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Cutting down cylinders in a lathe
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risk
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PostPosted: Fri Apr 05, 2013 12:19 pm    Post subject: Cutting down cylinders in a lathe Reply with quote

Can someone give me some tips on cutting down cylinders in a lathe?

Where do you indicate off of and how do you get all four cyls the same length?

Right now I have about 0.085" deck. I need to take about 0.035" off each one to get my deck height a little tighter.

From what I have read, most take the length off the case end? A step by step would be awesome.
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75smith
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PostPosted: Fri Apr 05, 2013 1:19 pm    Post subject: Reply with quote

to cut down a cylinder-case end

first measure from top of cylinder to the next step, this could be the fin, or other step-this is needed later and can vary from cylinder to cylinder

next chuck up the top into a 3 or 4 jaw chuck-make sure that the step you measured to is at the edge of the chuck-also make sure it is square

now you figure out the distance from the edge of the chuck to the end of the barrel(to the point it enters the case-as you are removing X amount from that ledge)

use that distance and the distance you measured in step 1, add, should be XX.XX, now you can take a cut X at the ledge-done

there are more precise ways-like using an inside chuck(grabs cylinder from inside-then all you need to measure is from barrel top to barrel bottom, but you should get the general idea(or your machinist should)
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mark tucker
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PostPosted: Fri Apr 05, 2013 1:27 pm    Post subject: Reply with quote

I made fixtures to center the cylinder on both ends, chucking a cylinder in a chuck isant the best thing to do. then cut them to length. or you can use a set of .100 longer rods and a shim to get what you want. either way will do.
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raygreenwood
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PostPosted: Fri Apr 05, 2013 1:34 pm    Post subject: Reply with quote

Or.....you can take the case to a good machinist with a mill and while having both sides of the case decked (the cylinder spigot holes)...which you should do with any serious build just to set the decks parallel and equal to the crank centerline.....you can take out enough to bring your deck up tighter. Ray
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risk
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PostPosted: Fri Apr 05, 2013 1:37 pm    Post subject: Reply with quote

I guess I should have provided more info.. the case has been decked already.

It's a turbo motor and I have the top end off due to cracking two cylinders. I don't want to tear it down, or buy new rods.. so my only option is to cut the cylinders.
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mark tucker
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PostPosted: Fri Apr 05, 2013 1:55 pm    Post subject: Reply with quote

you can even use some 1" thick wood to make jigs to hold the cylinder. 3/4 bolt in 1 and a chamfered hole in the other, set them up in the laythe and cut them so the cylinder fits nicely and use the live center to hold it togeather.dial indacate the cylinder & cut it to spec.I use my dro but a good set of calipers will also do. you can mark the wood in a position for checking index. and mesure to the portion your cutting. then subtract the amount you need to cut. you need to do this on each cylinder as they may seat a bit deeper or shalower. just simple back yard stuff I learned while doing some mill spec stuff.
if your spigot hole is a little big you can also tighten up the fit a bit.or make a 90.5~92 cylinder fit a 94 hole. theres a lot of ways to skin cats,just dont get scratched or arested.
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nsracing
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PostPosted: Fri Apr 05, 2013 2:08 pm    Post subject: Reply with quote

Is this your first time to use a lathe??

To answer you question, the best way is a dedicated mandrel for the cylinder when you take off the material. And material can be taken off either on sealing side or skirt side.

If you don't have a mandrel, then obviously use the chuck...3 jaw or 4 jaw. And whatever you do, DO NOT just chuck the cylinder and take the cut or it WILL fly off the chuck and kill you!! You need an end-support on the tail to keep it steady. A large 1/2 inch aluminum plate and countersunk in the middle to put your tail center will do fine. Just push it on backside and hold there against the chuck. This is as secure as it will get. Always be safe. Then make as many cuts as you need.

To make them all even, just use a bed-stop to chuck all the other cylinders after you figure out the final dimension from the first cylinder. Just matter of repetition of the first process -like production work.
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PostPosted: Fri Apr 05, 2013 2:58 pm    Post subject: Reply with quote

Do what I did- use a brake lathe. Self-centering, and it's the same material as a brake disc or drum. Find the correct centering hubs for the size cylinder you're using, mount it with the jug/case end facing the drive motor. Cut whatever you need, measure your progress with a caliper. It'll get close enough to work, my engine has been together for 4+ years with jugs done this way.
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modok
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PostPosted: Fri Apr 05, 2013 4:44 pm    Post subject: Reply with quote

There are lots of ways, and of course it depends on how good your lathe is and what you DO have and ect. A four jaw holds a cylinder sleeve a lot better than three jaw. I do use brake lathe centering rings at the tailstock when doing this( trimming dry sleeves), but they are sometimes not very accurate, so there is much shimming and dialing in. And what if you don't have the right size?

if you want to really take the time and so forth, try this:
Make a centering bushing that is a light slip fit in the bore. This way you can clamp either side without distorting the cylinder, and if make it with a ledge(you know, small flange) on the end, and a true hole in the middle then that can be used against a live center at the tailstock, and center very well! I imagine you will end up cutting case side, and having the head side in the jaws, but it could be done other ways also depending on how it fits. If you have or make an expandable mandrel that goes inside then you could cut either side, but they are expensive and rather complex to create. Worse case if all you have is a little three jaw OR nowhere to indicate the head end then maybe you have to make two bushings. Then you can indicate in the bushing true and THEN put the cylinder on, and it will be perfect:D Or maybe you can chuck at the ID of the cylinder, but yikes, quite risky if it should slip.

