Machining questions and other questions for 7mgte rebuild.

[D51208]

Howdy there, I have some questions in relation to an engine I want to rebuild sitting in my basement. I believe it is an 89 7mgte that is stock. It came out of a car that was running. I was told about 130-150K on it. The crank and rods appear to be forged, I have heard from a member here on another of my posts this is supposed to be stock. I have searched quite a bit for the answers and while I have found some answers a lot of the information I have found has been conflicting.

1. Metal head gasket. I was pricing out metal headgaskets and the wording for the listing on it (titan) sounds like if the stock headgasket hasnt blown up, it should be good to go on without decking. Well do I need to get it decked or not? Any sure way to tell? The block and the head, or just the head? Leave the timing cover on, I know that much. I will be getting ARP studs as well.

2. Connecting rods. I have read that the stock rods are beast and can handle 600+ forever. I have also read that you shouldnt really push virgin rods over 500hp off the crank. Well preferably, someday, if I feel the urge, :biglaugh: might want to step over the 500hp threshold. Any way to keep the stock rods and have them shot peened and stress relieved? Anything else? Whichever route would be the most productive money wise.

3. ARP rod bolts. Have to get the rods resized, right? What are the benefits?

4. ARP main studs. What would need to be done, benefits?

5. Pistons and boring. When buying pistons should I just get standard rings and pistons? Oversized a wee bit? Bored?

Oh, planned on replacing bearings. What do you all recommend. I have heard ACL's. I have also heard that clevite 77's are re-boxed


6. What are things I need to check to make sure everything is good?


I apologize if this post is beating many dead ponies from other threads, but at the very least it will serve as a collaborated post for others in the future. I admit, I havent searched #5 and 6 yet due to time constrictions.


Any other random information you want to tell me, I'm game for that too.

 

[hvyman]

1. Machine the block as well. ESP if your rebuilding it. Only costs a little more.

2. Stock rods are good. And forged stock. But eagles are cheap. And for 500 ho should really upgrade with the 7m.

3. Yes the rods will need to be resized. Benefits are better and stronger clamping force. Usually after market rods already come with them.

4. The mains would have to be lined bored and is a good idea anyway. Benefits are stronger and more clamping force.

5. When buying pistons take block to machine shop and have them tell what size you need. Best to machine to the next availble size. You don't much if a gain if at all with boring on these engines. Acl or clevites are good bearings.

6. Harness test the head. Block and head should both be machined to 30ra or better. Find a quality machine shop not the cheapest.

 

[BryanDyer]

Running a titan MLS here. It just a relabeled cometic basically.

 

[D51208]

Thanks for the information! Now for the bad news....


Well, got the block down and pulled rods and pistons. Bearings have pretty much spun. Visible and feel-able with finger nail damage to bearings, rods and crank. Number 6 cylinder has damage too. Worth dickerdoodiling around with fixing or should I just buy other stuff?

I found a line on JE 83.5mm pistons, Eagle rods and potentially a 7m but probably a 6m crank that has been polished and balanced for less than a grand. It was vague whether the pistons and rods were balanced with the crank too. Would this be a better route? Would the rings/bearings be reusable or would I have to buy new? Any concerns I should have? Are the ARP rod bolts in the eagles reusable? What would need to be done to put that crank in my block? I know the cylinders will have to be bored, will there be room to rebore if god forbid something happens and I need to re bore in the future?

Again, thanks for the help.

 

[raysupra]

I see any ARP bolts being reusable. If you ever have a motor tore down far enough for new rings/bearings.. whynot? their not that expensive. Take the time and make it fresh. I have a 6m Crank in my 7m.. I believe it was pretty common and IIRC is a Stock fit so should just be PNP.
How much bore to .20? .40? depends how much you start with. I'm not an expert on boring though.
I had my Crank Balanced to 10k rpm.. And I believe balancing pistons/rods is just making everything to the closest similar weight possible.
I have Shot-peen stock rods.. and am about to be shooting for 750 ish WHP and that is the absolute max I am comfortable with. for stock I wouldn't feel comfortable with 600 maybe 550.. people have pushed 750 or so on stock before but its only a matter of time.
If I could go back I would've put some Carillos or any H beam rods.
Anyone who is machining your block should be able to give you good information on more machining process's and tolerances.. try and call around some rebuilders/machine shops and ask around.

 

[Scooter7M]

Depending on the year of your engine will determine what crank you have. Up till 88 the 7m block got the 6m crank. After that, the 7m crank was made. The difference is a counter weight on the 2 and 5 journal for a better balance.

I just rebuilt mine so I can tell you this from experience. The crank and rods are forged. The pistons are the weak point as they are cast. Replace them and you're good for about 700~ hp. Replace the rods with h beams and you're good for 1000~hp.

Clevites can be had for a decent price, but theyre actually NDC bearings in the clevite box. It's a coated, trimetal bearing. Those or acl are great bearings. Don't let someone try and sell you king bearings, they're garbage.

The block needs to be decked with the rear timing cover torqued as well as the tensioner bolt torqued. A torque plate isn't necessary but recommend if you're going for high power.

 

[D51208]

Thanks for the information scooter. The seller said he had marked everything in regards to the balance. However, when I asked about the marks on the sides of the pistons and if he could feel them his answer was: "...the scoring on the pistons is from initial start up." Thoughts and opinions on this?