372 xp first ever porting rebuild

[Chesterewers]

Hi I am in the middle of porting a 372 xp replaced the cylinder and piston with xpw I stayed far away from the 52mm aftermarket after reading some bad reviews about them. Maybe they are not so bad? but every blue chop saw I see dies after a few days on the job site, don't know where they are made just a off brand, someone knows of them? Well I just know when quality production is in place things last longer cheaper isn't always better. So Oem 372xpw cylinder piston for my burnt out 372 saw. I am porting it will post pictures, and checked timing durations today, I had 152 ex, 160 intake, I was told the intake is fine exhaust may need to be raised, I already raised it a little to get the current number but was also told that 372xp's have low compression anyway and not to touch exhaust timing. I think after hearing that I am fine with the numbers put it back together and run it, good enough. So let me know if its okay or not on the numbers?

 

[parrisw]

I still kinda think that 152 on the ex is low considering you raised it? But maybe you didn't raise as much as you think you did. Maybe post your process of how you came up with the numbers, when I do it, I check duration, then with a simple math you can get timing, I then, also set to TDC then find timing that way, and compare numbers from the first time.

When checking duration, I shine a small pen light through the plug hole, then just as you see the ex crack open, you can see the light, zero the degree wheel, turn now so the port opens then all the way around back until the light just disappears, check your number.

 

[tlandrum]

my 372xp with no popup has 145psi and is running at 161 on the exhaust. id get that exhaust up to atleast match the intake number. it should still have good torque. ive been running a 24'' bar and full comp chain on mine with no problems

 

[parrisw]

my 372xp with no popup has 145psi and is running at 161 on the exhaust. id get that exhaust up to atleast match the intake number. it should still have good torque. ive been running a 24'' bar and full comp chain on mine with no problems

I agree that your ex is low. But just make dam sure you got that number right!!!! Other wise you'll have a nice looking paper weight.

 

[Chesterewers]

I agree that your ex is low. But just make dam sure you got that number right!!!! Other wise you'll have a nice looking paper weight.

Your right I could be wrong, altho I read it off the degree wheel several times, its my first time reading the degree wheel, I think after cleaning the cylinder I'l recheck it again I don't know how it could be so far off, I will measure again compared to oem last time I measured it was.60'' difference from what I filed away. So really I shouldn't have a problem but the degree wheel says I do but it could be human reading error on my part. Best to be cautious as stated dont want a paper weight.

 

[tlandrum]

are you measuring the oem 372 as compared to the 375 cylinder. that may be why there is a difference. my xpw was somewhat ported when i got it so i dont know what stock numbers on the 375 were

 

[Chesterewers]

are you measuring the oem 372 as compared to the 375 cylinder. that may be why there is a difference. my xpw was somewhat ported when i got it so i dont know what stock numbers on the 375 were

Both cylinders are oem 372xpw measure take the differnce. I'll check everything again, and if no one has any reason why it won't run I will try it? Like someone said if I take too much off its a paperweight, in that case if it don't work right I can always take apart and file more for the proper numbers? Or just do it right to start with? I don't know I took a bit much off already and was worried.

 

[tlandrum]

definately dont take anymore off the bottom of the intake

 

[komatsuvarna]

I still kinda think that 152 on the ex is low considering you raised it? But maybe you didn't raise as much as you think you did. Maybe post your process of how you came up with the numbers, when I do it, I check duration, then with a simple math you can get timing, I then, also set to TDC then find timing that way, and compare numbers from the first time.

When checking duration, I shine a small pen light through the plug hole, then just as you see the ex crack open, you can see the light, zero the degree wheel, turn now so the port opens then all the way around back until the light just disappears, check your number.

+1 Thats the way I do as well. I like to check and then recheck myself. If the numbers come out, then you know your right.

 

[Chesterewers]

+1 Thats the way I do as well. I like to check and then recheck myself. If the numbers come out, then you know your right.

yes I think your right, I measured again the stock compared to my ported and triple checked it I only filed away .013''

 

[Chesterewers]

yes I think your right, I measured again the stock compared to my ported and triple checked it I only filed away .013''

I filed a little more now difference is .021.5 my guess is that should probably get me where I need to be.

 

[tlandrum]

put it together and check with a degree wheel,dont be guessing

 

[Chesterewers]

images of port job

here are some images of what I have done so far

 

[komatsuvarna]

put it together and check with a degree wheel,dont be guessing

+1. It takes about 5 minutes to put the cylinder back on and check the timing again......and forget that other cylinder. Dont be measuring your ports off of the other cylinders ports. If you go to far you'll end up with a screaming saw that wont cut a butter biscuit.

 

[komatsuvarna]

Something else that might help ya is do one part at a time. Im no expert and dont know how other people do it, but I like to start and finish one part at a time....Instead of grinding here for a minute,,,, and then moving here,,, and then lets go to the transfers a minute,,,,alright Im done,,,on no I forgot to finish the intake,,, and forgot one of the upper transfers. Kinda like most other things, start at one end and go to the other. Thats just what works better for me though.

 

[Chesterewers]

Another good question I never even asked is on the crankcase is it normal to have oil on the crankshaft and in that case? If not than I would assume the oil is getting in there through the seal and I would have to split the case, if so than I will guess a vac test will work fine to just check it. I don't own a vac test but from what I read I would just buy a mighty vac duct tape off intake exhaust and then run the test, is there any eaisier way to test it or is that it? Thanks.

 

[RiverRat2]

?????

R U kidding????? just picking I guess if youve never been in one this deep you wouldnt know, please pardon my skewed sense of Humor,,,,, it is Monday,, and I wasnt thinking!!!!

You R talking about 2 stroke oil right,,, not bar oil???

There better be some 2 stroke oil in there,,,,, it comes out of the fuel/mix and should have a good film on all the rotating parts,,, and perhaps a bit of residue on the crankcase walls and some down in the bottom is typical,,,,

 

[gink595]

Another good question I never even asked is on the crankcase is it normal to have oil on the crankshaft and in that case? If not than I would assume the oil is getting in there through the seal and I would have to split the case, if so than I will guess a vac test will work fine to just check it. I don't own a vac test but from what I read I would just buy a mighty vac duct tape off intake exhaust and then run the test, is there any eaisier way to test it or is that it? Thanks.

It would be "Un-normal" if you didn't

 

[Chesterewers]

ok

R U kidding????? just picking I guess if youve never been in one this deep you wouldnt know, please pardon my skewed sense of Humor,,,,, it is Monday,, and I wasnt thinking!!!!

You R talking about 2 stroke oil right,,, not bar oil???

There better be some 2 stroke oil in there,,,,, it comes out of the fuel/mix and should have a good film on all the rotating parts,,, and perhaps a bit of residue on the crankcase walls and some down in the bottom is typical,,,,

well I kinda figured so since the bearings are there but just wanted to be certain, most my work has been on 4 stroke engines sorry. Thanks friends

 

[Chesterewers]

well I kinda figured so since the bearings are there but just wanted to be certain, most my work has been on 4 stroke engines sorry. Thanks friends

Its running now, I am still adjusting the carb, I tested the compression its at 150psi I think most people do a little better than that but that isn't bad I think. Maybe average?