Piston and bore question

[redline19]

I have a redtop sr and I think the rings are starting to go, not totally sure but I want to replace it anyway. I've been researching, and seems like the original bore of the sr is 86mm with about .02mm of tolerance? I've been looking at pistons and most come in 86.5mm which is a bit oversized, from cp, je, weisco etc. these slightly oversized ones are pretty cheap like 500 bucks around , but I don't want to be reboring or doing any machine work to the engine.

So if I want pistons that just drop in, I should be going with the 86mm Toda or HKS pistons, but they're quite pricey at about 900-1100 dollars. So I was wondering if anyone knew after any piston that would be a bit cheaper and would just drop right in with the standard SR bore size and if the pistons kit with the complete kit of rings, wrist pins etc are all I need when just replacing the pistons. Should I be looking to also replace some bearings or anything while the engine is apart, besides say a 1.2 metal head gasket and possibly head studs.

thanks in advance

[180fan]

those pistons are oversized (86.5)

I think JE had some pistons that were standard size. Instead of the toda or HKS rings, you can go call CP pistons and ask them to make you a set of 86mm pistons. I'm using CP's and like them alot.

If you've got the engine apart, replace the bearings. You'll be glad you did (assuming you did the sizing right lol).

[GripR]

you don't have to bore it, it's not a huge gap you can hone it.

[redline19]

you don't have to bore it, it's not a huge gap you can hone it.

oh really? I would suspect that honing wouldn't be as much as boring of course. But would that also have to be sent out to a machine shop to do, or would a competent mechanic be able to handle this? and just curious, whats the ball park on honing for say a 86.5mm piston, since it isn't oversized by much. thanks

[redline19]

If you've got the engine apart, replace the bearings. You'll be glad you did (assuming you did the sizing right lol).

you have cp pistons and replaced the bearings, what kind did you put in? and yea the sizing i have no clue how to do, guess i'll do some research on that also.

[180fan]

cleavite t77 bearings. had a line bore done and crank work done so my bearing sizes are nowhere near any of the standard sizes. lol

[redline19]

Look at the bottom of the block and the front of the crank.

On the block: You'll see 5 numbers ranging from 0 to 3 or 4 I think. There might be a letter in the front but it's on a flat recessed part of the block. Write those down.

On the crank: From the front you'll see two sets of numbers, 5 at the top and 4 below the 5. The 4 numbers are the bearing grades you need for each of the rods. Left to right corresponds to rod 1 to 4.

grade school math: Take the two sets of 5 numbers and line them up so the left hand side numbers from the block are above the left hand side number from the crank. Now add downwards. Ex: block reads 12321 and crank reads 01232

so you'd get:main 1: 1 + 0 = you need grade 1 bearingmain 2: 2 + 1 = you need grade 3 bearingetc. Get it? Using one size bearing for a motor that needs different sizes unless it's been main had been line bored and the crank uniformly cut is a really really REALLY bad idea.

nice write up 180fan. considering I don't have the engine apart, and all this bearing tolerances seem to scare the living crap out of me, should I just leave it alone? I'm not really looking to really go nuts on the hp, and I've read that the stock bottom end besides the piston rings are pretty good already.

I'm just looking to replace the pistons w/ the rings along with the metal head gasket to have a nice reliable engine. Would new main and rod bearings really be necessary?

[180fan]

man that was a while back when there were rebuilds up the wazoo with everyone spinning bearings lol. Takes me back to old days...*does the wayne and garth thing with the flashbacks*

well it's really your call. I figure you're you're down there, might as well just have it done. It's not too bad and as long as you're following the math, it's pretty easy. Just check it over by hand with the bearings lubed with whatever assembly lube you like (I recommend redline but motor oil will work fine too). If it turns out you're sweating bullets because the crank's not spinning freely by hand (the crank by itself) then you can resize or go back to your old bearings to make you feel better. I had problems sizing my rod bearings the first time around but luckily I was able to swap em out for the right size ones. I was off by two sizes because my hand was going down and I couldn't tell when I was running my hand across the damn spreadsheet with the part numbers. lol. Good luck and change your oil pump for sure. I nearly spun another bearing when my oil pump went out after I rebuilt my engine. It's enough of a pain to make a man cry.