Where to get the material? slice the tops off some old 4" bore pistons Wink and, of course, how to make them? well you DO have a lathe...right?

Don't underestimate how flexy the bottom part of the cylinder is. I did a motorcycle one today, on these I use a hose clamp on the bottom because otherwise it flexes out of the way of the hone and ends up small. So I put the hose clamp on it and tightened, it became .003 small Shocked so I loosened the clamp a little, only want about .001 small. And that's just a hose clamp on a 67mm bore, these are even bigger and thinner!


Last edited by modok on Fri Apr 05, 2013 5:08 pm; edited 1 time in total
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PostPosted: Fri Apr 05, 2013 5:08 pm    Post subject: Reply with quote

nsracing wrote:
Is this your first time to use a lathe??

To answer you question, the best way is a dedicated mandrel for the cylinder when you take off the material. And material can be taken off either on sealing side or skirt side.

If you don't have a mandrel, then obviously use the chuck...3 jaw or 4 jaw. And whatever you do, DO NOT just chuck the cylinder and take the cut or it WILL fly off the chuck and kill you!! You need an end-support on the tail to keep it steady. A large 1/2 inch aluminum plate and countersunk in the middle to put your tail center will do fine. Just push it on backside and hold there against the chuck. This is as secure as it will get. Always be safe. Then make as many cuts as you need.

To make them all even, just use a bed-stop to chuck all the other cylinders after you figure out the final dimension from the first cylinder. Just matter of repetition of the first process -like production work.



Did that myself once. Very Happy but only once.
Now i use a mill
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PostPosted: Fri Apr 05, 2013 6:14 pm    Post subject: Reply with quote

Some sound advice here. Like mentioned already make yourself a mandrel to properly support the barrel. I also suggest practicing on a barrel you don't care about messing up first before you chuck up the ones you are gonna use on your engine build.
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risk
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PostPosted: Fri Apr 05, 2013 8:31 pm    Post subject: Reply with quote

Jimmy111 wrote:
Did that myself once. Very Happy but only once.
Now i use a mill


How do you cut them in a mill? rotary table?
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morymob
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PostPosted: Sat Apr 06, 2013 4:13 am    Post subject: Reply with quote

Been awhile but i had a 36 eng that i experimented on , get comp high as posible and more carb. Kept cutting down cyls and removing metal inside head until about 70tho clearance between piston and valves. Had to use later starter to crank and at the time had good gas and took highest octane. Put into an'65 bug and tweked some, sure pepped it up , couldn't do that at all with todays gas. Cut cyls on 4 jaw self centering lathe, was a fun experiment.
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andy198712
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PostPosted: Sat Apr 06, 2013 4:58 am    Post subject: Reply with quote

Why not fly cut the heads?
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Quokka42
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PostPosted: Sat Apr 06, 2013 5:36 am    Post subject: Reply with quote

Obviously he wants to reduce that deck. If the pistons are .085 down the hole, flycutting is not going to get him any squish back.
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PostPosted: Sat Apr 06, 2013 6:17 am    Post subject: Reply with quote

Quokka42 wrote:
Obviously he wants to reduce that deck. If the pistons are .085 down the hole, flycutting is not going to get him any squish back.


He can always add another turbo to fill the extra .085 space...yah!, just run 2 turbos and that motor will think its a big block Chevy...like they say the more air fuel you can compress equals more power right?

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PostPosted: Sat Apr 06, 2013 9:01 am    Post subject: Reply with quote

risk wrote:
Jimmy111 wrote:
Did that myself once. Very Happy but only once.
Now i use a mill


How do you cut them in a mill? rotary table?

You can do that but I have a cnc mill.
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PostPosted: Sat Apr 06, 2013 10:22 am    Post subject: DH Reply with quote

Why not just sell your rods and go with 0.100" longer? I had the same issue and sold my 5.4 H-beam rods and replaced with CB 5.5's and then simply shimmed accordingly to get 0.050" DH.
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PostPosted: Wed Jun 26, 2013 10:37 pm    Post subject: Cylinder splits, Reply with quote

How much boost are you running? WOW! Did you get any oyher damage?(Pistons?) Now that Pauter Machine doesn't make the Power Sleeves anymore, I thought for sure someone was making a 92mm to 94mm Sleeve for the heads (to make up the 94mm to 92mm Cyl. size diff)?? I was looking for a set for a Great pair of 94mm heads to go down to a set of Biral 92mm cyl's? May have seen them on a very old Rimco price list? Or after ckecking the cc's in heads, maybe recut Head bore enough for 92mm cyl to stay? (They are a Mathamatical Guess near 36cc-37cc now!?) G-Man
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risk
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PostPosted: Thu Jun 27, 2013 5:42 am    Post subject: Re: Cylinder splits, Reply with quote

vdubwizard wrote:
How much boost are you running? WOW! Did you get any oyher damage?(Pistons?)


25-30 psi.. here's the thread.

http://www.thesamba.com/vw/forum/viewtopic.php?t=5...mp;start=0

I bought a lot of old midget race parts and some of the 92mm cylinders were sleeved up to 94mm like you describe. Sold them on here a while back. Seems like any good machine shop could make you some.
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