20 replies to this topic

[Shifty]

I've just bought an engine block and it appears to have a problem!!

When you rotate the crank back and forth the centre thrusts move back and forth as well.

Pulled the centre cap off and the thrust tab doesn't locate into the bearing housing.

Its an early A series with a centre strap.

Are the thrusts different between A+ and A?

Is this normal????

Its been a while since I pulled an engine apart, however I don't remember this happening??

I can't put any pics up at the moment as my camera battery is dead.

Any Thoughts?

[Jordie]

how much does it move? Like all the way around? or just a few mm back and forth?

[Shifty]

About 5mm either way, so 10mm in total

The thrust just doesn't seem to be locating in the main bearing cap?

[Jordie]

Strange as it shouldnt really move that much.

By the top half moving 5mm in one direction, this must be moving the lower half around by 5mm too.

Is it the same on both sides of the cap? And are the thrusts fitted the right way. The face with the knotches out is facing the crank on both sides of the cap.

[Shifty]

Yup, same both sides.

I've got a suspicion that the wrong thrusts have been fitted.

Even more concerning is that is was built by "professional" company!!

I'll get some pics up tomorrow.

[Jordie]

I think all the thrusts are the same, but I may be wrong. Normally in std and +003

pics would help. 5mm either way sounds like alot of movement to me.

[Shifty]

I've been doing some digging around and i can't find any reference to them being different?

The block is meant to be an ex racing one, so maybe its been fitted with uprated thrusts?

I'll strip it down tomorrow and take some pics

[Jordie]

Is there any side to side movement on the crank with them fitted?

[Shifty]

Nope, its strange.

Everything else checks out.

Something weird!!!

[miniboo]

so has the centre main been machine flat for a strap? If so then the ears that hold the thrusts in place may have been machined off.

[Shifty]

so has the centre main been machine flat for a strap? If so then the ears that hold the thrusts in place may have been machined off.

Thats another possibility.

By all account the centre strap has been done for a while.

If the ears have been machined off then that the block pretty much scrap isn't it?

[Jordie]

Ive got a centre main strap on my 1380 A-series engine and i have no problems with the thrusts....

[Shifty]

Am I right in saying that the main bearing housings are line bored on the block?

Therefore if the centre cap has been over machined then the block is pretty much scrap as I cant't just replace the centre cap?

I'll have a good look how my centre cap has been machined, may be its a cowboy job?!!!

Edited by shiftyseamus, 14 February 2009 - 06:53 PM.

[Jordie]

you can replace it, but would need it checking and re-line boring if required by a machinist.

[Wil_h]

What has happend is that your cap has been machine wrong, it's a common problem with 998s.

If you machine a 1275 cap you just do it flat, to do a 998 properly you need to take the centre section out leaving the locating slots in place. I have had some very reputable engine builders make this mistake.

If you leave it how it is you wil likely knock the tabs of on the thrusts wrecking the block.

You have a few options:

1) buy a strap from Morspeed that is wider and has the slots machine in it.

2) dowl the cap permanently locating the thrusts.