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Author Topic: Aluminum cylinder head  (Read 3323 times)

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Offline Canadiana

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Aluminum cylinder head
« on: June 20, 2016, 07:43:07 PM »
I have a stihl made about 1980-82. I'm wondering if i bore it out 2mm will it require a new nikasil treatment or will there be enough cast iron left on the cylinder. I found stihl replacement parts for a very unreasonable price compared to performance. I also found used replacements but i would have to import and am not sure what levies i would have to pay. I'm hoping to bore it out, improve performance  (slightly) and stick with the same carb. 38mm to 40mm doesn't seem to much. Thanks for any input
The saw is more fun than the purpose of the wood... the forest is trembling 🌳

Offline sawguy21

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Re: Aluminum cylinder head
« Reply #1 on: June 20, 2016, 10:09:03 PM »
Boring is not practical, the thin Nikasil coating would disappear and where would you find an oversized piston assembly. If the cylinder is in good condition you would see more improvement opening up the ports and muffler. Canadian FF member ehp is a wizard at this.
old age and treachery will always overcome youth and enthusiasm

Offline Al_Smith

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Re: Aluminum cylinder head
« Reply #2 on: June 20, 2016, 10:16:44 PM »
What model of saw is it to have a cast iron cylinder?

Offline DelawhereJoe

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Re: Aluminum cylinder head
« Reply #3 on: June 20, 2016, 10:28:20 PM »
The saw is what around 30-32cc, how much performance are you trying to get out of it. I'd say try to rebuild it to factory specs displacement wise and do all other mods you can to it, but at some point you hit the "should I really spend this much on an old saw with parts getting harder and harder to find"  train of thought. Don't forget about the sharpest chain you can put on it.
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Offline Canadiana

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Re: Aluminum cylinder head
« Reply #4 on: June 21, 2016, 11:15:35 PM »
Im nearly positive this cylinder is nikasil. I meant to collect a quote today on boring and replating but life  has a way...  The slightly larger piston is much easier to find and the cylinder head is very lightly scoured. All helpful observations so far TY.
The saw is more fun than the purpose of the wood... the forest is trembling 🌳

Offline joe_indi

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Re: Aluminum cylinder head
« Reply #5 on: June 22, 2016, 01:11:13 AM »
Since I have gone through the whole process of reboring a chainsaw cylinder to oversize I might be able to give you some info on the subject.
There is no cast iron in the bore the nikasil/hardchrome coating is done directly to the aluminum bore.
The coating is  extremely thin. And on an old bore it is not perfectly round so when you machine it you stand to get some spots that are going to remain untouched.
Being a cylinder cum head with the top end closed accurate machining to the top is going to be extremely difficult.
Getting an oversize piston that has the same shape for the same port timings are extremely slim.

Yes, I have done it, but differently and it took me quite a lot of trial and error and quite some expense before I have reached a workable stage, but not perfect.
I did it on the Stihl MS460 which has a 52mm piston as standard.
The 54mm piston of a MS660 was a mistake since it had longer skirts and too much of a different port timing.
I had a piston maker make me a batch of 52.5mm and 53mm pistons.
I had a machine shop bore out the cylinder insert cast iron sleeves after cutting out the ports.
And the sleeves were polished. It was a total failure!
with one end closed it was just not possible to do a perfect reaming. It used to be wider at the bottom and narrow at the top, plus intrusion into the squish area gave the saw unstable idle.
After going through about 10 cylinders we have arrive at a method that works at least 75%
The sleeve is reamed and polished outside the cylinder before it is hydraulically pressed into the cylinder.
The clearance for the piston is a 'go-no go', for which I use a method I have seen mechanics do in the late 50s on my dad's 1948 Ford V8.
An old piston is installed on a conrod, coated with oil and a then worked in the cylinder till it becomes a bit free.
Next the new piston is used on the conrod till it moves up and down by hand.
The engine is then assembled and started up. But for the flywheel to deliver adequate air and for the cylinder and piston to seat properly it needs to have some load, so I cut a few branches, progressing slowly to thicker wood.
After a couple of tankfuls it runs fine.
Even then it requires atleast a week of careful use before it is completely seated.
Done correctly things last indefinitely.
Some of the saws I have done this job on have completed 3 years and are still going strong.
The best part is that if the cast iron gets no damage from piston seizures. But at times a broken ring can damage it.
So I start with a 52mm bore, after a year or so it it can handle a 52.5mm with minimum machining and if the bore wears out enough it gets a 53mm.
With just a 0.5mm increase the torque increases noticeably, but I prefer to keep the maximum rpm at 13500.
With the 53mm I limit it to 13000.
I had uploaded some pictures some time ago.
http://www.forestryforum.com/gallery/thumbnails.php?album=2210

