Plastigauge help
Discussion
I need to measure my bearings on an LS engine and its been so long since I last did this I cant remember my conversions...
I want my Mains to be in the .0023 to .0025 Range
I want my Rods to be in the .0025 to .0027 Range
Ive ordered some Green Plastigauge that measure 0.007 to 0.020 is this correct to measure that range or am I getting my decimal places wrong #confused
Red does 0.001 - .007
Blue does 0.004 - 0.010
All from ebay.
Many Thanks
I want my Mains to be in the .0023 to .0025 Range
I want my Rods to be in the .0025 to .0027 Range
Ive ordered some Green Plastigauge that measure 0.007 to 0.020 is this correct to measure that range or am I getting my decimal places wrong #confused
Red does 0.001 - .007
Blue does 0.004 - 0.010
All from ebay.
Many Thanks
I've never used plasitgage (just had a brief look at their website now) but your stated target figures lie within the red range, .001 - .007. i.e. .001, .002, * .003... .007. Bond, Jame... 
Edited by BootStrap on Friday 1st February 20:11
Edited by BootStrap on Friday 1st February 20:11
Cant say Ive ever used it myself.
Simple reason, even if something was 1-thou out, there arent any machinists near me who could do anything about it !
And I'm not about to buy a dozen bearing sets just to get the right ones.
I often think half the people posting plastigauge info on the net do so more so they sound good over the internet.
Ive yet to have an issue with bearings on any engine Ive built over the last 20 years and never plastigauged any of them
If the journals measure to spec and are round, I'm happy at that.
Simple reason, even if something was 1-thou out, there arent any machinists near me who could do anything about it !
And I'm not about to buy a dozen bearing sets just to get the right ones.
I often think half the people posting plastigauge info on the net do so more so they sound good over the internet.
Ive yet to have an issue with bearings on any engine Ive built over the last 20 years and never plastigauged any of them
If the journals measure to spec and are round, I'm happy at that.
stevieturbo said:
Cant say Ive ever used it myself.
Simple reason, even if something was 1-thou out, there arent any machinists near me who could do anything about it !
And I'm not about to buy a dozen bearing sets just to get the right ones.
I often think half the people posting plastigauge info on the net do so more so they sound good over the internet.
Ive yet to have an issue with bearings on any engine Ive built over the last 20 years and never plastigauged any of them
If the journals measure to spec and are round, I'm happy at that.
Cheers stevie, well its your old crank and rods im using so hopefully im all good then Simple reason, even if something was 1-thou out, there arent any machinists near me who could do anything about it !
And I'm not about to buy a dozen bearing sets just to get the right ones.
I often think half the people posting plastigauge info on the net do so more so they sound good over the internet.
Ive yet to have an issue with bearings on any engine Ive built over the last 20 years and never plastigauged any of them
If the journals measure to spec and are round, I'm happy at that.
I'm sure they are. But that's my point. If something for whatever reason is 1/2thou or even 1 thou out. What can you realistically do about it, and at what cost ?
And what negative impact will it actually have.
IMO some people are far too anal about stuff like that. If it's a 2000hp race engine then obviously it may matter. Or perhaps an engine sitting at max rpm for hours on end.
But for stuff more normal people use..if the journals are round and within spec. I'm pretty sure the bearings supplied by reputable brands will also be within spec.
There is more chance of the block itself being distorted creating issues than there is the crank or bearings, and that may not show up with plastigauge unless you measure 2-3 places around every single journal and with everything fully torqued up.
And what negative impact will it actually have.
IMO some people are far too anal about stuff like that. If it's a 2000hp race engine then obviously it may matter. Or perhaps an engine sitting at max rpm for hours on end.
But for stuff more normal people use..if the journals are round and within spec. I'm pretty sure the bearings supplied by reputable brands will also be within spec.
There is more chance of the block itself being distorted creating issues than there is the crank or bearings, and that may not show up with plastigauge unless you measure 2-3 places around every single journal and with everything fully torqued up.
