boldy205 74 Posted January 7, 2007 Hi, im in the process of rebuilding my mi16 and have herd about measuring gap in the bottom end bearings with this stuff. What is it exactly and do ihave to use it? Thanks Matt. Share this post Link to post Share on other sites
miamistu 1 Posted January 7, 2007 It's a strip of squishy stuff (very technical, i know). You lay a little between the two surfaces you want to measure the gap in and it'll flatten out to a certain width. Use the little card that comes with the plastigauge to measure that width and you'll know the gap between the surfaces. Share this post Link to post Share on other sites
jim21070 2 Posted January 7, 2007 (edited) Plastigauge is a precision plastic "wire" that compresses when placed on bearing journals and is intened to measure the clearance of the bearing. You measure the clearance by comparing how much the wire has flattened out against a calibrated card. The procedure is to lay a length of plastigauge across say, a crank journal, assemble the bearing to the correct torqure, then strip it and measure the compressed width of the flattened plastigauge against the size gauge supplied with it and there you have your clearance. You must be very careful when using it not to rotate the bearing at all or the result will be meaningless. There is a thread delaing with the rebuild of a 1.6 engine in the Performance area of this forum showing it use. I'll post this and then post the lik to it. EDIT: Here is Frodo Monkey using it... Plastigauge in use Miamistu: Sorry, we were posting at the same time Not trying to steal your thunder... Edited January 7, 2007 by jim21070 Share this post Link to post Share on other sites
boldy205 74 Posted January 7, 2007 to tell you how knackard the bearings are? to tell you weather the crank has been ground before? so if i was to buy new bearings do i actually need to use it? thanks Matt. Share this post Link to post Share on other sites
jim21070 2 Posted January 7, 2007 to tell you how knackard the bearings are? to tell you weather the crank has been ground before?so if i was to buy new bearings do i actually need to use it? thanks Matt. To tell you if your bearing running clearances are in specification during a rebuild, nothing else. It is not recommended to see if your crank is worn. For this you need a micrometer to measure the crank journals. Typically it would be used with a known good crank and new shells to confirm the running clearances are correct. Share this post Link to post Share on other sites
boldy205 74 Posted January 7, 2007 im still not sure why its used. is it to see if the bearings are knackard? or to work out what size new bearings you need? are they used on new or old bearings? thanks for all the replies, im not totaly understanding it!! Share this post Link to post Share on other sites
M3Evo 0 Posted January 7, 2007 As said, it's used to measure the clearance between the bearing shell and the crank journal. Say you stripped your engine at 200k miles, plastigauged it and then measured the result, you'd likely find that the clearance was quite large. So then (ignoring the state of the crank) you buy some new standard sized bearings, install them, and plastigauge the assembly again. You've eliminated the wear in the bearings from the equation now, but you might still find the clearance to be too large. As a final step, you have the crank reground and buy undersized bearings to match. You plastigauge the assembly again and this time, the clearance should be spot on. That's not necessarily the procedure to follow but hopefully it explains what the stuff's used for (although probably not) Share this post Link to post Share on other sites
jim21070 2 Posted January 7, 2007 im not totaly understanding it!! No worries. Bearings like crank mains and big ends have a specified clearance between the journal and shell. This clearance is very tiny (ony a few thou) but is essential to prevent bearing seizure and to allow room for an oil film to be established. Plastigauge is one method of measuring this clearance during a rebuild. If the clearance is too tight the bearing will seize and cause the shells to spin (a spun shell) whereas too large a clearance will cause premature wear, possible knocking and low oil pressure. A crank is best checked for serviceability by using a micromenter to accurately measure the journal diamater, to check for journal ovality and taper. An "Eyeball" examination for excessibe scoring and other journal damage compliments the measurements. Measurements made should be compared to published specifications for the crank in say, the appropriate Haynes Manual. Shell are replaced as a matter of course. They should not, as a rule, be resued during a rebuild. Eyeballing them will show damage and wear on them in the form of scoring, pitting general wear. How the shells wear can give a clue to crank condition but an experienced eye is needed. Share this post Link to post Share on other sites
boldy205 74 Posted January 7, 2007 ah ha! yes indeed it does. thanks for all the replies. just wanted to check before going ahead. suppose thats whats the forums for! Share this post Link to post Share on other sites
frodo_monkey 0 Posted January 7, 2007 Its very easy to use as well - have a look at the pics in my thread. Took me ages to find somewhere that sells it though - try www.debben.co.uk or www.agriemach.co.uk if you struggle Share this post Link to post Share on other sites
boldy205 74 Posted January 7, 2007 I have been reading your progress report, thats what made me think about it. looking good by the way. did you have the head chemical dipped? if so do you mind saying how much it cost? Also, this is all a bit of topic but, the water pump being pierced by a hear bolt if you dont use the correct spacer thing, is this only related to the 8valve enginges or the MI16 as well? Thanks! Matt. Share this post Link to post Share on other sites
frodo_monkey 0 Posted January 7, 2007 (edited) I can't remember how he cleaned the head - I believe he dipped it but can't be sure. The head cost me £250 which was for porting and polishing, time on the flowbench, welding-up an area on the cam housing that was broke and fitting/shimming up a 279 CatCam (not included in the £250, obviously ). He also cut 3-angle seats and spent a bit of time on the valves. Frodo Edited January 7, 2007 by frodo_monkey Share this post Link to post Share on other sites
