# Makita Concrete Saw



## stevnpayn (Oct 30, 2008)

I have 10 Makita DPC7311HD Concrete Saws that i rent out. They are three years old, and well maintained. When i rent the saws to customers, i send them with a gallon of premixed fuel, so the customer doesn't put regular gas in the two strike engines (which cause my last saw to blow). This past month I have had three engine blow, the compression went from 125psi, to 75psi, and there is scaring on the piston and cylinder. I haven't changed the prep or maintainance in the past three years. And the customers are using the fuel i provide. I use a 50:1 mixture 87 octane with 2 cycle engine oil from Stens. Is there a different oil i should be using for and older engine? Or is there something else causing this? I would appretiate any knowledge or theories you could pass my way.


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## Basementgeek (Feb 7, 2005)

Hi and welcomwe to the forum :wave:

Sure sounds like a lack of lubrication to me also.

I would go about 30:1. 50:1 always scares me, just so little oil.
I think the worst than can happen is that the plug may not last as long. Plugs are cheap !!!

I"m kind of old and believe 2 cycle engines should have a little blue tinge to the exhaust.

BG


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## MrChooks (Apr 19, 2008)

Tks BG - 

I wasn't game enough to show my age - but I agree, 50:1 = stuff all oil - regardless of what the OEM manufacturers say

Old codgers like me were used to nasty little 2 strokes that used 1/4 pint to the gallon (about 30:1) and got used to a bit of blue smoke and black plugs - but at least we didn't seize pistons and bores.

The old 30+/- : 1 mix mightn't have been all that environmentally friendly - but I can't help but feel todays 2 stroke makers are getting their _enviro brownie points _by poor lubrication advice.

So as BG says - if its a 2 stroke and you can't see blue smoke in the exhaust - the engine isn't being lubricated - after all, *the only oil it gets is what you introduce in the fuel mix* - if there isn't enough there to give a blue tinge to the smoke - an old fart like me would say there isn't enough there to lubricate the bore, big end and main bearings:4-thatsba


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## nego-oh-oh (Jan 22, 2006)

also consider that your customers are using more 
than the gallon you are providing them with.
send a unopened container of oil with the rental
unit (always refund their money if unused) 
check the returned gas by holding a sample
up to the light-in a clear container, the color 
difference should tell if they added more gas,
and not any oil-this may explain the piston scarring.


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## stevnpayn (Oct 30, 2008)

Thank you for the input gentlemen, i will change my fuel ratios.


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## MrChooks (Apr 19, 2008)

:wave:No probs and hope we helped.

Just to satisfy this old fart (and maybe BG) - once you increase the oil ratio - pls let us know how you get on - as I, (like BG) have always winced at the 50:1 oil ratio. - have always thought 50:1 wasn't enough oil to dirty your hands, let alone lubricate high speed moving parts!!

If you find that 30+:1 is fouling plugs too much - you could increase the ratio to somewhere in between - say 40:1 and see if that corrects any dirty plug issues you might be having.

In the end and as BG said - plugs and oil are cheap - much cheaper than scored bores.


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## rbragg11 (Jan 25, 2009)

Be careful with the rich oil mix. In my part of the world running too rich of a mix in todays lean running handheld causes exhaust ports and mufflers to stop up with carbon. If you want to go to a richer mix try a 40:1. This usually extends the distance between exhaust cleanings and provides plenty of lubrication.


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