A few more pictures here:
http://www.forestryforum.com/gallery/thumbnails.php?album=2273


Offline joe_indi

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Re: Aluminum cylinder head
« Reply #6 on: June 22, 2016, 01:19:07 AM »
Boring is not practical, the thin Nikasil coating would disappear and where would you find an oversized piston assembly. If the cylinder is in good condition you would see more improvement opening up the ports and muffler. Canadian FF member ehp is a wizard at this.
Very true. For a one time job it is really not worth it. I am yet to clear my costs even after doing around 30 saws. Easier thing to do would be to improve airflow at both ends by modding the ports slightly and opening up the muffler and installing a bigger main jet.

Offline Ada Shaker

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Re: Aluminum cylinder head
« Reply #7 on: June 22, 2016, 01:32:41 AM »
There are places that specializes in electroplating cylinder bores and part thereof the exhaust port, but they generally specialize in doing motorbikes for racing and the like. I've heard the coating can be up to half a mm thick, there is however a specialised procedure for doing it like honing and the like. I guess if you have enough material to bore and clearances for the piston to travel any rebuilt of such nature would be possible. Longevity of the motor would be a different issue as with most race engines, rebuilds are more frequent as there are a lot more stress on internal components.
A rebuild of such nature is likely to cost more than just replacing the original jug/etc, imo. You may be paying less for the piston up front, but the electroplating procedure is likely to counter balance any savings, plus the additional stresses on the motor.
When a company sells millions of chainsaws globally, a saving of one dollar on the build of a saw equates to millions of dollars to the companies bott˛m line. I don't think they'll give you any more aluminium in the jug than what you really need to have the saw function as stock, anything else would be a compromise to the saws integrity, and perhaps a reduced life span.
If it hangs to the left, your likely to be a Husqvarna man.
If it hangs to the right, your likely to be a Stihl man.
Anything else is an uncomfortable compromise.
                             AND
Walking with one foot on either side of a barbed wire fence can become extremely uncomfortable at times.

Offline Canadiana

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Re: Aluminum cylinder head
« Reply #8 on: June 23, 2016, 08:35:43 PM »
Its a beutiful thing when a numbie (myself) can make a few inquiries and recieve some well written experience and opinion from the forum. At this point all of my ideas for repair have met their end but i am still interested in hearing more  trials and tribulations about rebuilds and accidentally going deeper and deeper into repairs. FYI: my piston and rings were certainly missing their machined surfaces. The cylinder however only a small line or 2 can be felt when rubbed carefully  (can't be seen).
The saw is more fun than the purpose of the wood... the forest is trembling 🌳

Offline celliott

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Re: Aluminum cylinder head
« Reply #9 on: June 24, 2016, 05:23:49 PM »
I'd ask around and search around for a used cylinder. I've had good luck that way. Lots of guys hold onto stuff like that, you just gotta ask.

What model Stihl is it?
Chris Elliott

Clark 666C cable skidder
Husqvarna and Jonsered pro saws
265rx clearing saw
Professional maple tubing installer and maple sugaring worker, part time logger

Offline Canadiana

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Re: Aluminum cylinder head
« Reply #10 on: February 22, 2018, 02:11:33 AM »
Since I have gone through the whole process of reboring a chainsaw cylinder to oversize I might be able to give you some info on the subject.
There is no cast iron in the bore the nikasil/hardchrome coating is done directly to the aluminum bore.
The coating is  extremely thin. And on an old bore it is not perfectly round so when you machine it you stand to get some spots that are going to remain untouched.
Being a cylinder cum head with the top end closed accurate machining to the top is going to be extremely difficult.
Getting an oversize piston that has the same shape for the same port timings are extremely slim.

