How much cylinder taper is TOO MUCH? 92x85 b18C
 

I'm finally getting around to measuring my cylinders and PTW clearance on my build. Specified PTW clearances is .0029" - .0031" (per Wiseco).
I am getting about .0031"-.0033" on all 4 cylinders which I'm fine with, but towards to bottom of each cylinder, the bore gets a little bigger increasing by about .001" and up to .0015" on cylinder 3. This is giving me about .0043" PTW at BDC and .0048" PTW for #3 at BDC.
According to the FSM, the TAPER service limit on a stock B18C is .002". I am aware that a zero taper would be optimal, but unfortunately this would require new pistons and a trip back to the machine shop. So, technically I'm within factory specs, but this is far from a factory spec build (92 stroke x 85 bore).

Do you guys think Ill be OK running this loose at BDC? Im expecting a little piston slap on cold starts, which I'm ok with but im concerned that having .0048" PTW at the bottom of #3 might lead to unacceptable wear on the skirts? Especially since the piston is now coming down a little further than it would with the stock crank.

Again, my PTW is within spec for the top 2/3 of the bore, until I get to about the bottom 1/3 of the cylinder where the cylinder enlarges by about .001" (.0015" on cylinder 3) leading to .0015" taper.

I am considering coating the piston skirts to hopefully closing up my PTW a little bit (about .0005" from my research). Should I be concerned? Or just run it as is? Coat the piston skirts? It looks like I can coat them myself for around $200 which I kinda want to do anyways for the anti-friction properties they claim.

Any input is greatly appreciated!

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

What are you measuring with and what are the details of the block.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

I'm using a Mac bore gauge and some generic Chinese micrometers , both in .0001" graduations. TBH, even though they're some generic mics, they seem pretty consistent and accurate so far. I always check them against the standard before, during, and after measuring.

I mic'd the piston skirts, transferred this measurement to the bore guage, then checked the cylinders. I measured this several times to ensure the numbers were accurate and consistent.
Throughout measuring, I verify "zero" on the bore guage with the micrometer to make sure nothing changes, and also recheck the piston diameter afterwards, so I get a "full circle" of measurements that verify each other.

The bottom end consists of a Darton sleeved B18c, Eagle 5.531" rods, Wiseco/Endyn/Rollerwave 85mm pistons with raised wristpins, Scat standard weight 92mm crankshaft.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Will be an NA build, but might see a small shot of nitrous down the road.
~ 12:1 compression, weekend cruiser street car.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Pix

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Piston diameter is 3.3430". Bore gauge indicates ~.0033" till the bottom of the cylinder where it increases by another .001" and .0015" on cylinder 3.
The piston "rock" seems a bit much when it's at BDC which has me a little concerned...

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

I guess if the 500+ hp turbo guys are ok running at 4 and 5 thousandths ptw, I'll be ok too.... Still might coat the pistons though ...

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Was the block bored with or without a torque plate? I'm thinking it wasn't or else the measurements would be quite different. A good shop should be able to get consistent within a few tenths.

Are you rocking the gauge in the mic to set zero? That is a pain without holding the mic gently in a vise

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

I do not know if the machine shop used a torque plate. They came highly recommended And are pretty well known in my area, but I will NEVER use them again for other reasons.
Yes I very carefully rocked the mic to find true zero. I've tried it both ways with the vice and find it easier to handle the mic and put the gauge in the vice.
I was wondering if I fashioned up some kind of torque plate from an old LS head I have laying around, installed and torqued it down, if it would correctly distort my cylinders and change the dimensions in the right direction.

Thanks for the replies Runnerdown.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

k20a2 oem CAST PISTON bore taper clearance is like 0.002.You need to rebore if you are in the 0.010 range.

with that said since you are forged i dont know if these clearances are okay to run!

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

His numbers are .001-.0015 not .010, that would be off by about a country mile.

With a torque plate a closed deck block will move significantly.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

PTW clearance is at right around .0033" at the top of the cylinders. Towards the bottom they increase an additional .0010" - .0015" giving me about .0043"-.0048" PTW clearance.
Hope that helps clear up any confusion.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

I think im gonna sacrifice an old LS head and attempt to make a deckplate. Ill update this thread when I do this. Either the bores will come back round again, or the machinist screwed up on the hone. Sound about right?

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

So should I be doing all my cylinder measurements WITH a torque plate installed?

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Actually... I think Im gonna take the crank back out, install the head, and measure the bores from the bottom.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

yeah measuring from the bottom may be the easier way without going through all the work of cutting up a spare head...

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Yes
I wish I could find someone to hold tenths...hell, thousandths would be an improvement around here. :cry:

FSM doesn't say to measure with a torque plate, but that's not Darton sleeves either. That would be an interesting study tho..Do it!
I guess you would need a gasket in there to be accurate?
This torque plate debate has always frustrated me.
Some say yes, it's needed.. some say no, locals seem to never have one, especially for a Honda.
I think I'm gonna send my shit across the country next time, and if it comes back screwed...I wouldn't be surprised, just sad.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Is this what you meant to say?
Either way, would you explain more, and what happens with open deck (our stockers?)
And is that MID sleeved block still considered open?
I could understand them moving during boring, but even honing? Is there that much force?

Is not stopping for cool down between cylinders a factor?
I was at the shop watching the guy hone a GSR block, measured straight, when I got it home and it cooled, there was more variance.
It's real hard to get a shop to do 1 and 3, and let it cool, do 2 and 4 the next day..(or even more spacing/cool) for $40-50 for hone they get...ain't happening here, damn them.

How do you Pros do it who can show precision results?

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

From the brief reading Ive done, the head gasket is a good idea. Apparently the fire ring on the HG distorts the bore ever so slightly compared to not using a HG. IDK though, seems so miniscule that it wouldn't matter, but who knows...
Got the crank out tonight. Again. Got my head studs unpacked. I have to clean up some parts before I install them on the block. They've been sitting for a minute and got a little dusty.
Hopefully have some measurements tomorrow if I get around to it and the weather warms up a little. Should be interesting to see how the bore changes.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

It is what I meant to say. The head studs or bolts torqued in place will create distortion in the block. Open decks tend not to transfer that distortion as much to the cylinder. When you close up that large gap with a sleeve liner you now have the forces acting more directly on the cylinder. Ideally, the mains should be torqued as well, some even do the bellhousing bolts too.

I can't comment on every sleeve type but the general idea is to assume nothing. Measuring will show you for sure what is happening. It's all about chasing that precision and learning what it takes to have the roundest cylinders when that engine fires up.

Within the next few days I will reporting back with precise measurements from a K24A2 that is freshly bored with a torque plate. This is a factory sleeve open deck block. Measurements will be taken bare block, then main cap bridge torqued, then with the torque plate and head gasket installed.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

Can't remember if I sent my LS with mains torqued down when it was honed...but it came back out of round and tapered.
Can most machining centers do the setup with 'em on there?
He used a non-cnc Rottler hone.
The bore was improperly done by ANOTHER shop. (too small)

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

need a deckplate my man!!!

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

I assumed they would know this but I don't think they used one. Hoping once I get my head bolted on the taper will improve.
Any thoughts on which way they might change?
Heads on I just gotta find my standard 12pt sockets.

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

lol...stuff disappears in my garage

Re: How much cylinder taper is TOO MUCH? 92x85 b18C
 

I gave up looking so I went to Sears and all they had was a shallow 12pt, so I picked that up but unfortunately it's just a bit too shallow, as the stud starts to push out the extension. Then I got busy on other projects, vacation, birthday parties, etc. I will update when I finish torquing the head and rechecking the cylinders.