Author Topic: Deck Height Difference in XT Cases Versus XP Cases  (Read 829 times)

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Offline KilliansRedLeo

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Deck Height Difference in XT Cases Versus XP Cases
« on: May 05, 2014, 05:28:21 pm »
There was a thread up here somewhere where Spike60 made mention of a potential difference in deck height between a set of 372XP carankcase and an 372XT crankcase. Well I cannot find it. What Spike60 mentioned was that you could put an XP top end on the XT cases but not the opposite. Inferring that the XT case had a higher deck than the XP crankcase. Does anyone know if there actually is a difference.

Here is the reason I ask. Weimedog and I are toying around with using a 272XP piston in a 372BB kit. The 272 piston is shorter overall but quite a bit taller in compression height than the stock 372XP piston. Talking to Weimedog we were thinking that we might be able to use a 272XP piston in the BB kit and get two advantages out of the piston. Increased compression because of the increase in Compression Height and a change in intake timing because of the shorter overall height. The only problem with this train of thought is that because of the difference in compression height you would have to use two or more base gaskets.

However if the deck height of the 372XT is truely higher than the 372XP them perhaps one could get away with a single base gasket or no base gasket. If anyone knows the answer to this let me know. I have 372XP cases floating around and already know you cannot put the 272XP piston in the saw using a pair of XP cases without using three standard base gaskets. However I do not have a set of XT cases to try, so am asking the questions to avoid buying a set of XT cases.

Here are the specs from Meteor on the stock 372XP piston

Brand HUSQVARNA
Motor Chainsaw mod. 371 - 372 XP
Piston 1725
Diam 50.00
Compression 22.50
Head P
Length 42.50
Pin 12 X 36 X 8

Here are the specs from Meteor on the stock 272XP piston

Brand HUSQVARNA
Piston 2061
Diam 52.00
Compression 24.00
Head P
Length 40.50
Pin 12 X 33 X 8
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Offline KilliansRedLeo

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From looking at IPLs it appears that at one time there MAY have been a different case used on the 372XT. The earliest IPL I could find lists a different CC part number for the XT than the XP. See below, the first entry is from the earliest IPL for the XT the second and third parts are for the later XT and the XP, which show the same part number.

Husqvarna 503626808 (replaces 503626876) RP CRANKCASE

Husqvarna 503626808 CRANKCASE ASSY

Husqvarna 503626808 CRANKCASE ASSY

It also appears that the XT C/P kit has changed part numbers, see below perhaps indicating a change

 Husqvarna 575255702 (replaces 575255701) RP CYLINDER ASSY

Husqvarna 575255702 CYLINDER ASSY

I cannot find an IPL for the 365XT so perhaps the earliest IPL was actually for the 365XT!
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Offline 660magnum

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Troll brought up the fact a while back, that  IPL's, replacement OEM, & "as built" may not match?

I was messing with a 111 Dolmar and if you've seen several different years of these, you have noticed differences. You can see this on the IPL's if you have the real examples to help you out. You certainly can not go by what the sellers on Ebay say!

The 371 cylinder and clutch bell are different from the the 372. Either part will fit either saw but they are different.
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Offline Reddog

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Here was the info.

I've never had the need to mess with one of those impulse pipes myself. But you'd think that there would be instances where someone might need to order that as a spare part.

One thing to add here regarding cases is that there is a difference between the originals vs the new X-torq models. The skirt on the bottom of the XT cylinders is deeper than the originals, so the corresponding cut in the XT cases is also deeper. If putting an original jug on an XT case, you will have no problem. But you cannot put an XT cylinder on the original case. (unless you do some grinding) As far as deck height, I really can't say.
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Offline KilliansRedLeo

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Thank you Reddog! What I was thinking was that if the deck height was higher in the XT case that might allow the use of the 272 piston without the need for a stack of base gaskets. Oh well, perhaps a spacer out of copper shim stock.
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Offline SawTroll

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Here was the info.

I've never had the need to mess with one of those impulse pipes myself. But you'd think that there would be instances where someone might need to order that as a spare part.

One thing to add here regarding cases is that there is a difference between the originals vs the new X-torq models. The skirt on the bottom of the XT cylinders is deeper than the originals, so the corresponding cut in the XT cases is also deeper. If putting an original jug on an XT case, you will have no problem. But you cannot put an XT cylinder on the original case. (unless you do some grinding) As far as deck height, I really can't say.