Yes, I have done it, but differently and it took me quite a lot of trial and error and quite some expense before I have reached a workable stage, but not perfect.
I did it on the Stihl MS460 which has a 52mm piston as standard.
The 54mm piston of a MS660 was a mistake since it had longer skirts and too much of a different port timing.
I had a piston maker make me a batch of 52.5mm and 53mm pistons.
I had a machine shop bore out the cylinder insert cast iron sleeves after cutting out the ports.
And the sleeves were polished. It was a total failure!
with one end closed it was just not possible to do a perfect reaming. It used to be wider at the bottom and narrow at the top, plus intrusion into the squish area gave the saw unstable idle.
After going through about 10 cylinders we have arrive at a method that works at least 75%
The sleeve is reamed and polished outside the cylinder before it is hydraulically pressed into the cylinder.
The clearance for the piston is a 'go-no go', for which I use a method I have seen mechanics do in the late 50s on my dad's 1948 Ford V8.
An old piston is installed on a conrod, coated with oil and a then worked in the cylinder till it becomes a bit free.
Next the new piston is used on the conrod till it moves up and down by hand.
The engine is then assembled and started up. But for the flywheel to deliver adequate air and for the cylinder and piston to seat properly it needs to have some load, so I cut a few branches, progressing slowly to thicker wood.
After a couple of tankfuls it runs fine.
Even then it requires atleast a week of careful use before it is completely seated.
Done correctly things last indefinitely.
Some of the saws I have done this job on have completed 3 years and are still going strong.
The best part is that if the cast iron gets no damage from piston seizures. But at times a broken ring can damage it.
So I start with a 52mm bore, after a year or so it it can handle a 52.5mm with minimum machining and if the bore wears out enough it gets a 53mm.
With just a 0.5mm increase the torque increases noticeably, but I prefer to keep the maximum rpm at 13500.
With the 53mm I limit it to 13000.
I had uploaded some pictures some time ago.
http://www.forestryforum.com/gallery/thumbnails.php?album=2210

A few more pictures here:
http://www.forestryforum.com/gallery/thumbnails.php?album=2273
Pics and determination are unmatched. I thought i posted a thanks for these before but didn't. Great documentation. Thanks. Your independence is notable 
The saw is more fun than the purpose of the wood... the forest is trembling 🌳

Offline ehp

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Re: Aluminum cylinder head
« Reply #11 on: February 23, 2018, 06:54:13 PM »
find another cylinder. Most older cylinders were chrome bore not nikasil . And yes you need to have the cylinder wall plated by something , chrome bore uses different rings than nikasil bore , Nikasil is forsure a harder material than chrome . You can if you have to and run rings meant for chrome bore on nikasil bore . BUT DONOT run rings meant for nikasil bore in a chrome bore , the rings will peel the chrome right off the bore wall

Offline ehp

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Re: Aluminum cylinder head
« Reply #12 on: February 23, 2018, 06:58:49 PM »
another thing to is if the cylinder still has the combustion part still all one piece most of the places that do replating will not touch the cylinder as they want the head off . Its quite hard to spray nikasil and make the 90 degree turn in the bore and keep the piston skirt clearance correct , its a lot easier for them to do that job with the head part cut off

Offline Al_Smith

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Re: Aluminum cylinder head
« Reply #13 on: February 23, 2018, 07:28:38 PM »
Something about this is rather confusing .First of all if it were a cast iron lined cylinder it would not be plated with anything .Am I missing something here ?

Offline ehp

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Re: Aluminum cylinder head
« Reply #14 on: February 23, 2018, 09:00:05 PM »
never gave us what saw  engine number it was but from the 80's just figured chrome bore as most were back then

Offline Al_Smith

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Re: Aluminum cylinder head
« Reply #15 on: February 24, 2018, 03:41:51 AM »
Yes the whole thing is confusing to me .

Offline Canadiana

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Re: Aluminum cylinder head
« Reply #16 on: February 24, 2018, 08:16:56 PM »
Something about this is rather confusing .First of all if it were a cast iron lined cylinder it would not be plated with anything .Am I missing something here ?
You aren't missing anything. Lol. It was aluminum/nikasil. No surprise there. The saw (parts only) is long gone. Price vs performance was not going to work out. Importing used parts just didn't seem reasonable. It was reborn as parts
The saw is more fun than the purpose of the wood... the forest is trembling 🌳

Offline Grandedog

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Re: Aluminum cylinder head
« Reply #17 on: March 01, 2018, 02:31:04 PM »
   Howdy,
   Nikasil is only about .010 - .012 thick. Chrome is harder and also more difficult to do correctly. Chrome doesn't bond as well as nikasil. If you look at cross sections of cylinders under an electron microscope, chrome has a very defined line where it bonds to the aluminum. A cross section of nikasil blurs the line and, shows the nikasil actually impregnating the aluminum cylinder. This is one of the main reasons why chrome will flake and nikasil won't. Chrome cylinders are more likely to fail with port mods because you expose the edge of the chrome.
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