Hi everybody,long time lurker here.I have a couple of questions concerning my Makita 6421.I have been looking at a 7900 big bore kit for it.Is this a stock type bolt up kit?Simply change the piston,ring,and head?Also,I read about "squish".Removing the head gasket and advancing the timing.Does advancing the timing consist of slotting out the mounting tabs on the coil and moving up or down ?These might seem like dumb questions ,but I honestly have no experience with modifying saws.Thanks for any help.Also,great site yall have here with plenty of great advice.
Makita 6421 questions
- Thread starter Bubster
- Start date
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Fatherwheels
Addicted to ArboristSite
First off, your better going for the original Makita 7900 cylinder and piston.
The bigger bores / 84cc drink fuel, and do not put out the expected power, the 7900 makita
top end is the better choice. There is a difference in these cylinders too, in that the decomp
valve is not on the same place, you need to check this out, a top cover with a hole in
the correct side to suit the valve is an option at more expense of course.
Others who know the exact details will chime in soon.
There is no seporate head on a chainsaw, there is a gasket between the bottom of the cylinder
and the bottom end it bolts on to, this can be removed if there is enough space between
the top of the cylinder and piston, this gap has to be measured to see if the gasket can be removed.
Even if you can remove it you will need a suitable sealer between the joint.
The bigger bores / 84cc drink fuel, and do not put out the expected power, the 7900 makita
top end is the better choice. There is a difference in these cylinders too, in that the decomp
valve is not on the same place, you need to check this out, a top cover with a hole in
the correct side to suit the valve is an option at more expense of course.
Others who know the exact details will chime in soon.
There is no seporate head on a chainsaw, there is a gasket between the bottom of the cylinder
and the bottom end it bolts on to, this can be removed if there is enough space between
the top of the cylinder and piston, this gap has to be measured to see if the gasket can be removed.
Even if you can remove it you will need a suitable sealer between the joint.
buy the piston and cylinder kit for a PS-7900.....it will come with the correct top cover, decomp valve, cylinder, piston. it is the same cost as just the cylinder and piston. 038130910 is the part number you want
dont waste your time or money on the aftermarket big bore kits. they dont perform any better than the stock 7900 top end and arent anywhere near the same quality
dont waste your time or money on the aftermarket big bore kits. they dont perform any better than the stock 7900 top end and arent anywhere near the same quality
Will the stock muffler and carb be sufficient?Thanks for the replies
if it has a cat muffler you need to gut it. other than that they are the same.
drumbum
ArboristSite Operative
Going from the stock 64cc to an 84.7 cc BB is an upgrade in power, and can get good results, depending on the kit.
I don't remember anyone asking about going from factory 79cc to BB in a long time.......
I don't remember anyone asking about going from factory 79cc to BB in a long time.......
I added a new big bore kit to my 6401 about nine years ago. I had loaned it out and the borrower straight gassed it. The upgrade worked out very well and I noticed a definite power increase. I bought the Meteor parts from Northwood Saws. Not cheap but effective. This saw occasionally pulls a 32" bar rather easily, but I usually run a 25". One of my buddies has a 6421 with a BBK that can pull a 32" bar when ripping hardwood using an Alaskan sawmill:
He loves this saw.
He loves this saw.
Fully factory stock and original, with a MILD muffler mod, my Dolmar PS-7900 will pull a 36" 3/8" B&C setup all day long, both bucking and/or noodling beech and oak!
OEM 52mm P&C FTW!!!
OEM 52mm P&C FTW!!!
