Some random M20 machine shop questions

[Cinnabar325is]

Have a few questions for a motor that's being built at the shop right now.

1) What is the stock valve spring rate? I'm sure somebody will suggest that we just test them against each other, but that won't do us any good if they're all 20% less than new.

2) What is the lift on a stock B25 cam? I've seen people quote 9.95mm, 10.1mm, and 10.4mm. They are symmetric correct? Same lift for intake and exhaust?

3) What is the tolerance for the big end rod diameter? I know for many American engines, .0005" is acceptable.

Thanks.

[digger]

http://www.e30tech.com/forum/showpost.php?p=938336&postcount=138

[jlevie]

As to the bearings, main bearings come in three "colors" and rod bearings in two "colors. With each "color" having a different ID. You measure the journal diameter and pick the "color" need to get the correct clearance as the table in the Bentley or TIS indicates.

[Cinnabar325is]

Great cam info there, Digger! Was that checked with a brand new B25 cam?

It appears that the inlet lift is about 10.1mm and the exhaust lift is 9.9mm. It was my understanding these are symmetric cams, however. Any thoughts regarding that?

As to the bearings, main bearings come in three "colors" and rod bearings in two "colors. With each "color" having a different ID. You measure the journal diameter and pick the "color" need to get the correct clearance as the table in the Bentley or TIS indicates.

Sorry, I was asking about the diameter of the actual rod on the crankshaft end. They are out of round and need to be resized. I'm looking for a tolerance spec on the diameter. Can't find anything like that in the Bentley.

[digger]

Great cam info there, Digger! Was that checked with a brand new B25 cam?

It appears that the inlet lift is about 10.1mm and the exhaust lift is 9.9mm. It was my understanding these are symmetric cams, however. Any thoughts regarding that?

Sorry, I was asking about the diameter of the actual rod on the crankshaft end. They are out of round and need to be resized. I'm looking for a tolerance spec on the diameter. Can't find anything like that in the Bentley.

i used the unrooted part of the lobe on the outside edge. usually they wear in the middle. it can be finicky getting the dial gauge positioned to capture the true peak it is easier to get timing events. i remember paying particular attention to it so i was confident it is correct. all the exhaust lobes for above cams were done without resetting measurement tools so relative it is as exact as it can be, same with inlet lobes

some independent data suggesting that lift is not the same though there is a slight discrepancy with the peak values which might simply be wear

[Cinnabar325is]

i used the unrooted part of the lobe on the outside edge. usually they wear in the middle. it can be finicky getting the dial gauge positioned to capture the true peak it is easier to get timing events. i remember paying particular attention to it so i was confident it is correct. all the exhaust lobes for above cams were done without resetting measurement tools so relative it is as exact as it can be, same with inlet lobes

some independent data suggesting that lift is not the same though there is a slight discrepancy with the peak values which might simply be wear

Makes sense to me. Thanks again.

[jlevie]

Sorry, I was asking about the diameter of the actual rod on the crankshaft end. They are out of round and need to be resized. I'm looking for a tolerance spec on the diameter. Can't find anything like that in the Bentley.

You get that from the "color" table for oversized bearings.

[richard.bratton]

I use .0003" as a maximum tolerance for big end out of round check.

[Cinnabar325is]

You get that from the "color" table for oversized bearings.

I use .0003" as a maximum tolerance for big end out of round check.

Thanks guys and without having the Bentley nearby at the moment, I vaguely remember the bearing table may have corresponded to the .0003" just listed. ?