A word of caution, this week I have been assembling a 'standard race' MGB engine. I know if the main bearings are too tight as the crank doesnt want to turn freely, caps and shells can be checked if necessary. Too loose? I check using a dial gauge and levering the crank up and down, doesn't tell me how far out but tells me if loose. Big end bearing clearances, will not turn if too tight. To check for loose I press down on the big end cap once the piston/rod has been fitted to the engine, if I feel play I measure it with a dial gauge.....two of my four rods gave an audible clunk on this particular engine. I checked with a dial gauge and the clearances with oil were 2.5 thou, 2.5 thou, 3 and a gnats tesicle thou and 4 thou. On checking more closely the problem was on the big end journal, which will have to be taken down to the next size. Maybe the crankgrinder was a little over zealous with olishing after grinding? Who knows but the book clearance is 1-2.7 thou. With a replacement crank I read 1 thou on all four big ends. I am not a fan of plastigauge as I find it messy and any rotation spoils the measurement. I think one should measure as much as possible and not assume the crank grinder got it right. It can be difficult using basic vernier calipers but once the crank is fitted the dial gauge is well worth trying.
Peter
Peter
PeterBurgess said:
...lots of sound advice...
Peter
IMHO, plastigauge is best used to measure combustion chamber clearances and the method described by PeterBurgess works well for crankshafts. I have used a slight variation of his method when building bottom-ends from scratch to ensure free rotation and correct clearances.Peter
From ancient times -----build crank bearings one at a time at each stage turn crank by hand / torque wrench continue adding rods /pistons 1 at a time you will discover what is tight/wrong in small stages .The guy who taught me this swore that every foot pound above 10 was worth 1 bhp loss on hot A series crank and rods assy and it is very accurate to point out where probs are He would also wipe tight shells out with brasso to get correct feel to a blocck crank assy its time consuming but if each little counts worth it
I tend to measure the bearing gaps with plastigauge (or if I have the time with bore gauge and micrometer). You can adjust the clearnces sligtly if needed. If it is too tight, a leather strap and very fine wet and dry paper, You can polish the journal a bit - taking care to do it evenly. If it is a bit loose, You can put very thin material under the bearing shell.
with bore gauge and micrometer). You can adjust the clearnces sligtly if needed. If it is too tight, a leather strap and very fine wet and dry paper, You can polish the journal a bit - taking care to do it evenly. If it is a bit loose, You can put very thin material under the bearing shell. tristancliffe said:
PeterBurgess said:
Hi Mick
Every 1 lbft is 1 bhp at 5252 rpm.
Peter
Can't tell if serious or if you didn't understand what he was talking about. Every additional lb.ft of bolt tightening torque above 10lb.ft reduces engine power by 1hp. At no point was engine torque mentioned.Every 1 lbft is 1 bhp at 5252 rpm.
Peter
The discussion was about measuring the torque required to turn the crank with perhaps, a tight bearing. This torque required to turn the tight engine is a net loss in engine power.
Steve
Steve is right.
The thread was, if the engine is tighter to turn than it could be this will cost wasted engine power overcoming this 'tightness'. To quantify it so people could see it in a way that is more meaningful (to me anyway, I can almost feel this bhp lost and cry), the relationship between torque and bhp means that at 5252 rpm every 1 lbft 'tightness' equates to 1 bhp, 10 lbs ft means 10 bhp wasted at 5252 rpm.
You don't get 10lbs ft free then lose power, all the resistance to turning costs bhp at the rate of 1 bhp for every 1 lbft at 5252 rpm.
Hope that makes sense.
Peter
The thread was, if the engine is tighter to turn than it could be this will cost wasted engine power overcoming this 'tightness'. To quantify it so people could see it in a way that is more meaningful (to me anyway, I can almost feel this bhp lost and cry), the relationship between torque and bhp means that at 5252 rpm every 1 lbft 'tightness' equates to 1 bhp, 10 lbs ft means 10 bhp wasted at 5252 rpm.
You don't get 10lbs ft free then lose power, all the resistance to turning costs bhp at the rate of 1 bhp for every 1 lbft at 5252 rpm.
