Has anybody put a de-comp on a 064

[Terry Syd]

I've got a mate who just had his 70th birthday. He's kinda, like, 'noticed' that he can't start his saw like he used to. I was wondering if anyone has put a compression release on an 064.

In the alternative, is there a coil, something like the 066 coil, that has a retard on starting?

I suppose I could just retard the ignition timing a bit (I'm leaning this way).

I agreed to fix his saw for his 70th birthday. The coil has apparently gone, so a replacement with a retard would be a great option.

He likes the idea of a compression release, so if anyone has done it, please let me know.

 

[jacob j.]

I think you'd have to do it near the top of the combustion chamber, and then cut a hole for it through the top cover.

You could fit a a thicker base gasket along with some timing retard and that would help. I did that for an older gentleman who had an 046 he could no longer start.

One of those slimmer McCulloch-style compression releases might be better since they make a smaller hole and don't need as much material to seat in.

 

[treesmith]

Pretty sure the cross cylinder has a decomp, not oem but mine runs nice stock

 

[Yukon Stihl]

066/660 cylinder with a decomp would be another option

 

[Dub11]

Did @drf256 do a build like this ?

 

[dustinwilt68]

The MS650 cylinder is the later 064 with a decomp built in, it's one reason people love them for porting, they also have a thick base.

 

[Terry Syd]

Thanks for the heads-up guys. I just checked the Cross BB (54mm - 91.6cc) and it does have a de-comp hole. What is the stock displacement on a 064?

I might be able to convince him to go with a Cross BB and then retard the ignition timing a tad. He's only running a 20" bar with an 8-pin, so 92cc should pull it fine even if I retard the ignition 4 degrees.

Sure wish there was a coil with a retard on starting like the 066 coil. That works just great for a number of saws.

 

[dustinwilt68]

85cc for a stock 064, with the cross just make sure and check the lower lips on the intake and exhaust they have been known to forget to bevel the edges from the facotory and use a meteor 066 piston.

 

[drf256]

I've got a mate who just had his 70th birthday. He's kinda, like, 'noticed' that he can't start his saw like he used to. I was wondering if anyone has put a compression release on an 064.

In the alternative, is there a coil, something like the 066 coil, that has a retard on starting?

I suppose I could just retard the ignition timing a bit (I'm leaning this way).

I agreed to fix his saw for his 70th birthday. The coil has apparently gone, so a replacement with a retard would be a great option.

He likes the idea of a compression release, so if anyone has done it, please let me know.

Terry,

One could make a small vertical relief in the center of the plating by the Ex roof. Like a 10* relief. That would effectively act as a decomp at low rpm, but not affect high rpm power. Kinda a hybrid of the old McCulloch T slot port. All of the relief inside the jug so it can’t be seen from outside. Like 2mm wide, 10* high, and angled down so that it is shallowest towards the chamber and deeper by the ex port. I’d help ya with it, if I wasn’t half way around the world. I still would, but shipping wouldn’t be worth it.

There are AM 064 ports available. JMS built one for Jchin. He said it was “the best 064 cylinder I’ve ever seen”-for what that’s worth.

If you go with the 54mm bore jug, I believe you need M6 case bolts, not the M5 that came with the 064 (so I’ve read).

Ive never added a decomp to a non decomp cylinder.

 

[Deets066]

Doc is right, slot in the ex. Port would be my vote. Back the timing off a fuzz like you said, and maybe add a D starter handle. Much easier on the hand

 

[Terry Syd]

Hmm, sounds like a cheap option. I could put a notch in the top of the exhaust port. I've seen that before, never done it. My lawn mower has such a notch, but I expect that is for noise, it drops the pressure before the main port opens and reduces the magnitude of the exhaust wave. I think the bottom of the notch and thus the main exhaust port is even with the transfers opening.

It would loose a bit of power as the pressure differential is higher when the port first cracks open, but it could work. If I backed off the ignition timing a bit, then he might have an easier starting 064. He doesn't need all the extra power that a pumped up BB jug could give him, especially using a 20" bar.

I'll run that option past him first and then if he wants the BB jug with the de-comp. It will be his money. Thanks for the idea.

 

[Deets066]

This may be a stupid question.... but if he’s only using a 20” bar. Why not use a smaller, easier starting saw?

