Degreed my saw, now what?

[Four Paws]

I degreed my stock Shindaiwa 757 without the base gasket (.019" compressed) installed. The squish measured at .052" (huge, I know). The port timing is as follows, all measurements are ATDC:

Intake
Opens:277
Closes:78.5
Duration:161.5

Exhaust
Opens:96
Closes:259.6
Duration:163.6

X-fers
Opens:126.5
Closes:233.5
Duration:107

So, what do you guys think of the stock numbers? I have heard various timing figures from some of you, different theories, etc. If I milled .049" off the cylinder to get my squish set at .022" (decent and safe for a work saw) with a base gasket installed, I would obviously shift the port timing some.

The ports are about as wide as I should go on the exhaust side, I could take them about 1/32" wider on each side of the intake. Just want to make sure I leave adequate support for the piston and rings.

 

[ShoerFast]

Measure twice, cut once!

You need to cut .03 to get your .022 (from .052)

 

[Cut4fun]

I would like to see the pics you were talking about posting on HS. The inside of the cylinder if you can. I cant help on the numbers, I am dummy and scaredy cat to try a porting, I leave that stuff up to them smart fellers in the know. Sure feels good to run one of those hot woods ported saws though. I will stick to that end of it. Good luck and post pics, I do like to check out the work etc.

 

[Four Paws]

Measure twice, cut once!

You need to cut .03 to get your .022 (from .052)

Yes, you are correct if I wasn't going to run a base gasket. But, I prefer to run a gasket than use a gasket sealer, so .049" it is. I appreciate you looking out for me though!

 

[Four Paws]

Here are the pictures of the cylinder. Do you think the cumbustion chamber is too small for a .022" squish? I don't want to end up with over 200PSI cranking compression. WIth the base gasket installed (squish of .071") the saw pulls over at 148psi. It would be great if I could get it to end up at around 190 PSI cranking compression.

Intake:

Exhaust:

Transfers:

 

[Cut4fun]

From what I hear, thats all the better. But what do i know, not much.

 

[Lakeside53]

Yes, you are correct if I wasn't going to run a base gasket. But, I prefer to run a gasket than use a gasket sealer, so .049" it is. I appreciate you looking out for me though!

One reason to not to use a standard paper a gasket is that it will get packed over time by the high compression cycles, or, the cylinder mounts can stress crack.

You may not get optimal compression anyhow - cylinder looks a bit scruffy!

 

[Four Paws]

One reason to not to use a standard paper a gasket is that it will get packed over time by the high compression cycles, or, the cylinder mounts can stress crack.

You may not get optimal compression anyhow - cylinder looks a bit scruffy!

Yeah, the cylinder was covered in aluminum from the melted piston. This is a low budget, learning experience...not a competitive race saw, or money making work saw. I am attempting to simply teach myself a new skill, have fun doing it, and maybe end up with a saw that will perform better than stock. I wouldn't try porting a brand new $200 cylinder...but a scruffy one is just fine for this project!

 

[Lakeside53]

I'm with you on that.

I'm waiting for someone else to port their shiney new 441 first. Heck, someone has to be first, but it doesn't have to be me.:biggrinbounce2:

 

[Four Paws]

The decision process

Having had the pleasure of discussing my project with some knowledgable folks who were quite happy to offer up some words of advice (THANKS) I have a formulated a game plan. I am stopping by my buddies house tomorrow after work. We are going to look at getting the cylinder chucked up in his lathe. Might end up building a fixture to hold it securely.

I am going to shoot for .025" squish and cut the cylinder base accordingly. After the machine work is done, I will degree the saw again. I will then adjust my exhaust and my transfers back to stock open timing. I will also increase my duration on the intake timing, and widen both the intake and exhaust ports some.

I will post picture updates as I progress, and if this thing runs - LOL - I will eventually post cutting times!

 

[MacDaddy]

Some shindiawa saws have rev limiters and people lean the carb tring to get it to rev and thats why they tend to melt pistons. I would posibly change out the ignition if you want it to run up high

 

[buck futter]

can you take a picture of the piston and post it. How did you get your degree numbers? Will any more of the scuffing on the exhaust side clean up?

buck

 

[buck futter]

I don't know the full scope of the plan that have been passed to you. here is my take your open and close numbers should be the same right? when I calculate your open and close of your exhaust I come up with 100atdc from the numbers you have given.

