ENGINE SIZE.... How close is too close?

[dw230]

If the engine is being built that close to the limit you must be prepared to pull a head. An engine that close will have to be measured at ambient temp because it will be too big when measured hot.

We use dial verniers to measure and while the quality of some tools is better than others, the person using the tools can be a factor. If the engine is difficult to reach that can also add a few thou to the measurment. A tilted caliper does not read the same as one that is dead-on perpendicular to the bore.
Pistons down in or out of the bore factor into the stroke measurment too.

An engine this close will not be measured with air or oil, the methods are not accurate enough. If it is a center plug head we sometimes use a dip stick that drops into the bore and expands to touch the cylinder walls and a stop is set. The tool is collapsed and withdrawn from the cylinder, it is then opened to the stop and measured with calipers. The stroke is set by bridging the bore and using a rod to set on top of the piston. A stop is set, the crank hand turned and the top of the stroke is set with a stop. The measurment between the stops is the stroke. As you can see there is a large amount of room for error here, especially when the wind is blowing hard, the dust is flying or the rain has begun.

This is all done outside in the elements not in a clean room. Need I stress any more that caution should be exercised when building for a displacement class?

DW

[Cajun Kid]

DW,, how close is to close to use "the pump" ?

My "E" motor is  255.6 Cu in,,  The Limit is 260.99....  Should I ever have the Honor of being in impound and having to be checked,, what could I expect ?

Thanks

Charles

[Seldom Seen Slim]

Measurement method is at the discretion of the officials doing the measuring, I believe.  If the number you tell him is close to the upper limit he'll most likely opt for careful measurement using gauges and such.  If your claimed displacement is way off from the limits of your class -- he'll PROBABLY try to pump it first.  if there's any question about the results he may next ask you to let him measure it with the dial gauge.  And DO NOT EVER lie about the displacement and hope he'll just use a pump - only to find you were way off and now he's going to measure each and every cylinder and do it very carefully and not cut you any slack (beer in your hand or not).


How close is too close for a pump?  Maybe 10%, maybe more -- but since the pump method isn't very precise -- if you're close -- have a spare head gasket in hand and just smile when you're asked to pull the head.

[willieworld]

engine has to be not within 3 % of the upper cc limit to be pumped---page 11 top of page scta 09 black book---  now the motorcycles are allowed their upper limit + .020 overbore --.050 in vintage ---none for production page 105 09 rule book----------------------willie buchta

[doug odom]

First, when I bore and hone a motor I can measure a 1/4 thousands difference with my inside mic by feel. With my dial bore gauge it is about a 1/2 thousandth because of no real feel. If I could not get within 1/2 thousands I would throw the thing in the trash.

I have been lucky enough to have had 3 of my motors pumped in impound and every time the pump was right on.  DW is pretty good with that pump machine. 

[McRat]

Problem with dial bore gauges is the tips eventually flatten and you can't trust them after that.  Yeah, there are replaceable, IF you have replacement tips.  And you need a decent gauge block set (or a dedicated ring) to set it.  And you need to use it alot.  But when set up right, you should get ±0.0001" readings in hard metals, and about twice that in soft metals.  The tips actually wears about a .0001" groove in soft metals, so don't rock it more than you need to.  If you need tighter than that, time for air gauging.

[Seldom Seen Slim]

I've heard lots of people say lots of things about Dan Warner -- but this is a first:  "DW is pretty with that pump machine." 

I mean no disrespect, Dan -- but I've never considered you to be pretty.  Maybe Doug meant to say that you're "pretty good" with the pump.

[McRat]

Grooovy Baby!

The Swedish import version, right?

[SPARKY]

If it is that close,    I would sure plan on being able to run ICE water through the block before I got to tear down 

[panic]

And TDC is defined as which:
1. highest point of piston travel
2. 0° of crankshaft rotation?

I'm sure some of you see where this leads...

[gearheadeh]

If the engine is being built that close to the limit you must be prepared to pull a head. An engine that close will have to be measured at ambient temp because it will be too big when measured hot.

We use dial verniers to measure and while the quality of some tools is better than others, the person using the tools can be a factor. If the engine is difficult to reach that can also add a few thou to the measurement. A tilted caliper does not read the same as one that is dead-on perpendicular to the bore.
Pistons down in or out of the bore factor into the stroke measurement too.

An engine this close will not be measured with air or oil, the methods are not accurate enough. If it is a center plug head we sometimes use a dip stick that drops into the bore and expands to touch the cylinder walls and a stop is set. The tool is collapsed and withdrawn from the cylinder, it is then opened to the stop and measured with calipers. The stroke is set by bridging the bore and using a rod to set on top of the piston. A stop is set, the crank hand turned and the top of the stroke is set with a stop. The measurement between the stops is the stroke. As you can see there is a large amount of room for error here, especially when the wind is blowing hard, the dust is flying or the rain has begun.

