86 Par car cylinder bore

mmattingly · 07-30-2017, 05:06 PM

I have an 86 Par car that has been running great. Suddenly lost compression down to 60 lbs. I pulled the jug and found the jug was badly scored from the rings sticking. I'd like to see about boring the cylinder and using a larger piston. It is currently standard bore. Any suggestions will be appreciated.

Lochlin · 07-31-2017, 09:57 AM

It's 2.75 in (69.8mm) as standard.

Personally, I would just get a whole new top end kit to make sure everything jives. They aren't a ton of cash. That's just me, though. Over bore should get you a bit more ooomph.

mmattingly · 08-14-2017, 10:26 PM

That's what I did. New cylinder, piston, rings and still only 60 lbs. put in new crank seals and still only 60 lbs. Tried a different compression gauge and still 60 lbs. I am stumped.

Lochlin · 08-15-2017, 08:33 AM

Well, you have me stumped as well.

Let's think this through. Compression is pretty much contained to the top end so the crank seals shouldn't impact much.

You are certainly losing compression somewhere and, with the new cylinder and assuming you put the piston and rings on right, then there really isn't a whole lot of places where you can be losing air.

Amateur question but I have to ask, you put the piston in right, correct (EX on top of the piston towards the exhaust port on the cylinder)? Assuming you did this right then there are only two places where you can possibly be losing compression out the top and that's the spark plug hole (which is pretty much impossible with the new cylinder) or one of the gaskets (head or base gasket). I think you can double up on the gaskets if you need to but don't quote me on that. Maybe try some sealer in addition to the gaskets? Dang it. That's frustrating. I feel for you for sure.

I am going to PM another member to take a look a this at thread as well.

Spicyunicorn · 08-15-2017, 12:26 PM

I'm not a big fan of the rebuild kits they come from China and there isn't the best quality control over there I prefer to have my local machine shop bore them out that being said pretty odd you have exact same number after rebuild did you twist the jug when the piston was inside? That can break rings did you gap the rings? How did the head look? It's possible you may be loosing compression there

07-30-2017, 05:06 PM	#1
mmattingly Not Yet Wild Join Date: Mar 2013 Posts: 27	86 Par car cylinder bore I have an 86 Par car that has been running great. Suddenly lost compression down to 60 lbs. I pulled the jug and found the jug was badly scored from the rings sticking. I'd like to see about boring the cylinder and using a larger piston. It is currently standard bore. Any suggestions will be appreciated.
mmattingly Not Yet Wild Join Date: Mar 2013 Posts: 27

07-31-2017, 09:57 AM	#2
Lochlin Gone Wild Join Date: May 2011 Location: Pittsburgh Posts: 2,948	Re: 86 Par car cylinder bore It's 2.75 in (69.8mm) as standard. Personally, I would just get a whole new top end kit to make sure everything jives. They aren't a ton of cash. That's just me, though. Over bore should get you a bit more ooomph.

08-14-2017, 10:26 PM	#3
mmattingly Not Yet Wild Join Date: Mar 2013 Posts: 27	Re: 86 Par car cylinder bore That's what I did. New cylinder, piston, rings and still only 60 lbs. put in new crank seals and still only 60 lbs. Tried a different compression gauge and still 60 lbs. I am stumped.
mmattingly Not Yet Wild Join Date: Mar 2013 Posts: 27

08-15-2017, 08:33 AM	#4
Lochlin Gone Wild Join Date: May 2011 Location: Pittsburgh Posts: 2,948	Re: 86 Par car cylinder bore Well, you have me stumped as well. Let's think this through. Compression is pretty much contained to the top end so the crank seals shouldn't impact much. You are certainly losing compression somewhere and, with the new cylinder and assuming you put the piston and rings on right, then there really isn't a whole lot of places where you can be losing air. Amateur question but I have to ask, you put the piston in right, correct (EX on top of the piston towards the exhaust port on the cylinder)? Assuming you did this right then there are only two places where you can possibly be losing compression out the top and that's the spark plug hole (which is pretty much impossible with the new cylinder) or one of the gaskets (head or base gasket). I think you can double up on the gaskets if you need to but don't quote me on that. Maybe try some sealer in addition to the gaskets? Dang it. That's frustrating. I feel for you for sure. I am going to PM another member to take a look a this at thread as well.

08-15-2017, 12:26 PM	#5
Spicyunicorn Gone Wild Join Date: Jun 2015 Location: NW Iowa Posts: 1,669	Re: 86 Par car cylinder bore I'm not a big fan of the rebuild kits they come from China and there isn't the best quality control over there I prefer to have my local machine shop bore them out that being said pretty odd you have exact same number after rebuild did you twist the jug when the piston was inside? That can break rings did you gap the rings? How did the head look? It's possible you may be loosing compression there

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