valve guides M103
 

Need an educated guess here. The machine shop reconditioning my head and valves needs parts with head to expedite the service.

My question is, which size valve guides should I order if my engine is not burning oil? There's the standard size, then a slightly oversize guide I assume that's needed when guides start to rattle around -- not my case I don't think.

Do you think the standard size would press in fine on a 206,000 mile engine?

Thanks!

~Paul

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'91 300E, 206k miles

UNLESS the guides "fall" out of the cylinder head always use the std size! The oversize is OUTSIDE dia. not the inside.

The key with guides is an appropriate interference fit as they are pressed in. As it turns out the standard guides are oversize anyway. Years ago the the true standard guides were available. As example a the outside diameter of your guides will be about 14.01mm. The standard replacement will be 14.05mm. The guides are also available in 14.20mm and 14.40mm.

If a guide is loose in the head or assembles too easy then a larger guide is necessary. I think MB would have you broach the hole in the head to the appropriate ID. This is a very dangerous procedure as there is no going backward. An old MB tech told me 25 years ago how to do it safely. You cut the larger guide to a little bigger than the hole on a lathe (this sometimes requires trial and error with the loss of a guide or two). Then you drive it in with at least as much force as the good ones (since the hole is deformed a tighter than normal fit will be required). The head hole will be slightly ovalled and the guide will be forced to the shape. They won't come out. After this the inner diameter must be sized by reaming to the proper diameter.

The added size of the new guides will work in all holes that the old guides were firmly installed.

Paul
 

It's quite simple.Either you are dealing with an unqualified machine shop or you're getting in the middle of things.If they tell you what they need, trust them to do their job.If they're asking you for advice find another machine shop.A good experienced machinist can measure accurately and tell you what fits in what hole.Hope this helps.

Peter

What are the clearances for valvestem to guide on the M103?

Cap'n
 

Don't know exactly,but it doesn't matter because you can't measure clearances with the valve train intact.With the head off the car and the springs off,you could check latteral movement witha dial indicator.The most accurate test is to remove the valve and slide what's called a go no go gage in the hole.If the no go end slides into the guide, it needs to be replaced.
Peter