1. cut your squish first

2. re degree it I think the biggest impact will be on the exhaust and intake. I would not touch the bottom of your intake just widen and raise what you can. You are advancing it by dropping the jug

3.the transfers you may want to widen to the back (closer to the intake). the piston ring locating pin play into this because if it is off set from centerline the transfers can grab the ring if you widen to much. try not to touch the top unless it is unavoidable. You also may want to polish up the bottom some.

4.as it sits now I think you need to raise the exhaust at least 4 degrees but 6 wouldn't hurt. Widen what you can and really pay attention to your port edge chamfers. Chamfers also count for your port timing so watch it.

 

[Cut4fun]

info

Buck futter go over to hotsaws and you will find 7 pages of builders talking about this over there. alot of good info for you porters on this same post on hotsaws.

 

[blis]

one idea worth of thinking when planning on porting, is to drill holes to sides of exhaus instead of widening them... makes those rings last alot longer and also decrease the risk of jamming the rings into exhaust...

 

[Crofter]

Blis, it sounds like some tricky drilling. Careful you dont make daylight where you dont want it or get the span of the holes wider than the piston skirt will cover or your saw will get a bad case of the hiccoughs!

 

[Four Paws]

I don't know the full scope of the plan that have been passed to you. here is my take your open and close numbers should be the same right? when I calculate your open and close of your exhaust I come up with 100atdc from the numbers you have given.

I don't really follow you here...what exactly are you asking? What are you calculating exhaust timing for, I have already measured it (stock head, no gasket).

1. cut your squish first.

Had the cylinder over to my buddies house tonight. We did more BSing than working, and we both have to be up early for a 12 hr. shift tomorrow. Anyhow, looking like we will find time to get the tapered wood spindle made and the cylinder turned this week.

2. re degree it I think the biggest impact will be on the exhaust and intake. I would not touch the bottom of your intake just widen and raise what you can. You are advancing it by dropping the jug.

True. I will assemble it after the machine work is done, and then degree it again. I will get the timing numbers and go from there. I will widen the intake and exhaust ports some.

3.the transfers you may want to widen to the back (closer to the intake). the piston ring locating pin play into this because if it is off set from centerline the transfers can grab the ring if you widen to much. try not to touch the top unless it is unavoidable. You also may want to polish up the bottom some..

Great advice...several others have made the same comment about leaving the upper transfers alone and working the bottom transfers over - smoothing and polishing some.

4.as it sits now I think you need to raise the exhaust at least 4 degrees but 6 wouldn't hurt. Widen what you can and really pay attention to your port edge chamfers. Chamfers also count for your port timing so watch it.

Your thoughts on the exhaust are also very consistent with other advice I have received. Great imput Buck! Thanks for posting and sharing your knowledge! Hopefully after all is said and done, the help I have received from others will allow me to build a sound saw, and by documenting it here, some others will take a chance at it.

Josh

 

[Four Paws]

one idea worth of thinking when planning on porting, is to drill holes to sides of exhaus instead of widening them... makes those rings last alot longer and also decrease the risk of jamming the rings into exhaust...

blis, this seems to work better on larger engines - BIG cc sleds and bikes. I have also seen where guys widen the ports so much that they build a bridge in the middle to support the ring (race sleds). That is taking it beyond what I am trying to accomplish. Thanks for the input though.

 

[Four Paws]

Back at it - Machine work complete!

Hey, I wanted to send out an update - I have the machine work on the cylinder completed and have degreed the saw to find out my starting point for porting.

Squish is now .024"

Int O = 278.1* ATDC
Int C = 84.7* ATDC
Duration = 166.6*

Xfer O = 121.8* ATDC
Xfer C = 237.6* ATDC
Duration = 115.8*
(I have figured out a better, more accurate way of measuring the X-fer port open and close times, hence the longer duration that previously posted)

Exh O = 100.5* ATDC
Exh C = 261.7* ATDC
Duration = 161.2*

Blowdown is 21.3*

As you can see, the intake is looking pretty good - just a little clean-up and it should be good to go. The exhaust needs the most work to get the blowdown where it should be. I am going to leave the transfers alone for now, just clean up the lower transfers and blend them slightly like the pictures Dennis posted of his 460BB (hotsaws.com).

So far, this has been a really rewarding process. I unfortunately didn't snap any pictures of the cylinder chucked up on the lathe - but it worked out smooth! I will keep posting updates as I go - and hopefully this write-up will encourage at least 1 person to port their saw, or at least drop $40 on a used Wildthingie and give it a go.

SO - comments, advice, critiscism - let's hear it all!

Josh

 

[Four Paws]

I like seeing pictures just as much as the next guy, so here ya go. Got the intake widened and cleaned up, and one transfer port done this afternoon.