This is all done outside in the elements not in a clean room. Need I stress any more that caution should be exercised when building for a displacement class?

DW

Thank you Dan W. for your reply, I highlighted in red the points I found to ring true. I had to reread the part in purple about the piston stop bridging the bore on top of the deck. Is this device magnetic or bolted onto the block?
I understand about how the elements are going to play in this, 1 it is going to get into your engine(sand,salt etc.) 2 the conditions play a part in the inspectors willingness to hang from his ankles to get access into a tight engine compartment.In order to make sure the vernier is square to the deck and bore! I got from Stainless about how it is good to expect a teardown and have a good attitude, Easier for me as I have been a tech inspector for other types of racing in the past. Sparky thanks for the hint that it would be so close that I should consider airconditioning the block on the return with ice water to shrink the block, I could even hose it down with CO2 but I would think that these kind of activities would arouse quite abit of attention! Panic brings up the idea of ....where is TDC. What I think he is saying is that it is important for the dial bore gauge or piston stop to be placed on top of the piston in just the right place. If a D.B.G. is used and it doesn't travel exactly parallel with the piston in it's travel the measurement is off. With the stop or the D.B.G. it is also possible to have it located too much on either side of the wrist pin axis causing an overly loose piston to rock in the bore. If the piston rocks unnoticed this could effect the measurement of stroke. So the moral of the story is don't build a loose engine (piston wise) with a wrist pin that is offset alot. As this will show up in more piston rock at T.D.C. Thanks Mcrat for the tip about the tips of dial bore gauges needing to be fresh. Doug Odom will now have to live down his typo for calling D.W.   PRETTY........good with the pump! The one post that really opened up my eyes  was what Nortonist wrote: basically about in 3 different measurements he got a result that varied 2.5cc  from 497,498 to 499.5 on I assume a 500cc single? cylinder engine! So with Willie's prudent suggestion to stay away from the top by at least 3% Iam going to take all of the excellent advice from all of you and use smaller pistons!

Thanks again,

[willieworld]

ive had my motor measured 6 times the largest was 985.86 the smallest was 983.26 thats not bad  considering carbon buildup and cold and heat ---my bore and stroke are 3.50 X 3.125 =985.383084 cc--if my bore was mismeasured by .004   3.504 X 3.125 = 987.637459 cc total differance is 2.254 cc---the top of my class is 1000 cc but in the motorcycle classes (except production) we are allowed 1000cc plus a .020 overbore (.050 in vintage) if i had a v8 it could be 4 times as bad as me 2.254 X 4 =9.016 cc which is .55019 cu in  ---i asked to have my engine pumped and was told that i shouldnt if my motor was within 3% of the limit and if i had it pumped and it failed then that was it i would have to reset the record and then tear the engine down---    just some thoughts       willie buchta

[doug odom]

One thing that was missed in this thread was if you are talking about an Iron or Aluminum block. Aluminum blocks walk all over the place as the temp goes up so I can see where the different measurements might come from.  And to DW Sorry about the typo. I guess I should have said cute not pretty. That is what I get for not reading my own writing.

[McRat]

I would hope they'd have some kind of allowance for measurement error, 1/2% maybe?  That's 5cc's on a liter.  Piston flatness, piston rock, deck flatness, positive deck height, bore roundness, variation of bores, and measure tool resolution & accuracy can all come into play.  I think it falls under common sense though.

[jimmy six]

Even tho I haven't in the last 2 years, I have pumped countless engines when working with Dan in impounds. When used correctly it will give cylinder cubic inches very, very close to what a measured cylinder would give. Cylinder temperature has a BIG factor in doing this. There is an included calculation sheet with every pumps; some are in 1/2 degree increments. Larger engines are the hardest and need special adapters for the spark plug holes (the SCTA has all these Steve Shotrosky and I made them) M/C's may have different needs.

2 examples come to mind, one was Oldsmobile engine which the competitor was sure it was over 440" and in the "A" catagory. I pumped 3 different cylinders and could not come up with a number over 436". Not wanting to give up the competitor took off a head and we measued the engine at 436. It had a 425" crank in it and not a 455".  The second was a streamliner with a 1000cc Honda that I pumped with a 3/8" speed wrench at 996cc. Later in the week the head was off and I measured it at 996.

When learning how to use it I pumped my own engines many times in the off season both cold and hot and always found the pump with in 1 inch of what it is.

If you have a close engine, I guarrentee I can pump it too big; but I would not be doing it correctly. Every 2 years I sent the pumps to a place in Texas to have them checked and calibrated. They were the ones who instructed me on how to do it correctly and that's what I shared with all who wanted to learn. At the time NASCAR used pumps sporatically thru the garage area and used the same method. I'm sure winners were treated differently. . . JD