MS 460 advice

[Ledburyjosh]

Hi I have a 2009 MS460 which has been and still is a great saw.

 

Last year I added a duel port exhaust and retunned the engine to 2700 idle and 13,000H.

To do this I did remove the limiter caps. 

 

Recently I the saw kept stalling during idle and was running sloe on the top end.

 

So I have just checked and reset it. It was at 2200 idle and 11200H. So back to 2700 idle and 13000H.

 

I have noticed that the H screw is pretty much all the way in so no more future adjustment.

For now this is OK.

 

I wander how to manage this when it needs adjusting again.

 

Is there a way to accurately reset all screes without the limiter caps? Is it just the saw getting old and on its last legs? 

 

Any advice would be great thanks

[spudulike]

Your question "is this OK".....No, it isn't.

Having had a few machines in and played around a bit, from experience, when a machine needs the H screw wound in further than it should to make high revs, it generally means that your piston is well past it, the saw is low on compression and the only way to get the engine to hit high revs is to lean the saw right down.

The good news is that hopefully, the issue is with a worn piston and not the bore but you will need to strip the top end down, inspect the bore and plating and then the piston. 

You should be able to fit a Meteor or Hyway piston, roughen up the bore and fit, retune and it should be back to A1.

If the bore plating is worn then it is more likely on the inlet side through fine sawdust getting past the air filter and that means a new top end. It is possible the piston has nipped up but again, a new piston and a bit of cylinder work should bring it back.

The 460 is a pretty strong saw and have seen 046s in 20 years old and still very usable.

The compression on these saws is generally 160-170 psi which is pretty high on a large saw. I would suspect that yours will be around 140 so test if you can.

 

 

[Ledburyjosh]

Thanks for an incredibly useful answer again.

 

I do know fine sawdust does have a habit of getting past the filter on this saw and always has. I've tried several filter types to help. But when ever I clean it there is always fine dust stuck to the plastic the wrong side of the filter. So I wouldn't be surprised if the bore is worn. Perhaps I need to try and update the filter system when intake it apart.

 

When you say toughen it up up a bit, could you explain what's meant by that?

 

Thanks

[Ledburyjosh]

I shall order a pressure checking thing and report back.

 

Is there a way to determine if it is the bore or piston visually?

 

Can bores be replaced and if so is it economical to do so?

 

What I'm trying to think of is if I order a piston and fit that to find the problem still persists then it was the bore. Is there a systematic way of diagnosis to figure if it's the bore or piston without replacing the piston to find out it was the bore?

 

Thanks

[pleasant]

3 hours ago, StephenMews said:

I shall order a pressure checking thing and report back.

 

Is there a way to determine if it is the bore or piston visually?

 

Can bores be replaced and if so is it economical to do so?

 

What I'm trying to think of is if I order a piston and fit that to find the problem still persists then it was the bore. Is there a systematic way of diagnosis to figure if it's the bore or piston without replacing the piston to find out it was the bore?

 

Thanks

Well, not really...comes down to eye and experience deciding whether a cylinder is reusable. If you would rather not do the job twice and know you have a defined datum point, then my advice would be to replace both cylinder and piston as a matched pair. The pattern brands spud has mentioned are good and not overly expensive. As a dealer we would always fit as a matched pair (OEM parts only) as the customer would baulk at us charging him/her twice for doing the job if we find re-using a used cylinder with a new piston is not compatible. We need to ensure the job is right first time. If it's your time and labour it's not so much an issue. A meteor pot and piston set are good and not a fortune for peace of mind knowing both parts are new

Edited January 20, 2023 by pleasant

[Muddy42]

4 hours ago, StephenMews said:

Is there a way to determine if it is the bore or piston visually?

 

Unscrew the muffler and take a look in the exhaust port with a headtorch whilst pulling the starter cord.  Clamping the saw to a workbench helps.  You'll easily be able to see what the piston and rings look like.  Post a photo or video here if you want?

[pleasant]

44 minutes ago, Muddy42 said:

 

Unscrew the muffler and take a look in the exhaust port with a headtorch whilst pulling the starter cord.  Clamping the saw to a workbench helps.  You'll easily be able to see what the piston and rings look like.  Post a photo or video here if you want?

I would strongly advise removing the spark plug lead before pulling it over with you face near the chain and exhaust port....even if the switch is in the off position.

[spudulike]

13 hours ago, StephenMews said:

I shall order a pressure checking thing and report back.

 

Is there a way to determine if it is the bore or piston visually?

 

Can bores be replaced and if so is it economical to do so?

 

What I'm trying to think of is if I order a piston and fit that to find the problem still persists then it was the bore. Is there a systematic way of diagnosis to figure if it's the bore or piston without replacing the piston to find out it was the bore?

 

Thanks

If you order a compression gauge, buy the Gunson HiGauge as it works, some are specifically OK for cars but small engines produce a much small volume of air so don't register the actual engine compression.

 

Checking the bore - the visual check on the exhaust side as discussed earlier is fine. Just move the piston down to near the bottom of its stroke and visually check the bore through the spark plug hole. You can shine a small LED torch down the hole to help.

No need to pull the saw over and risk burning the hairs off your arm like I did once!

You can then raise the piston to cover the exhaust port and inspect the piston ring and skirt. It shouldn't have any deep vertical black lines on it.

To SEE if the bore plating is worn through (only seen this a few times so is rare), you will need to remove the cylinder and inspect the bore on the inlet side. If the plating has worn through, it will be a lighter in colour as you will be seeing patches of aluminium rather than the Nikasil plating. 

 

You have a few methods to check a piston....Calipers to measure the diameter and compare to a new piston.

 

You can measure the depth of the piston rings inner to outer surfaces front and both ends and compare to a new part.

 

You can push the piston ring in to the bore so it sits square and measure the end gap...7 thou is good, anything over 20 thou is getting bad....sorry about using imperial!!

 

A simple check is to take the piston, put it in the base of the cylinder and try to rock it forward and back. If you have done a few, you will be able to feel any excessive wear. 

 

The other technique is to put a ringless piston in the bore, cover the spark plug hole and then pump it up and down the bore. A badly worn piston won't create much of a feeling of compression when pushing the piston in to the cylinder.

 

You can purchase aftermarket cylinder and piston kits - typically £70-95 for anything decent and the OEM part £195.

When I said "roughen the bore" - this can be done with wet and dry paper or a small cylinder hone but if you do this, don't get the hone snagged in the lower transfers or exhaust port. Ball hones are available but are pricey.

 

Long and short...check the piston and bore visually by removing the plug and muffler. Get a pic up on here of the piston front. If you can see the original machining lines, the piston is probably fine...pics replace a thousand words!! 

If the saw has seen many hundreds of hours use, it is probably the piston so take the cylinder off...more pics for second opinion and fit a new piston if the bore is good.

If you do change the piston, fit it the correct way round and take A LOT OF CARE fitting the circlips....open ends towards the crankcase!

 

[Ledburyjosh]

Thank you. I shall get some pictures. It will be a couple of weeks until I start on it as I need to borrow a saw first to keep me going whilst fix this one.

 

To make sure I understand. The Bore and cylinder are not the same thing is that correct?

[Mark_Skyland]

Have a check of the metering side of the carb, the cover has four screws. Pull the cover off and see if it's full of fine sawdust. I've seen this before and the sawdust was making it over fuel.