Hope that makes sense.
Peter
Edited by PeterBurgess on Friday 15th February 06:56
Steve_D said:
I think perhaps you have missed the point.
The discussion was about measuring the torque required to turn the crank with perhaps, a tight bearing. This torque required to turn the tight engine is a net loss in engine power.
Steve
The discussion was about measuring the torque required to turn the crank with perhaps, a tight bearing. This torque required to turn the tight engine is a net loss in engine power.
Steve
PeterBurgess said:
Steve is right.
The thread was, if the engine is tighter to turn than it could be this will cost wasted engine power overcoming this 'tightness'. To quantify it so people could see it in a way that is more meaningful (to me anyway, I can almost feel this bhp lost and cry), the relationship between torque and bhp means that at 5252 rpm every 1 lbft 'tightness' equates to 1 bhp, 10 lbs ft means 10 bhp wasted at 5252 rpm.
You don't get 10lbs ft free then lose power, all the resistance to turning costs bhp at the rate of 1 bhp for every 1 lbft at 5252 rpm.
Hope that makes sense.
Peter
The thread was. One eyed mick said that overtightening (every unit of torque applied to the bolts) main or rod bearings reduces measurable power output. There is no 5252 relationship between bolt tightness on a bearing cap and engine power output. The thread was, if the engine is tighter to turn than it could be this will cost wasted engine power overcoming this 'tightness'. To quantify it so people could see it in a way that is more meaningful (to me anyway, I can almost feel this bhp lost and cry), the relationship between torque and bhp means that at 5252 rpm every 1 lbft 'tightness' equates to 1 bhp, 10 lbs ft means 10 bhp wasted at 5252 rpm.
You don't get 10lbs ft free then lose power, all the resistance to turning costs bhp at the rate of 1 bhp for every 1 lbft at 5252 rpm.
Hope that makes sense.
Peter
Edited by PeterBurgess on Friday 15th February 06:56
At least I now know you were not being funny, and were merely being serious and mistaken.
tristancliffe said:
Steve_D said:
I think perhaps you have missed the point.
The discussion was about measuring the torque required to turn the crank with perhaps, a tight bearing. This torque required to turn the tight engine is a net loss in engine power.
Steve
The discussion was about measuring the torque required to turn the crank with perhaps, a tight bearing. This torque required to turn the tight engine is a net loss in engine power.
Steve
PeterBurgess said:
Steve is right.
The thread was, if the engine is tighter to turn than it could be this will cost wasted engine power overcoming this 'tightness'. To quantify it so people could see it in a way that is more meaningful (to me anyway, I can almost feel this bhp lost and cry), the relationship between torque and bhp means that at 5252 rpm every 1 lbft 'tightness' equates to 1 bhp, 10 lbs ft means 10 bhp wasted at 5252 rpm.
You don't get 10lbs ft free then lose power, all the resistance to turning costs bhp at the rate of 1 bhp for every 1 lbft at 5252 rpm.
Hope that makes sense.
Peter
The thread was. One eyed mick said that overtightening (every unit of torque applied to the bolts) main or rod bearings reduces measurable power output. There is no 5252 relationship between bolt tightness on a bearing cap and engine power output. The thread was, if the engine is tighter to turn than it could be this will cost wasted engine power overcoming this 'tightness'. To quantify it so people could see it in a way that is more meaningful (to me anyway, I can almost feel this bhp lost and cry), the relationship between torque and bhp means that at 5252 rpm every 1 lbft 'tightness' equates to 1 bhp, 10 lbs ft means 10 bhp wasted at 5252 rpm.
You don't get 10lbs ft free then lose power, all the resistance to turning costs bhp at the rate of 1 bhp for every 1 lbft at 5252 rpm.
Hope that makes sense.
Peter
Edited by PeterBurgess on Friday 15th February 06:56
At least I now know you were not being funny, and were merely being serious and mistaken.
One eyed Mike was referring to applying a torque to the end of the crankshaft to measure how stiff the latest assembled main bearing is. He is not referring to torquing the main bearing cap bolts.
Steve
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