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8N Vs 9N/2N compression ratio

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Mike (NM) '49 8

11-04-1999 12:16:37




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OK, here is a stupid question for you! I have seen the specifications for the 8N tractor say the compression ratio is 6.5:1. For the 9N/2N it is spec'd at 6.0:1. If the N's all had the same engine (same pistons, crank, sleeves, etc.) how did the compression ratio change? Maybe I am overlooking some vital element in the 8N engine that is not compatible with the other N's!




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joe m

11-06-1999 11:01:51




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 Re: 8N Vs 9N/2N compression ratio in reply to Mike (NM) '49 8N, 11-04-1999 12:16:37  
same bore same stroke same compression ratio...
May things can be done to increase compression but the ratio remains the same if the bore and stroke are not changed. Rings, vlaves, cam, intake restrictions, piston to head clearance(chamber volume) will and do
determine total cyl compression..



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JHEnt

11-05-1999 17:21:12




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 Re: 8N Vs 9N/2N compression ratio in reply to Mike (NM) '49 8N, 11-04-1999 12:16:37  
I believe the pistons changed in the 8N. One thing I have encountered was a cylinder head that was resurfaced, the machine shop took to much off the head causing the pistons to hit the head on the top of the stroke. Anyone getting a head resurfaced should watch for this.

Ther were also 2 different sleeve thicknesses but I think there was a difference in the block bore in the early tractors.



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Claus

11-05-1999 03:31:40




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 Re: 8N Vs 9N/2N compression ratio in reply to Mike (NM) '49 8N, 11-04-1999 12:16:37  
There is only one way to increase compression ratio on an engine that has the same bore and stroke, and that is to reduce the size of the volume of the combustion chamber. This can be done by doming pistons, decreasing the thickness of the head gasket, but most probably by changing the head design. Care must be taken to allow for valve clearance. Some of the older high compression engines (Before the smog days) had cutouts in the pistons for the valve clearance or a squish band design...(Although the squish band head was primarily for better spark combustion) This would allow for a smaller combustion chamber....
Happy Motoring
Claus

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Charlie in TX

11-04-1999 17:06:53




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 Re: 8N Vs 9N/2N compression ratio in reply to Mike (NM) '49 8N, 11-04-1999 12:16:37  
I have read somewher that the pistons are the difference. The later pistons would fit in the older motors, therefor only the newer pistons are sold. That means a rebuilt older motor now has a 6.5:1 CR.



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bg

11-04-1999 20:56:16




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 Re: Re: 8N Vs 9N/2N compression ratio in reply to Charlie in TX, 11-04-1999 17:06:53  
The old pistons were iron or steel. The new ones are some sort of aluminum alloy. Can't remember if the piston top is different or not.



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David(MN)

11-04-1999 13:10:46




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 Re: 8N Vs 9N/2N compression ratio in reply to Mike (NM) '49 8N, 11-04-1999 12:16:37  
I seem to remember hearing about the 8n's having "shaved Heads", that would explain increased compression ratio. Also if a different gasket material used that is thinner on the 8n that would also increase C.R. Both of these would allow for increased C.R. but the same reciprocating assembly. Either way your 9n has probably been "rebuilt to 8N specs" Good luck David



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Sam (Mo.)

11-04-1999 12:39:54




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 Re: 8N Vs 9N/2N compression ratio in reply to Mike (NM) '49 8N, 11-04-1999 12:16:37  
Mike - other and better mechanics here will no doubt give you a more complete answer, but I vaguely remember reading that switching to iron cylinder sleeves increased the compression some.

Maybe that's part of the answer, at least for the late-model 8N's.



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