07-13-2016, 12:01 PM | #1 |
Not Yet Wild
Join Date: Nov 2012
Location: Fort Qu'appelle Saskatchewan
Posts: 15
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'90 Par Car engine rebuild.
I'm doing a total rebuild on a 90 par car. First engine I've done from scratch. I just installed the new cylinder, head and piston as per instructions. Hand cranking it over it has excellent compression on the upstroke. On the down stroke it pulls a serious vacuum until the exhaust port and intake port open. Is that normal? I don't know if the starter could pull it through the down stroke. Please help me out with any suggestions you may have. Thanks.
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07-14-2016, 07:16 AM | #2 |
Gone Wild
Join Date: May 2011
Location: Pittsburgh
Posts: 2,941
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Re: '90 Par Car engine rebuild.
Yep. Normal. Vacuum is a very good thing with these engines as it is critical for proper fuel delivery. Better still is that if you have good vacuum that means your crank seals are probably good.
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07-14-2016, 06:47 PM | #3 |
Gone Wild
Join Date: Jun 2015
Location: East TN
Posts: 525
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Re: '90 Par Car engine rebuild.
Piston pulls crankcase vacuum on the upstroke and puts crankcase pressure on the downstroke. That is the very basics of a 2 strokes operation.
Oh wait. It sounds like your measuring vacuum on the downstroke through the spark plug hole. During normal operation when the piston gets to the top, the spark plug burns the air/fuel mixture and the piston goes down with pressure not vacuum. You don't have the explosion creating pressure so your measuring vacuum when you go on the downstroke. How are you measuring the this? |
07-15-2016, 10:29 AM | #4 |
Not Yet Wild
Join Date: Nov 2012
Location: Fort Qu'appelle Saskatchewan
Posts: 15
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Re: '90 Par Car engine rebuild.
I was just measuring the vacuum with my thumb over the spark plug hole. Figured out the rest of the 2 cycle operation in the middle of the night. Had a brain cramp. Been working with 2 cycles cince I was ir the boat business in the '60s. Thanks guys your help. I'll let you know how it turns out.
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