 

[Deets066]

An 064 is a lot of things, but never heard them described as easy starting

 

[Terry Syd]

It's 'his' saw, he's been using it for years. I agree about getting a smaller saw, but the only reason he is using the 20" bar is that I gave that bar to him. Before that he was running a 24" bar on the machine. - The size of the wood he cuts he could be using an 18" bar.

I hate the saw, I've had to start the thing several times for him. Oh, and I also showed him how to sharpen a chain, which from looking at the chain, he hasn't quite mastered.

I expect that I will have to completely rebuild the saw. Besides the coil, there's something wrong with the clutch. I'm going to fix it up for his 70th birthday gift - but after that, I never want to see the thing again.

I only recently got my bench cleared of junk, now I'm going to have his saw taking up all the space.

 

[Terry Syd]

And just to add insult to injury, he didn't even have the decency to clean the POS. It is absolutely filthy, baked on grime from years of use.

The local community knows that I can fix chainsaws, so people are always showing up and asking me to 'just take a look at it'. Yeah, sure, just take a LOOK at it.

After fixing the Fire Brigade's saw (and never got a thanks), I swore I was never going to do something like this again, but it was his birthday. I usually end up using some of my available parts and my money as most of them are doing it fairly hard. I fully expect to hear a grumble when I mention the costs associated with this build. "Just do it on the cheap" - well, no, it NEEDS a carb kit and a fuel hose and a ......

I expect a lot of you guys have been through the same thing - just having a rant..

 

[Terry Syd]

I just had an idea. Instead of notching the cylinder, why not take a needle file and notch the top of the piston. Admittedly it would raise a potential hot spot, but this guy doesn't run the saw hard enough to worry about it.

The notch on the front of piston would allow the saw to vent some mixture while starting, but the top ring would still be sealing while under power. It would probably have less an effect on the power. - It would also be easier to do as I wouldn't have to remove the jug.

Anybody ever do something like this?

 

[MustangMike]

I have used the Cross P+C on several 066/660s and like them, but I fully agree to check the port bevels, especially the ones you can't see. They generally result in a saw that is not too hard to pull over even with a base gasket delete. With a base gasket, they should be a dream!

I'm sure the Meteor is a better piston, but I have not had any issues with the Cross ones, and they come with Caber rings. I also heard the Meteor 660s have a bit less squish than the Cross pistons, so check it if you use one.

And, another possible solution, a thicker base gasket.

Good Luck with it. I have had my 044 since new in Dec 92, and will never sell it, so I understand his attachment to his saw. Plus, I'm only 4 years behind him!

 

[MustangMike]

Not a bad idea, but I don't think I would file a piston w/o removing the jug, unless, you pressurize the chamber through the spark plug hole.

 

[Terry Syd]

I've filed the top of the piston through the exhaust port before when shaping the top of the crown to the top of the exhaust port. It is a mod that gives you the equivalent of about 2 degrees extra blowdown without raising the exhaust port. It is a pain to do correctly as you have to keep checking with a light through the spark plug hole to monitor the shape as you proceed. That mod creates a nice curve on the piston crown and doesn't create a hot spot like a notch would in the middle of the piston.

Notching the piston is at least a reversible mod with a new piston, if I notch the cylinder it is going to stay notched.

If it was my saw I'd definitely go for the 92cc Cross cylinder, but I can already hear the word "cheap" coming out of his mouth. The Australian dollar exchange rate puts the Cross cylinder up around A$200, and that's without postage to Oz.

I wish I had a working compression gauge. It would be interesting to see how much the notch drops the starting compression. The gauge could also tell me how much I needed for the mod to be effective. I'll just have to wing it...

 

[drf256]

I just had an idea. Instead of notching the cylinder, why not take a needle file and notch the top of the piston. Admittedly it would raise a potential hot spot, but this guy doesn't run the saw hard enough to worry about it.

The notch on the front of piston would allow the saw to vent some mixture while starting, but the top ring would still be sealing while under power. It would probably have less an effect on the power. - It would also be easier to do as I wouldn't have to remove the jug.

Anybody ever do something like this?

Not a bad idea, at all.

I’m not sure that there is enough room there, above the top ring, to make the difference. Perhaps there is.

Go on Torquesoft Software, see what difference the size of the notch you can fit will make, and try.

I’m worried that the notch will affect piston strength, be a stress riser, and crack.

I also wouldn’t file anything in a cylinder without it being diassembled so it can be fully cleaned afterwards.