Printable Version of Topic

Click here to view this topic in its original format

6G Celicas Forums _ Engine/Transmission/Maintenance _ 7A-FE connecting rod bolts

Posted by: Langing Dec 9, 2017 - 3:33 PM

Beginning to rebuild my Celica ST 7A-FE engine (finally).

Page EG-132 of the repair manual asked me to measure the DIAMETER of the connecting rod bolts (at the measuring point - some 20 mm from the head of the bolt).

They specify the standard diameter: 8.860 - 9.000 mm (0.3488 - 0.3543 ")

And the minimum diameter: 8.60 mm (0.3386")

My bolts measured about 7.22 mm (0.284"), which is less than the minimum, which means I need to buy new bolts.

Then I checked my Haynes manual and found they had a different minimum bolt diameter spec of 0.2992". Still, my bolts are 0.015" smaller than the minimum and I still need to buy new bolts, BUT. . .

The Toyota manual spec seems so much larger than my bolts, AND the Haynes manual spec is quite close, so I question whether Toyota has a mistake in their manual, and would like to know if anybody has a correct spec for this bolt, or can tell me where I might find it. I am suspecting that I would not get much help if I called Toyota. Maybe I am wrong.

Posted by: Smaay Dec 9, 2017 - 10:39 PM

you are doing a good job at reading the specs and following directions. Toyota manuals i use as gospel over a haynes or chiltons. Now here is my 17+ years of experience in building toyota engines. use the original bolts. unless you are building a monster HP engine out of a 7A, use the original bolts and save your money. this is a 7A you are building. its not a high revving engine, it dont make any power. you will be just fine.

Posted by: Bitter Dec 10, 2017 - 10:51 AM

My advice is going to be opposite but I haven't been building engines like Smaay has. The bolts cost less than a hole in the block on the side of the road in winter at 2AM, change the bolts. Time and aggravation has a price and for me that's a higher cost than some bolts.

Posted by: Langing Dec 10, 2017 - 5:49 PM

Late at night, on the interstate, she just shut completely down, unexpectedly. All my fault, of course, because I had let the instrument cluster light go so dim I could not read it. Coasted to a stop on the side of the highway, with no lights or power, barely in front of a State Trooper, luckily. Steam was pouring out of the engine. . . with help from the trooper I was able to get a tow to put her into my driveway. The point is, what happened to her was an extreme heat event that blew out the head gasket such that there was no compression in any cylinder.

Long before that night, I had run a lawn mower without oil and know the damage that can come from engine overheating. That time the piston 'seized' to the cylinder wall so it could not be moved at all. In my Celica's case, the pistons did not seize to the walls of the cylinders, but I imagine that they expanded due to the intense heat and probably created a lot of friction (or drag) being in contact with the cylinder walls. That makes me believe that the connecting rod bolts experienced enough force to cause them to stretch during the event, which would translate into their measured undersized diameter. I had already ordered new bolts from the local dealer before getting a response here (about $58 for 8 freaking bolts). I have a chance to return them before they arrive, but I am kinda of Bitter's mind-set, afraid of having something worse happen should I trust those bolts, though I sincerely appreciate your voice of experience, Smaay, and admit that my engine is not a work-horse and isn't going to be abused.

I originally posted to ask if anyone knew whether the spec in the BGB was incorrect, being that my measured diameter was so far below the specified worst case diameter. My Haynes manual is in line with the spec on that bolt for the other engine (5S?) in my BGB, so I kinda think the 7A spec is incorrect. It would be nice to know. It is my first experience rebuilding, and I am trying to learn every thing I can during the experience.

I have another 'burning' question to ask, concerning engine balancing, but think I had best post it at the top level, so it gets seen by people with that kind of experience.

Thanks again for your kind responses.

Posted by: Smaay Dec 10, 2017 - 10:16 PM

now that i know you grossly overheated the engine. I suggest replacing it. the 7A is not worth the money it costs to replace everything. just find a replacement, or upgrade to a better engine

Posted by: Langing Dec 11, 2017 - 9:34 AM

QUOTE (Smaay @ Dec 10, 2017 - 10:16 PM) *
now that i know you grossly overheated the engine. I suggest replacing it. the 7A is not worth the money it costs to replace everything. just find a replacement, or upgrade to a better engine

I should have asked for your opinion back when it happened. I already ripped out the engine, tore it down, cleaned all the parts, got a refurbished head and all the parts I thought I would need to overhaul the 7A-FE block, and have been working on doing everything necessary to rebuild it.

Frankly, I find it taxes my abilities just to do this simple and straight-forward rebuild task and cannot imagine undertaking any mods whatsoever to upgrade to a better engine. At least at this point in my development. I am treating this effort as a learning experience on a 'learner car' cause the car and engine is virtually worthless on the market. Unless I get the car running again, all the money spent is 'sunk' cost. Prior to the engine problem, I had completely rebuilt the suspension, bearings, ball-joints and brake system, so once it is running it should be 'good to go' for another 300 k miles if I can fix its interior to where I can stand driving it.

Posted by: njccmd2002 Dec 11, 2017 - 12:04 PM

if you are doing this as a learning experience, there is no limit to cost, as what you learn you apply in other cars...

Powered by Invision Power Board (
© Invision Power Services (