Dolmar 7900 Big Bore Kit Review

[blsnelling]

I've got a saw to install it on now, so it's time for the details of the prototype BB Kit I have here. Bore size is 54mm resulting in a displacement of 85cc, up from 79cc stock. So far I've visually inspected, measured specs, and taken pictures. I've not yet put the parts on my saw. That will come soon enough. The P&C look very good. I intend for this is to be a fair honest report. Please keep this thread clean and on topic as I would like for it to be something of a product review than can be useful to others.

Here's some of the specs.

1. Piston Weight = 2.8 oz
2. Wrist Pin Weight = 0.6 oz
3. Cylinder Weight = 20.8 oz
4. Crown thickness above top ring groove = 0.130". Plenty of room for a popup.
5. Ring thickness = 0.047" = 1.2mm
6. Ring end-gap = 0.008"
7. Piston to cylinder clearance = 0.0025"

Here are some notes I've made so far.

1. There is one small knick in the cylinder wall well below the exhaust port. It's very small and will hurt nothing. The NiSi is not damaged.
2. Stihl style circlips are now used and the piston is relieve likewise for removal. A nice improvement the customers have called for.
3. The ports are very nicely beveled.
4. The NiSi coating and honing looks nice.
5. The piston skirt does not even come close to freeporting the exhaust port at TDC.
6. There is room for widening the ports, but not as much as with the 361 kit. Should be enough for modest gains.

 

[blsnelling]

 

[spacemule]

Brad, I like your pictures--on topic and in focus. I'm curious though--is someone supplying you with these kits for the purpose of evaluation, or are these purchases of your own initiative?

 

[blsnelling]

These are prototypes for the purposes of evaluation. They will not be on the market for probably at least a couple more months.

 

[stihl only]

Could the knick be from poor packaging of the wrist pin? Have seen that on some kits.

 

[JONSEREDFAN6069]

let me know how it works out, I have a 7900 will this fit on it?

 

[spacemule]

These are prototypes for the purposes of evaluation. They will not be on the market for probably at least a couple more months.

Cool. Does that mean there is still room for constructive criticism and suggestions to be implemented?

 

[scotclayshooter]

Looks like a lot of scope for lightening the piston.

 

[scotclayshooter]

Whats the CCs going to be?
Doh read it twice and didnt notice 85CC

 

[blsnelling]

Cool. Does that mean there is still room for constructive criticism and suggestions to be implemented?

Shoot away. I'm sure they're watching the response. I was not asked to post my findings but your comments will be seen by those that care.

 

[davefr]

Who's the manufacturer?

Past posts indicate that BB kits have a somewhat tainted reputation in delivering any real gains. Is this one believed to be different?

P.S. Great images!!

 

[blsnelling]

I have only installed one BB kit in the past, an 066. It was a 2nd or 3rd gen kit. It was stronger out of the box than my ported 066 Red Light. I'm fixing to port another 1st gen 066 jug to put on a 064, so we'll see how it compares again.

Unfortuantely, I do not have a stock 7900 here to compare it to. If we have a GTG in the next couple of months, it should still be stock and we can compare them then.

 

[blsnelling]

Who's the manufacturer?

These are from Baileys as all of the BB kits are.

 

[Jacob J.]

Combustion chamber looks good- smaller than other big bore kits. Good job Bailey's.

 

[Saw Dr.]

Hmmm, Wasn't Brad looking for a 441? I wonder what else is in the works for a BB kit.....

 

[blsnelling]

Hmmm, Wasn't Brad looking for a 441? I wonder what else is in the works for a BB kit.....

There is a 441. I didn't take one since I wasn't real optimistic in scoring a cheap 441. If you have a beater to sell, I can get the kit and test it. That's the only other one.

 

[davefr]

These are from Baileys as all of the BB kits are.

Yes, but who's the actual manufacturer? Is it from a major manufacturer or some no name sweat shop in China?

 

[blsnelling]

Yes, but who's the actual manufacturer? Is it from a major manufacturer or some no name sweat shop in China?

I have no idea.

 

[Saw Dr.]

Yes, but who's the actual manufacturer? Is it from a major manufacturer or some no name sweat shop in China?

If it works well, what's the difference. People do it all of the time with cars, appliances, electronics, etc.....

Sorry, Brad. I'll quit bogging your thread down.

 

[Austin1]

These are prototypes for the purposes of evaluation. They will not be on the market for probably at least a couple more months.

That's great to hear, I don't think anyone could pull off a fair evaluation of a product more than you!I like reading your post as they are fair . +1 hope I have rep left.