McCulloch Chain Saws

[heimannm]

Joey was using a Grabit available at Lowes and other similar stores. https://www.lowes.com/pd/GRABIT-Grabit-1/3073145

The rings used in the late model 7-10 and PM700 saws are thin rings, so made from steel with no taper and no chrome ring for the top.

Mark

 

[joeymt33]

Thanks a ton for that demonstration. Helps a lot in understanding what's involved. What size 'easy out' did you end up using? Certainly looks like the way to go to salvage this style cap.

I was using a #3 size.

 

[PogoInTheWoods]

Thanks guys.

I found one that seems to fit. One down so far. The second one is being pretty stubborn, tho. Older style easy out with a square shank end that won't fit in my smaller Bosch 1/4" hex drive impact unit (great little impact for saw work, btw.) and just loosens the chuck on my 3/8" DeWalt. The Grabit or some type of 1/4" hex shank extractor may be a better way to go as I think the impact aspect is the ticket on these.

​

And on my SP81 rings, they're thin rings too. I see em on eBay in the $25 range. But again, I haven't found conclusive specs on end gap so don't really know how far gone mine actually are. Trying to do a compression test with a drill proved to be a fruitless exercise..., at least in my particular case. I'd go ahead and buy rings but am a little concerned about a vertical gouge in the cylinder that may render new rings moot anyway, though the piston itself is in fairly good shape and would probably benefit from them in a new cylinder somewhere down the road. Just not sure which way to go on that at this point.

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I sure do appreciate the help, fellas. Thanks again.

 

[PogoInTheWoods]

Yay. I managed to get all three apart without breaking the caps. (The one on the left already had the broken threads.) Had to use Cory's approach on the second one and the third was a brass one that just twisted out as Mark said it should. I gather the brass version innards consist only of the spring and a duckbill? That's all that came out of it. No 'o' ring or nylon piece..., but a gob o' goo.

​

 

[heimannm]

There is supposed to be a kind of brass washer/bushing that fits the end of the spring and the flange of the duckbill, but I find they are often missing.



Now we need some creative fellow with a lathe to start making new inserts to press back into those fuel caps with the (aluminum?) fitting. Where to find some small diameter aluminum rod??

Many will say 0.0015 to 0.002" of gap per 1" of bore, in your case 0.003 to 0.004" would be minimum with a 2" bore. 0.005 to 0.006 would still be quite acceptable but over that will start to affect the compression. That said, many a saw will have a lot more end gap on the rings and still run.

Mark

 

[PogoInTheWoods]

If this is the correct orientation for the duckbill, a Homelite/Stens 69451/610-345 seems to fit. Not sure how just the spring and brass insert will keep it in place, tho. Any chance you may have a better illustration than the manual (or a link to one) for how these various vents go together?

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And my ring end gap isn't anywhere close to the tolerances you suggested. I'm just going to order rings to at least give the piston a fighting chance in the existing cylinder.
Set #87854 I presume?

 

[fossil]

And my ring end gap isn't anywhere close to the tolerances you suggested. I'm just going to order rings to at least give the piston a fighting chance in the existing cylinder.
Set #87854 I presume?

Don't forget to take the locating pin in the ring groove in you calculations. The ring ends will bind once they make contact with the pins.

How far up does that gouge in the cylinder go? One of my 3400's has a deep gouge in the cylinder above the exhaust port and is the strongest runner in the few I have.
You might be surprised.

 

[acpat]

anyone got a trick to getting the decomp valve to work. guy I got saw from never used it and ran saw rich. I tried the wooden dowel but am leery of getting violent with it. I think it is plugged solid :-(
pm 850.

 

[fossil]

In case no one else chimes in to the contrary, I've found Hoppes No. 9 powder solvent to be good for removing carbon. Remove the decomp and use that and a brass brush to get the carbon out.

 

[PogoInTheWoods]

Don't forget to take the locating pin in the ring groove in you calculations. The ring ends will bind once they make contact with the pins.

