Dolmar 7900 / 7910 piston options

[NPKenny]

I built up a Makita 6401 a few years back with an OEM 7900 cylinder and piston. I ported it and was very happy with the results. I subsequently gave it to my BIL who got a few years of service out of it. I just got it back to repair because wasn’t running right....

The impulse line was cracked and the piston is scored. Transfer is minimal on the cylinder.

1. What are the current piston options? Multiple old threads mention 046 or 372BB as possible options but none of the comparison pictures are live. OEM 7910 piston is $100.

2. What is the best aftermarket BB kit? I have another 6401 that I might do some swapping with and keep the ported cylinder.

Thanks!

 

[huskihl]

I have a 7900 with a Golf piston in it. Seems fine. The oem cylinders run better than the aftermarket big bores usually

 

[dahmer]

@fordf150

 

[NPKenny]

I have a 7900 with a Golf piston in it. Seems fine. The oem cylinders run better than the aftermarket big bores usually

I am looking at cleaning up the OEM cylinder for one saw and possibly fit the BB on one saw. I would likely keep the OEM saw. No question the OEM runs great.

 

[dustinwilt68]

Save your money, the BB kits are junk from NWP

 

[huskihl]

I am looking at cleaning up the OEM cylinder for one saw and possibly fit the BB on one saw. I would likely keep the OEM saw. No question the OEM runs great.

I'd look for a used one on ebay. 73xx and 79xx cylinders pop up now and then

 

[smokey7]

Is the golf piston a 7900 style or 7910 style? Of the 5 or 6 golf pistons i had issues with 2. One lost part of the piston above the top ring and the crown at a transfer port. The other had short crown height by .018 and the locating pin was basically in the center of the ring groove. I still used it as the jug was machined to run a gasket so i just ran it no gasket and my numbers were still close enough.

 

[huskihl]

Is the golf piston a 7900 style or 7910 style? Of the 5 or 6 golf pistons i had issues with 2. One lost part of the piston above the top ring and the crown at a transfer port. The other had short crown height by .018 and the locating pin was basically in the center of the ring groove. I still used it as the jug was machined to run a gasket so i just ran it no gasket and my numbers were still close enough.

It's a windowed one for a 7900

 

[dustinwilt68]

A good dealer should be able to get you a new kit for 175.00, I just got my kit today, took it a week to get here

 

[fordf150]

Is the golf piston a 7900 style or 7910 style? Of the 5 or 6 golf pistons i had issues with 2. One lost part of the piston above the top ring and the crown at a transfer port. The other had short crown height by .018 and the locating pin was basically in the center of the ring groove. I still used it as the jug was machined to run a gasket so i just ran it no gasket and my numbers were still close enough.

skirt length is shorter on the golf pistons along with a slightly lower crown height. white box china pistons were closer but a few of the ones i bought to try had skirts that were .020-.035 narrower than oem.

 

[dahmer]

I built up a Makita 6401 a few years back with an OEM 7900 cylinder and piston. I ported it and was very happy with the results. I subsequently gave it to my BIL who got a few years of service out of it. I just got it back to repair because wasn’t running right....

The impulse line was cracked and the piston is scored. Transfer is minimal on the cylinder.

1. What are the current piston options? Multiple old threads mention 046 or 372BB as possible options but none of the comparison pictures are live. OEM 7910 piston is $100.

2. What is the best aftermarket BB kit? I have another 6401 that I might do some swapping with and keep the ported cylinder.

Thanks!

Just contact fordf150, great Dolkita dealer.

 

[NPKenny]

Just contact fordf150, great Dolkita dealer.

No question. He’s taken care of me in the past.

On the BB, I was hoping to avoid the 7910 cylinder differences and spending extra money I probably will never be reimbursed for.

@fordf150 What are current prices on a piston kit and cylinder/ piston kit? Thank you!

 

[Marshy]

Following.

 

[Deets066]

If you don't mind making a spacer you could run an 046 piston. Or 272 piston, just my take some measuring and adjusting.

 

[Deets066]

have to run the 46 piston backwards though

 

[Time's Standing Stihl]

Hyway makes a windowed 7900 piston.

You can find it on evilbay for less than $25 shipped

 

[Lightning Performance]

What single ring can be swapped into the NPW 54mm bb kit?

My NPW kit is slated for beam and mill duties. The other one is staying a 47mm triple transfer open OEM. Stability is the main goal.

How were the rest of the white box pistons looking?
@fordf150

 

[jacob j.]

What single ring can be swapped into the NPW 54mm bb kit?

The Poulan Pro 505/Jonsered 2083 piston would be a candidate. It's a 54mm, single ring slug that uses a 12mm wrist pin.

 

[Lightning Performance]

The Poulan Pro 505/Jonsered 2083 piston would be a candidate. It's a 54mm, single ring slug that uses a 12mm wrist pin.

Is this a buy the bearing deal or dig for one?
I can dig if other candidates "pop up."

 

[Lightning Performance]

The jug I have could use some serious intake area! Not ported, yet.