That isn't about deck height, as I read it, but about the cutouts for the cylinder "skirt" (going below deck height).

Offline farmboy

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I cannot find an IPL for the 365XT so perhaps the earliest IPL was actually for the 365XT!
I couldn't find one either.  Although I haven't looked on HVA manuals.  I use the 372XT IPL.  The starter cover decal and the transfer covers are the only difference.
Here was the info.

I've never had the need to mess with one of those impulse pipes myself. But you'd think that there would be instances where someone might need to order that as a spare part.

One thing to add here regarding cases is that there is a difference between the originals vs the new X-torq models. The skirt on the bottom of the XT cylinders is deeper than the originals, so the corresponding cut in the XT cases is also deeper. If putting an original jug on an XT case, you will have no problem. But you cannot put an XT cylinder on the original case. (unless you do some grinding) As far as deck height, I really can't say.

That isn't about deck height, as I read it, but about the cutouts for the cylinder "skirt" (going below deck height).
That is the difference.  Cylinder skirts are longer on XT cyl.  I use a reg 372XP CC for case matching.
Shep

Offline KilliansRedLeo

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Spike does mention deck height, that is what I remembered but he says that he doesn't know about differences between XP & XT crankcases. What I was thinking was that if the deck height was higher in the XT case that might allow the use of the 272 piston without the need for a stack of base gaskets. Oh well, perhaps a spacer out of copper shim stock. The 272XP piston is just too tall to use in the Hyway BB kits for a 372 without a bunch of base gaskets.
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Offline weimedog

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I just put a mako 272 and Jinhua piston together with the wrist pin. was approx. .052 difference in crown height. If the cylinder is like the last one..... big if....  with no base gasket it was .032 squish. So one base gasket would get me to that .052!  A .040 gasket/shim is needed to get that 272 piston to .020 squish.. So there is hope. On the other end there is approx. .115 in difference in skirt height. that translates between 5 and 6 degrees difference on intake timing. Take a gasket moving the cylinder up .040 or loosing a couple of degrees and we are in the ball park. 76- 2 (gaskets)= 74 degrees...then with the .115 in shorter skirt, approx. 6 degrees... that a net 80 degrees btdc. So net net net the other cylinder & piston & .020 stock gasket had .052 squish & approx. 75 degrees btdc....  With the 272 Mako piston & .040 gasket/shim? looks like it might end up close to 80 degrees btdc intake timing and .020 squish.  Of course the other differences would be the windowed piston & change in exhaust & transfer timing, but no change to its large 27 degree blow down ... maybe cutting some material at the base of the transfers,( the cylinder wall away). Might make a mess but also might be an interesting build.

Also did the same thing with a Stihl (Meteor am) 064 piston with interesting results! Only .010 more distance to the crown but the piston skirt was actually longer than the Jinhua piston.....buy .010 Real interesting.. Maybe those Jinhua Farmertec folks know what they are doing? Going by the "old Jinhua (Huztl saw) cylinder, that .010 would in fact get me to .020 squish and it would be easy to grind the intake port lower to get the intake closer to where we want... I think an easier path to an interesting AM build. And the Stihl (Meteor) is also a windowed piston. Also have a X-torq carb, those things along with a muffler with a 3/4 inch pipe should run well. And Loud!

Am I way off???

But back to the 350 build. (modified transfers (hogged out dividers on the vertical section & matched the lower to look like a 346xp both on bearing cap& cylinder), muffler mod, intake lowered, 357xp carb & intake tract. )


Offline KilliansRedLeo

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Well, the reasoning on using the 064 piston in a 52mm  BB kit was nearly the same I had for using the 064 piston on the first one I did. I could have lowered the intake but I was after, 'no grinding required'. That is also why the 272 piston is still on my mind. The 'IF' you mention is a really big one, I've seen as much as 0.015 difference in squish between two cylinders from the same vendor, on the same saw! I do mean 'the same saw' put one jug on, measure squish, then put a different one on and measure again!

Post pictures and results on the 350 when it i done. Your 372 chain brake parts go out in tomorrow AM mail.

Cheers!
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

 

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