Makita 6401 piston upgrade

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Jon Tyler

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I've seen some people upgrading their Dolmar/Makita 6400/6401 with a piston that "makes it a 7900? Am I reading this correct or is there more to this than meets the eye? -IF- this is true, will a modded 6401 run with stock stihl 460 and husky 372?




Jon
 
Jon Tyler said:
I've seen some people upgrading their Dolmar/Makita 6400/6401 with a piston that "makes it a 7900? Am I reading this correct or is there more to this than meets the eye? -IF- this is true, will a modded 6401 run with stock stihl 460 and husky 372?




Jon
Click to expand...

Yup, what huskydave said, a Dolmar 7900 cylinder kit will fix it right up. Just bolt it on stock and it will smoke the 460 and the 372.
 
RiverRat2 said:
May as well @ least Mod the muffler while you are there Eh????? :clap:
Click to expand...

That is about all that works on a 7900 unless you change the coil. Any porting and they cant reach the power band before the limiter catches.
 
I bought 3 of the 6401's that need p & c's. I may just do 1 of the 79 cc set ups and sit back and wait on what develops with the bb kits. Would be nice to find a source for the non-limited ignition modules...........:popcorn:
 
cuttinscott said:
http://www.arboristsite.com/pp-classifieds/showcat.php?cat=500&ppuser=3404


We sell quite a few of these kits to PS6400/6401 users its a simple upgrade to make a 79cc saw from your 64cc saw. same carb same everything else just install new P&C and go have fun.



Scott
Click to expand...

Grande Dog said:
Same here:
http://www.baileysonline.com/itemdetail.asp?item=DM+038+130+030&catID=

http://www.baileysonline.com/itemdetail.asp?item=DM+965+531+121&catID=

We have a Big Bore kit in the pipeline for these. I haven't seen the prot-types yet so they're a ways off in the future.
Click to expand...

I am $8.80 cheaper on this than baileys after shipping.

Also ANY big bore kits that may venture into this market will not be from DOLMAR but from a aftermarket source and probably inferior quality.

Scott
 
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Remembering for a moment that there are some of us who don't have a fraction of the saw maintenance expereince that many here have-and even some of us who have never broken down a saw beyond changing the filters and replacing a sprocket. With that as background info, just how complicated would it be to switch out the P&C on a 6401. Presumably there is a single connecting rod (bearing and race assembly) that attaches to the crankshaft in a similar fashion to an auto engine except obviously there is only one piston. What are the potential trouble spots of this procedure.

Thanks in advance for all constructive advice.

Hugenpoet
 
Hugenpoet said:
Remembering for a moment that there are some of us who don't have a fraction of the saw maintenance expereince that many here have-and even some of us who have never broken down a saw beyond changing the filters and replacing a sprocket. With that as background info, just how complicated would it be to switch out the P&C on a 6401. Presumably there is a single connecting rod (bearing and race assembly) that attaches to the crankshaft in a similar fashion to an auto engine except obviously there is only one piston. What are the potential trouble spots of this procedure.

Thanks in advance for all constructive advice.

Hugenpoet
Click to expand...

Hi Hugenpoet, To answer your Question about top end swap on a PS7900.
First remove air filter and cylinder covers, air cleaner and blow all debris from top of the saw especially around the cylinder base., Then Remove the muffler and carburetor with your T-27 torx and clean some more, then remove the 4 bolts that hold the cylinder down again with your T-27 torx. unbolt the AV mount from the cylinder and carefully lift the cylinder off the piston. with a small pair of needle nose pliers remove the circlip form the piston and carefully push the piston pin out of the piston. inspect and reoil the wrist pin bearing. carefully remove any gasket material that stayed attached to the crankcase. Now install the new piston to the rod with the arrow pointing tward the exhaust. Install the new cylinder base gasket on top of the crankcase and compress the ring with a suitable type ring compressor oil the bore of the new clean cylinder and carefully push the cylinder down over the piston. line up the holes and bolt the cylinder down and tighten. I forgot to mention to swap the carb intake boot when the cylinders are off in your hands this can be done on the saw but is easier to do while the jug id unattached. Now reinstall the muffler, av mount and carb and filter and hoods richen the carb adjustments a tad and start. It will smoke initially due to the lube you wiped inside of the cylinder wait for the smoke to clear check the running and acceleration of the saw and go cut some wood and have fun.

If your not comfortable with this job I charge approx. a half hour labor + shipping to do this for you.

Scott
 
Last edited:
Hugenpoet said:
Remembering for a moment that there are some of us who don't have a fraction of the saw maintenance expereince that many here have-and even some of us who have never broken down a saw beyond changing the filters and replacing a sprocket. With that as background info, just how complicated would it be to switch out the P&C on a 6401. Presumably there is a single connecting rod (bearing and race assembly) that attaches to the crankshaft in a similar fashion to an auto engine except obviously there is only one piston. What are the potential trouble spots of this procedure.

Thanks in advance for all constructive advice.

Hugenpoet
Click to expand...

if you havn't done this before, you may be better off having a shop do it. experiment on a cheapy.
 
Thanks Cuttinscott. Appreciate the detailed description. I will probably attempt to do it myself, I will just take a lot of extra time attempting not to screw things up.

Thanks again for taking the time and making the effort on my behalf.

Hugenpoet
 
cuttinscott said:
Also ANY big bore kits that may venture into this market will not be from DOLMAR but from a aftermarket source and probably inferior quality.

Scott
Click to expand...

i suspect quallity will not be an issue. lets wait to reserve judgement until something materializes.


:cheers:
 
CuttinScott left out a small safety tip

Before you remove the circlip stuff a shop rag down into the case.. and wrap another one around the rod.. That way if you drop it, it will only get lost on the magnet on the flywheel.. (Or so I have heard) LOL
 
ericjeeper said:
Before you remove the circlip stuff a shop rag down into the case.. and wrap another one around the rod.. That way if you drop it, it will only get lost on the magnet on the flywheel.. (Or so I have heard) LOL
Click to expand...

Best tip of the day.:clap:



I knew a guy years ago who dropped one of the "v" blocks out of a tap wrench down the carburetor of a 283 Chevy engine. Took about a week for that little piece of harden steel to work it's way through the intake manifold and through a intake valve and into a cylinder. It wasn't very pretty.
 

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