2.8L M20 build - Now with 2.7L!

[2mAn]

just read the whole thread, was excited at first to see it all come together, but then.... :(

[LJ851]

I guess that is possible. But it wouldn't start happening at 100 miles, it would start a lot sooner than that. The machine shop showed me that it was over 0,1". Well over that, in fact!

In any event, I forgot to post my findings here. The timing belt skipped quite a bit. The cam gear is turned too far clockwise if the crank is at TDC, so that means it was too advanced, correct? I am taking the head off to make sure I don't have any bent valves, but just wondering if that knocking noise could have been preignition due to it being so far advanced instead of rod knock? Here's to hoping!

A tenth of an inch should be fine. Cam timing does not cause preignition, only ignition timing does that. That rattle sounds pretty substantial to me, like a rod knock or similar. What were your rod bearing clearances?

[dinanm3atl]

I believe from talking to Alex he was told it needed to be .08-.1 and his is .15-.2 to guarantee clearance? This is going off memory so I will let him chime in.

[Cinnabar325is]

The distance between the crank and pistons at BDC is about .10".

For a standard M20B25? For a 2.8 stroker as he did (and as I did it) it would depend on how much the machinist shaved off the counterweights. And in my case, the machinist cut it too close and the skirts on 2 pistons just barely skimmed the crank when I turned it by hand on the engine stand. So I got to work with a file on the skirts. Just a little off each where the interference was.

[acolella76]

I guess that is possible. But it wouldn't start happening at 100 miles, it would start a lot sooner than that. The machine shop showed me that it was over 0,1". Well over that, in fact!

In any event, I forgot to post my findings here. The timing belt skipped quite a bit. The cam gear is turned too far clockwise if the crank is at TDC, so that means it was too advanced, correct? I am taking the head off to make sure I don't have any bent valves, but just wondering if that knocking noise could have been preignition due to it being so far advanced instead of rod knock? Here's to hoping!

[Myster-E]

Do you know the distance between your piston skirts and counterweights at BDC? How close were they?

I know mine were darn close, I actually had to do a bit of file work to the skirts (less than ideal I know) to ensure they wouldn't contact.

The distance between the crank and pistons at BDC is about .10".

[Cinnabar325is]

Do you know the distance between your piston skirts and counterweights at BDC? How close were they?

I know mine were darn close, I actually had to do a bit of file work to the skirts (less than ideal I know) to ensure they wouldn't contact.

[Myster-E]

I'm not talking about any pictures. The engine sounded fine at idle but when you put it under load rods and pistons stretch making contact between the pistons and crank.

[acolella76]

Yeah, just wondering, what makes you think the clearance was too tight? That is kind of a bold claim to look at a picture of a piston and crank separately and say that they are too close

[Myster-E]

You will still have to have a minimum gap of .080-.01" between the piston and the crank due to the expanding and stretching of the rod and pistons.

[acolella76]

I'm willing to bet piston to crank contact.

Oh? Even though my pistons cleared the crank just fine?

[MR 325]

Go figure. Still not entirely convinced that my rods are fucked. Wouldn't it still be able to start and run if that was the case? It won't even start now, just kind of stutters like it's not getting any gas.

I'm willing to bet piston to crank contact.

[The Humjet]

Sorry to hear mate. I think the only thing you can do is pull that motor out and get it onto an engine stand and start by pulling off that sump. This thread was going so good its a real shame its come to this :(

[Chruby99]

ouch hope it is not as bad as it looks

[acolella76]

Go figure. Still not entirely convinced that my rods are fucked. Wouldn't it still be able to start and run if that was the case? It won't even start now, just kind of stutters like it's not getting any gas.