''Spike Special' 372

[Kiwioilboiler]

As per title Gents, I am wondering the ease of replicating a Spike Special on my 2008 372 OE.

I don't have right angle porting equipment, but do have a straight air die grinder and various bits and stones.

It appears from the YT vids the idea is to lift the cylinder extension to unmask the transfer entrances.

Is anyone familiar with the procedure, specifically the type or name of the cutting tips required? Also, how much material should be removed?
It will be my first time grinding a cylinder and as it is a mint oe one I'm keen not to wreck it.

Cheers in advance for any advice.

 

[Spladle160]

It's not hard to get into the lower transfers with any old dremel or die grinder. Most burs will work, it's just aluminum. I don't know how much of a bump you'll really get just from removing the impeding portions of the cylinder extension but if you're going to delete or reduce you're base gasket anyways to optimize squish you may as well grind them while the cylinder is off. If you also advance you're timing and open up you're exhaust you've picked most of the low hanging power fruit. It's not a professional port job, but that's hard and takes skills and stuff. This is the cheap easy stuff that will make a noticeable difference.

 

[Ronie]

On mine, I matched the lowers with the gasket and cut the flange down almost even with the case.

 

[Kiwioilboiler]

Thanks @Spladle160 I'm all about 80% return for 20% of the effort so it sounds like just the ticket. Definitely basegasket remove anyway, and new cabers.

@Ronie that is beautiful work mate. No promises on my side....

 

[Lightning Performance]

Clean up any casting marks in your ports and knock off and high areas in your ports. Match your muffler to the port after you delete or drill out the muffler baffle. Go slow with a sanding roll and stay away from the wide parts except at the port window to the cylinder on the exhaust side. You can widen that a bit in most chainsaw motors.

I'm not very familiar with that model so I have little to offer but go slow.

 

[huskyboy]

Take a real real good look at a 385xp or 390xp cylinder and piston. Compare it to a 372xp. See what they did there from the factory? That was the inspiration behind this type of mod. Now there are many ways to skin a cat. The only way to find out what works for you is to test. If I were you I’d practice on a cheap cylinder or one that’s already junk first before grinding on an oem 372 cylinder if it’s your first time.

 

[Kiwioilboiler]

So i decided to try and understand a bit of this myself just now and applied torchlight thru the sparkplug hole and moved the piston down until a crack of torchlight was showing in the top of the transfer exit port. At this point the bottom of the oe piston and the cylinder extension on my oem Mahle cylinder were flush. Neither blocking the other. Checked it a couple of times, same result. In this case, how does knocking the cylinder extension 'up' help?
No pic sorry, i was out of hands already.

 

[Ronie]

My guess would be that it helps with a smoother flow into the lower transfers. I don't really know, I just followed what others have done.

@Spike60

 

[cus_deluxe]

In this case, how does knocking the cylinder extension 'up' help?

it helps more at the bottom of the stroke. ill bet theres a “witness mark” in that cylinder if its used, where you can see a shadow of where the piston stops at bdc. grind up closer to that

 

[Kiwioilboiler]

it helps more at the bottom of the stroke. ill bet theres a “witness mark” in that cylinder if its used, where you can see a shadow of where the piston stops at bdc. grind up closer to that[/QU

That's what I thought too, but at BDC it is the piston that is lowest. I'd have to take the piston skirt up..

 

[Ronie]

I wasn't sure what a Spike60 special was so I looked up a video of what he does. It looks like he lowers the floor of the intake .030, removes part of the skirt the skirt at the lower transfers and does a base gasket delete. That would be very easy to do. Here's the video I watched in case you haven't seen it. The last part of the video he explains what he does.

 

[Kiwioilboiler]

I wasn't sure what a Spike60 special was so I looked up a video of what he does. It looks like he lowers the floor of the intake .030, removes part of the skirt the skirt at the lower transfers and does a base gasket delete. That would be very easy to do. Here's the video I watched in case you haven't seen it. The last part of the video he explains what he does.

Ta, is that the one where Big Walt holds the cylinder just out of camera shot, coz if it is it's part of the reason I've taken to the typing here.

 

[Ronie]

Only thing I can add is after you grind on the intake is to bevel the edge so it doesn't scratch up the piston.

 

[cus_deluxe]

That's what I thought too, but at BDC it is the piston that is lowest. I'd have to take the piston skirt up..

i see now, i was thinking it was like a 346. same concept tho, as ronie said, to facilitate transfer flow

 

[huskyboy]

That's what I thought too, but at BDC it is the piston that is lowest. I'd have to take the piston skirt up..

Look at that part of the 372 skirt and look at the same area on a 385/390xp skirt.

 

[huskyboy]

I copied what they did on the 385/390xp cylinder and piston on a 365 special as well as gave it a woods port/popup piston. Turned out pretty good for basically an experiment out of curiosity. The saw seemed to gain a lot more torque and vibes were less from the lighter piston. Am I saying this is the right way to go? Nope. Many ways to skin a cat. That’s a 372 skirt I lowered but the 365 is the same.

 

[Kiwioilboiler]

Look at that part of the 372 skirt and look at the same area on a 385/390xp skirt.

Unfortunately i do not have access to any 385 parts at this time.

 

[Ronie]

Here's a pic of a 385 cylinder. There's a cut out of the flange at the lower transfers.