What's on your bench today?

[wyk]

Wow. 390's have much tighter squish than most 372's. I had one at .019 after removing the base gasket.

[Eddy_t]

Wow. 390's have much tighter squish than most 372's. I had one at .019 after removing the base gasket.

 

 

Is the 385 as tight a squish?

 

 

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[spudulike]

Seal All 1: Rest of the engine 0

 

Seal all seemed to do the trick on the makita dbc410 crank seal spud but rest of engine [ATTACH]149598[/ATTACH]wouldnt hold pressure so removed from strimmer body.found another leak at the carb manifold- broken gasket. Lastly the whole bottom section of the engine(clam??) was leaking air.sealed it with some black rtv gasket maker.will retest tomorrow.

 

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Those clam engines need to be sealed from the cylinder base to the lower clam, high temp sealer is best. Gaskets can be made if necessary - done this many times!

 

Glad the seal-all worked out:thumbup:

[spudulike]

Wow. 390's have much tighter squish than most 372's. I had one at .019 after removing the base gasket.

 

It was really heavy with carbon, not just the normal black stuff but the light brown thicker crust as well. If you look at the pic of the side of the piston, you can see the build up on one edge,

 

All I can say is that the small bits that fell off the plug got lodged in this area and that stopped the machine turning over. I didnt use a wrench on it - was guessing something had come out of the exhaust and had entered the port and as I was pulling the cylinder off anyway, decided to go easy and investigate the problem before going any further.

 

All fine now and will fit a new plug after I have ported it:thumbup:

[wyk]

Is the 385 as tight a squish?

 

 

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They are similar. The biggest difference I noticed from a 385 to 390 was the port timing. Like they tailored the actual timing for less emissions VS simply leaning it out and stuffing the muffler. That's why many 385's standard run just as strong as 390's even though they give up some displacement to the 390. Having said that, some of the most impressive ported saws I have run were 390's with tight squish. If I were back in the PNW, I would definitely own another. Ported, they pull 32-36" bars with authority in Douglas Fir with skip chain, and oil them just fine.

[wyk]

It was really heavy with carbon, not just the normal black stuff but the light brown thicker crust as well. If you look at the pic of the side of the piston, you can see the build up on one edge,

 

All I can say is that the small bits that fell off the plug got lodged in this area and that stopped the machine turning over. I didnt use a wrench on it - was guessing something had come out of the exhaust and had entered the port and as I was pulling the cylinder off anyway, decided to go easy and investigate the problem before going any further.

 

All fine now and will fit a new plug after I have ported it:thumbup:

 

Hope ya didn't wrench too much on that upper AV mount. Looks like he got his saw stuck.

 

Here's some numbers I have from Parris and Brad in duration and degrees:

 

Ex- 170° duration, 95° ATDC

 

Int- 150 duration, 74° FTDC

 

Tran- 122° duration, 119° ATDC

 

My 390 was very similiar to yours.:

Ex-96

Tran-122

Int-76

Edited February 23, 2014 by wyk

[wyk]

Those are stock numbers, btw. Not ported. The exhaust is real high for stock on an 88cc saw. I would remove the gasket and not raise it any.

[predator]

i hope you dont mind me posting this here i just thought it would come in handy for all the diy/engineers looking in on this post some good info on there

 

Engineering ToolBox

[mikerecike]

Makita back together.fired up first pull.really chuffed-all down to everything i've learnt here about seals sealants, gaskets,pressure, vac testing....................and on and on..big cheers

 

Question. I replaced the ht lead which was too short.its one of those push into a spike in the coil collar jobs.ok if theres no tension on the lead but this is routed around a corner so naturally wants to pull out.i dropped a bit of spuds seal all across top to help anchor it.what else could be done?

 

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[Dan Forsh]

Makita back together.fired up first pull.really chuffed-all down to everything i've learnt here about seals sealants, gaskets,pressure, vac testing....................and on and on..big cheers

 

Question. I replaced the ht lead which was too short.its one of those push into a spike in the coil collar jobs.ok if theres no tension on the lead but this is routed around a corner so naturally wants to pull out.i dropped a bit of spuds seal all across top to help anchor it.what else could be done?[ATTACH]149678[/ATTACH]

 

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Are you sure it was push on? They are usually a self-tapping type screw in there so it should be twisted on.