How far up does that gouge in the cylinder go? One of my 3400's has a deep gouge in the cylinder above the exhaust port and is the strongest runner in the few I have.
You might be surprised.

There's plenty of room for the locating pins as it is now. Trust me. I would assume a new set of OEM rings would take them into consideration as well. But if I need to file em, so be it.

As for the gouge, it runs a fair distance from below to above the ports with a couple of very minor adjacent ones..., all of which combined don't equal half of my existing end gap! LOL

I'm probably making way too much of it but want this saw to be as right as it can be within reasonable financial limits. Gotta save my pennies for that elusive PM8200 piston, ya know?

I'll post a pic of the cylinder.

 

[fossil]

Anything below the ports doesn't do squat to the compression. As long as there are no raised edges I would doubt it would do anything bad for the amount you are likely to run it. I know that stuff bugs me though. My memory is not too good anymore so it's minor for me.

 

[PogoInTheWoods]

Well, I plan on runnin' it..., a lot! And I don't worry much about what's below the ports either unless there's plating deterioration that looks progressive enough to possibly cause piston damage by additional flaking.

So anyway, here are my gouges and my end gap. Gouges don't look so bad now. End gap still does!

​

 

[joeymt33]

That ring gap does look excessive. And for the marks on the cylinder wall, I don't think that's enough to worry about.

I say put that thing together and let her eat!

 

[fossil]

Looks darn near perfect for an old Mac.

 

[PogoInTheWoods]

'Preciate the encouragement. Glad I revisited both issues here with you guys before committing to more assembly. Now to shop for some rings. Are Cabers available for Macs or is it pretty much OEM only?

 

[Brian Thacker]

anyone got a trick to getting the decomp valve to work. guy I got saw from never used it and ran saw rich. I tried the wooden dowel but am leery of getting violent with it. I think it is plugged solid :-(
pm 850.

Usually their is a cleanout plug somewhere around the DSP valve. It is usually a cap screw. Remove it and be very careful. I used a drill bit on my PM 55 the other day to clean it out. I started with a small drill bit, not in a drill, just by hand and worked my way up until I got it clean. You could feel the drill bit hit metal when you get big enough.

Brian

 

[heimannm]

acpat - As Brian said, there is an 10-24 socket head cap screw that plugs the cross drill into the cylinder. This screw is very obvious in post 25598 and missing from the saw in post 25600. Use a 5/32" drill bit by hand and work the port open.

Poge - the assembly order for the fuel cap with the plastic insert (same as brass insert) is shown below. I will try to remember to push a set of NOS rings in a NOS cylinder tonight and check the end gap, that should be a 100% answer to your question. I don't know if Caber makes thin steel rings like those used in the SP80/81 saws. There is an e-bay seller located in Canada but ships regularly from Buffalo, NY that usually has rings for the more popular McCulloch engines with reasonable prices or get a complete new piston with rings and bearings from customchainsawparts for $45 + shipping.



Mark

 

[acpat]

got decomp cleaned out with hoppes #9 and wooden dowel. works good now. Installed new fuel line and it leaks worse than the old one I took off. plus in middle of all this the spark plug threads came out with the plug !!!!! one step forward two steps back.
1. how do you get fuel line to seal to tank or who makes a good one that has correct O.D. so it seals ?
2. who makes tool to rethread/helicoil spark plug ?

 

[fossil]

For the fuel line, wrap some plumber's teflon tape around the fuel line where it passes through the tank. Works great.

 

[Brian Thacker]

I have used the plumbers tape several times and works well. To repair the spark plug hole I like time-serts better than heli-coils. They are more expensive but well worth the extra cost.
I usually get them off Amazon.

http://www.timesert.com/

https://www.amazon.com/dp/B00J9PJOUY/ref=sr_1_1?m=A2N5EWWITZXTMB

https://www.amazon.com/dp/B0025NL1V2/ref=aag_m_pw_dp?ie=UTF8&m=A2J41G0RQ2IUXB

Brian