1992 evolution cylinder size
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Cruiser
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From: CT
1992 evolution cylinder size
I am having my cylinders bored .020 over. Now the cylinders are said to be 3-1/2" and the pistons are said to be 3.498" Is this right? Should I order 3.498 pistons .020 over or 3-1/2" pistons .020 over? Or is it the same thing? I just don't want to throw my money away. Also, is anything else necessary to change while I'm doing this? The bike is a 1992 heritage 1340 80". It has Andrews ev27cam, machined breather gear instead of that plastic one, Torrington bearing, crane adj. pushrods and crane tappet wheels, polished up intake and exhaust valves and ports, se intake and exhaust, and for the primary side, I put new clutch plates and a new compensator sprocket, as well as all new seals and gaskets, as well as an inner primary o-ring. Let me know what you think and if you could also give me some advice on the piston compression I should go with and if I should get domed or flat topped. The stocks are flat with 8:1 compression I think. And anything else "necessary" I will need. I'm going broke here so I'm going cheap. Thanks, Glenn
Last edited by homiegfunk53; Jul 22, 2013 at 07:28 PM.
Seasoned HDF Member
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From: NW AR
I'm not an expert in this particular area, but MY OPINION is to up the compression a bit, as the stock 8:1 is a bit low by modern standards. You can do this with pistons, I think. Others will have specific recommendations. I think I would go to 9:1 or 9.5:1 eventually when I do my bike (only has 80K on it, so not time yet.) Next, get the pistons first, bring them to the machine shop with your jugs and have them honed to match the pistons at the clearance spec'ed in THE BOOK. And make sure you use a machine shop that does HD work and has the torque plates to properly do Evo jugs.
Stellar HDF Member
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From: Boston, MA
Torque plates are a necessity from the experts since I joined this board. I called around and read a lot last year when I did my top end gaskets.
The good doctor will not lead you astray.
The good doctor will not lead you astray.
Club Member
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From: Bedford UK
Don't over-think the size! All you need is +.020 pistons for your 1992 Evo. However as you ask, have you had an expert inspect your cylinders? To rebore them you will need to have them machined by someone with the correct tools and expertise, who can also check them first, before reboring them, to confirm the best size to bore them to. This could equally as well be +.010, if wear is low, but could exceed +.020 in extreme cases.
Added to that the pistons will come with instructions for bore diameter and ring gap fit, all of which are best left to your expert indy. He can also supply suitable pistons, so don't buy before you visit. As Dr H suggests, ask about a small boost in CR over stock at the same time.
Added to that the pistons will come with instructions for bore diameter and ring gap fit, all of which are best left to your expert indy. He can also supply suitable pistons, so don't buy before you visit. As Dr H suggests, ask about a small boost in CR over stock at the same time.
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Cruiser
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From: CT
Its an auto shop who says they do bikes a lot. He called today and said it only needs .10 over and also said to bring the pistons in first. Will I notice if I go .20 or .30 over with the cam and chit in it? Torque plates I did not ask, but I will. As for compression, I was gonna stay same, but should I bump up to 9? Thanks for advice, Any more? Glenn
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From: Coromandel Peninsula New Zealand
Its an auto shop who says they do bikes a lot. He called today and said it only needs .10 over and also said to bring the pistons in first. Will I notice if I go .20 or .30 over with the cam and chit in it? Torque plates I did not ask, but I will. As for compression, I was gonna stay same, but should I bump up to 9? Thanks for advice, Any more? Glenn
Double check the torque plate thing, if you get a vague answer then go somewhere else, they either have them and know how to use them or they don't. there is no in-between.
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From: Bedford UK
This is what torque plates look like. They support the cylinder while it is being machined. Harley cylinders can easily distort if machined but not using them, so this really is a very important thing to check!
He wants the pistons first, as I mentioned earlier, because they will give him the precise size and tolerance to machine the bores to. A bigger bore such as +.030 will do nothing for performance! If you can buy 9.5:1 or 10:1 pistons, they will work well with your EV27 cam.
He wants the pistons first, as I mentioned earlier, because they will give him the precise size and tolerance to machine the bores to. A bigger bore such as +.030 will do nothing for performance! If you can buy 9.5:1 or 10:1 pistons, they will work well with your EV27 cam.
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From: Coromandel Peninsula New Zealand
It isn't that they can distort when you bore them, they distort when you take the heads off and the torque plates compress them like they were on the bike and they go round again....so you bore them compressed.
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Its an auto shop who says they do bikes a lot. He called today and said it only needs .10 over and also said to bring the pistons in first. Will I notice if I go .20 or .30 over with the cam and chit in it? Torque plates I did not ask, but I will. As for compression, I was gonna stay same, but should I bump up to 9? Thanks for advice, Any more? Glenn
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Cruiser
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From: CT
Spoke with owner today. Torque plates are their. He told me it's up to me as to how much bore so I figured .020 just to make it worth the money and get a little umph out of the bike. I was planning on keeping the flat top pistons so I don't have to monkey around with the heads as I already had the valves port and polished. So if I go .020 over on the pistons, I should def notice a difference with the ev27 and the port polished heads right? As for the pistons compression, bumping up to 9:1 won't involve any other necessary work or add ons right? I Haven't ridden since the bike was stock and am on a back burner type budget. It was my father's just trying to get it back on road. Let me know, I need to get the pistons down to the shop asap. Thanks guys
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