[redline19]

thanks man, awesome info. i'll basically play it by ear. But I don't really forsee too much of a problem with just replacing the piston and not running a very high hp. But its always good to know what your options are.

anyway, this s13 redtop is my spare motor. I've replaced it with a s14blacktop like half a year ago. Its just sitting at my mechanics and I just wanna fix it up and keep it in my garage if I were to ever need it. but yea, thanks for all the help

[zippitta]

Honing will not oversize your bore. All it does is ruff up the cylinder walls a little so that your piston rings will seat properly. You can purchase a honing tool at just about any auto parts store, sears, etc. If you are putting new pistons in there it is a good idea.

As for finding 86mm pistons, JE, Wiesco, any of them can make them. You just have to call and order them. They advertise the 86.5mm and 87mm because those are the most popular and they are stock piled. Find out which company you want to go with and order the pistons to your specs...

As for the question about the bearings, Yes, replace them. They are relatively inexpensive and it would behoof you to go on ahead and replace it while the motor is apart.

Suggestion on the pistons.... I would go with Wiesco. A lot of people choose JE because of the name, but in personal experience (and talking with other people who have gone with JE), JE tends to egg out. Last I heard it was something that JE is currently working out.

[redline19]

As for the question about the bearings, Yes, replace them. They are relatively inexpensive and it would behoof you to go on ahead and replace it while the motor is apart.

haha "behoof," I actually had to look that work up . Anyway, I was just about to leave the bearing alone since I don't know much about it and I believe they are still in good shape, But since you mentioned it, I'll put some more thought about replacing them out. They just have such crazy tolerance and whatnot and picking the wrong one can screw everything up. Since the motor is being working on by an ordinary mechanic, I'm not sure if leaving it up to them is the right choice. And with sending it out to a machine shop, it would be more money.

As far as pistons go, I finally found 86mm JE pistons available, but now that you mentioned them and also in ohter posts ppl have had unpleasant experiences with the pistons, I guess I'll consider the other manufacturers. But how bad can JE pistons really be? unless you're going really crazy with the hp? They can't be as bad as the stock pistons... who knows

but thanks for all the info. i'll be rethinking this whole setup once again

[zippitta]

I really like Wiesco...check them out. They can custom make any piston you want.

[redline19]

I also heard good things about the CP Pistons. I might just go with their 86.5mm ones since I could just hone it to have it seat right. Also some sites, like you said, have them overstocked and are really cheap, like under 400 bucks. So my options in pistons are pretty good right now.

[zippitta]

Just remember that honing is not boring. To use 86.5mm pistons you will have to have your block bored by a machine shop. All honing does is put a cross-hatch on the cylinder walls. Honing takes about as much metal off as 400grit sand paper would.

[redline19]

you don't have to bore it, it's not a huge gap you can hone it.

ah I must of understood that wrong then. lucky I won't really have downtime on it sinces its a spare motor, so I'll have plenty of time get all the facts/ spec etc down before I delve into this project.

Thanks for clearing it up

[zippitta]

glad I could help. If you have any other questions just ask.

[pampadori]

CP makes the 86mm bore too. pm me if you want a set still.

[VitaminT]

Yeah I was going to say I called Road Race Engineering in FL and they can get them in 86.0mm for like $537. Said it would take like 1-2 weeks.

[yellow_jacket]

If you are really that scared of the bearing tolerances, at least get some plastigauge and check them.

Personally I can't imagine spending money for pistons and rings, and then leaving the same bearings in. If you read up a bit more, I believe you will find that most SR's go because of bearing failures on the bottom end. If you really want a realiable motor, getting new bearings is the way to go. I think I just paid under a dollar for each stick of plastigauge I bought. Autozone actually stocks the stuff.

As for the piston size and clearances, while you've got it apart go ahead and check the bore.

[spider_slayer]

just get a set of stock pistons. its 200 for a set and they can withstand an incrediable amount of abuse and will be the proper bore. same goes for the rods.