a few rebuild questions

[88supraproject]

hey guys,

im rebuilding my 7m and when i pulled the head off i noticed the pistons are .50 over. it looks like they are factory toyota pistons but the o/s .50 ones. how much is this going to affect my compression ration? i have a 2mm stopper head gasket and the block and head are gone to get machined right now for the hg but now im wondering how much the o/s pistons are gonna raise my compression? most of my mods are in my sig but i doubt it matters to much. if anyone has any thoughts on this it would be greatly appreciated.

thanks, adam

 

[87M-GTE]

The only thing that would effect your compression ratio is the amount of material taken off of the head and block when it was machined and the HG you selected. Oversized pistons won't effect compression ratio.

The only way you could measure it is by taking the measurement of the cyl. head, block and the HG. theres a sticky somewhere about HG selection and how it effects your comp. ratio.

edit:
http://www.supramania.com/forums/showthread.php?97552-Head-Gasket-thickness-selection


Sam

 

[88supraproject]

thanks for the help. i have read threw that thread a few times now i was just curious about the piston sizing, thanks for clearing that up.

 

[88supraproject]

hey i have another quick question.. i was looking at my crank today and the edges of it near the connecting rods have a blue shade to them. im assuming that means it has been over heated? should i try and find a new crank or will it be fine? ill try and get some pictures up tonight..

thanks

 

[87M-GTE]

Potentially. The crank should be ok if it did overheat.
I would be worried about the bearings. You might want to check those.

Post up some pics

Sam

 

[IJ.]

.5mm aka +20 thou, it will raise the compression a tiny amount but nothing to worry about, the blue on the crank is from the induction hardening that Toyota did when they made it.

 

[88supraproject]

thanks alot for all the advice you guys are really helpin me out on this. my bearings are all silver still but some have scratches in them and the crank is in good condition im going to get some pictures up tonight so you guys can check them out and let me know.

thanks again

 

[88supraproject]

here are 2 really bad pictures of the worst connecting rod bearing. can some one tell me if i should replace them? ill get some better ones up tommorow

 

[CyFi6]

Picture of the crank shows us virtually nothing. The bearing wear doesn't appear to be terrible, but if im not mistaken there is some copper showing.

Regardless of bearing condition they ALWAYS should be replaced with a rebuild. They are a wearing part and would be like putting an engine back together with old seals and gaskets. Everything should be measured/machined accordingly.

 

[88supraproject]

thanks for your advice cyfi6, ive never replaced rod and main bearings before how do i go about measuring them to find out what size bearing i need? im sorry but i have been reading on replacing them for a few weeks now but i don't fully understand which size bearings to get and what to tell my machine shop to machine. could somebody explain how i should go about changing the rod bearings? thanks alot sorry for any inconvenience. no one in my area has ever worked on a 7m before so im trying to get all the information i can so my machine shop doesn't ruin my motor.

adam

 

[87M-GTE]

You use the existing bearings with plastigauge.
Tighten everything down in the torque sequence, then remove all of what you just tightened in the de-torque sequence, now you measure the plastigauge on the bearings. You add the measurment of the plastigauge to the size of the bearings on the car, from there you now know what size bearings to get.

Correct me if I am wrong, but Im almost positve thats how its done.

Sam

 

[88supraproject]

thanks alot man, but my pistons/rods are already out of the block. is their a way i can measure the bearings without putting everything back in? and also the reason i didnt measure it with plastiguage when i was disassembling it is because i had read a few posts where people are saying not to use plastiguage for some reason.

thanks again

 

[maj75]

You should be able to take the crank to any reputable machine shop and have them measure the crank. If need be, they can machine the crank for the proper clearance. They should be able to tell you what size bearings you need.

 

[88supraproject]

ok thanks i will do that. another thing.. all my connecting rod bearings say std on them so im assuming somebody has replaced them already with a standard size set. am i going to run into any problems now with to much being taken off or anything?

thanks again