, 02:29:41 PM »
Actually that question was for the original poster, Geoffbaker.

Oops :-[
Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

geoffbaker

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Re: Inexpensive pistons?
« Reply #13 on: February 12, 2008, 04:08:42 PM »
cyrusb,

the piston never got my attention. After purchasing the bike in Las Vegas and riding it to Tucson, it died at the end of the trip. (It became progressively harder to start during the course of the drive).

Compression was 30psi. When I took of the head to find out why, I found the head and cylinder were extremely carbonized. I took the head and piston and cylinder into a machine shop for measurement, and they reported there was .006 gap between piston and cylinder; the manual says new is .002, .008 is extreme wear and needs replaceement.

The piston was never a problem. The valves weren't closing properly due to the carbonization, hence the low compression.

Turns out the carb jet setting was for max richness, and there was rust in the tank. I assume as the previous owner found it running poorly, he kept enriching the mixture.

With new valves and a clean head, I'm hoping the piston wear will not be too excessive and the bike should be operable. I'll let you all know!