It's time to do a BIG bore

[mrriggs]

I hope I didn't start this thread prematurely but I just got the OK from my better half to spend a good chunk of our tax return on my big bore project. I've been planning it for a long time and have slowly collected the necessary tooling. Now I can get the last few things I need.

I will be using 87mm flat top pistons from an Isuzu and making my own nodular iron sleeves. The goal isn't to make a screaming race motor. I'm actually shooting to make the same power as a stock engine, but at a much lower rpm.

The first step will be making a fixture and torque plate. Stay tuned...

[tonyc2me]

Sounds like something I would like. Stock cam? Re-phased crank? Tony C

[mrriggs]

Feb 7, 2013 0:06:44 GMT -5 tonyc2me said:

Sounds like something I would like. Stock cam? Re-phased crank? Tony C

I will be using a stock cam, advanced to lower the power band, but plan to eventually design my own cam.

Re-phased? Of course.

[mrriggs]

The goodies are trickling in.

[mrriggs]

Still slow going. Waiting for more parts and I have a couple other projects that I need to finish first.

Last night I removed the stock sleeves from the jugs. I had read about the oven trick (heat in oven until the sleeves fall out) but I didn't want to stink up the house and make a bunch of noise with everyone sleeping. Instead, I propped it up on the bench and warmed it up with a heat gun. It only took about ten minutes per hole. Heat until the oil residue starts smoking then one little tap and the sleeve fell right out.

[Brian]

I did mine in a barbecue by mistake. Was trying to dry some heat paint, heated the cylinders in the barby, and when checking found the cylinder had slipped down and was sitting on the grill grate. Sleeves extending well above the gasket surface of the cylinders. I believe the paint cure was for 250 degree and that was the temp I was trying to get too.
So any body wanting to remove sleeves on your XS, get out the old barby.

PS: de-grease everything first so you don't ruin the flavor of your barby.
HA HA
Wife never knew.

[Brian]

Question;
My re-phase was via a new center pin and donor crank web for a 270 crank. The 277 crank is just a pull apart and re-align the splines, so no donor parts required, nice.
Could the splines be filled in and re-cut on the web to give you the same results as the pin change, but avoid the need for a donor crank and the expensive pin?

[tonyc2me]

Brian if you could do that you could just make a new pin yourself.

[Brian]

What I was meaning was to use the existing crank where the pin is part of one web already and just changing the spline in the opposite web to obtain the desired 270. Either by filling in and re-machining the spline or some kind of adapter spline arrangement.

Sorry mrriggs, didn't mean to mess up your post.

[mrriggs]

I'm still not ready to jump into this project but figured I'd post a few more pics just to keep the thread alive.

I found some sleeves that are real close to the size I was going to make. They are "wet" sleeves from an Allis Chalmers tractor. The wall is over 5mm thick! That should alleviate the distortion issues for which big bores are know. Shown below, next to a stock sleeve.



Obviously, they will need to be shortened, and I'll have to work the flange and the OD at the bottom.

Next is a shot of the stock piston next to the Isuzu piston.



The Isuzu piston is a true flat top with no dome or dish. This can actually work when you go this big because the increased swept volume makes up for the lost dome.



The compression height is basically the same as the stock piston. I'll have to deck it a bit to get everything lined up. That's [one of the reasons] why I haven't started on this project yet, I need to get my surfacing grinder up and running first.

To get an idea of what kind of valve reliefs these flat tops will need, I chucked a junk stock piston in the lathe and faced it at the deck height.



The stock valve reliefs are actually quite generous so it would appear that I won't need any relief for the exhaust valves and shallow ones for the intake valves.

[Burns]

how do you get the cylinder bores big enough to take those sleeves? Are you getting close to (or into) the cam chain tunnel?

[mrriggs]

A lot of metal will be hogged out of the jugs but the sleeves will not protrude into the cam chain tunnel.

The standard convention is to press iron liners into aluminum cylinders. The cylinders provide the support and the liners provide the wear surface. What I will be doing is more like pressing aluminum cooling fins onto iron cylinders. The iron sleeves are thick enough that they won't depend on the aluminum jugs to keep them round.

[jack]

Good luck to you in getting the compression any where 8 to 1 with those flat tops. Even a 85mm bore needs a generous amount of dome -16 to 20ccs due to the deep volume of the C/C. For an open chamber like the XS,.100 or + a few will be needed for 5cc reduction if my memory serves me right. On my welded up chamber for a 10cc reduction would require .100 removal. You can remove .060 from the head but not near the exhaust port,must follow the out line of the H/G. Those flat top pistons compression heights fall way short from standard by looking at your pictures. I personally don't believe you can over come this by piston bore volume alone and theoretically throwing some #s out, you might achieve a 6.2 compression but good luck to you!

The biggest problems you'll encounter with bore volumes of this magnitude will of course be over heating as there simply isn't enough meat left after machining to dissipate the heat,unless you plan on welding or machining a billet block with thicker and deeper heat fins and oil leakage based on my conversations with PJ and with his conversations from others who've tried big bores over 83mms.

[mrriggs]

I've done the math and compression will not be a problem. If I just slapped it together with zero deck height, .030" gasket and stock head it would be about 7.8:1 compression. I can easily take that up to around 8.3:1 by shaving the head or turning a small dome on the piston. The crowns on these pistons are insanely thick so I will likely just turn the pistons and leave the head alone.

[mrriggs]

Check it out. I found an off-the-shelf piston that's a direct drop-in for this motor.



Well... I may need to knock a little bit off of the dome.