Keith (type26owner) Can you Help - Cylinder Bore finish

[carrierdave]

Hi Keith
I will be removing my engine shortly (next month) and will be replacing the pistons (thanks to Hamish) and having the block rebored skimmed etc.
I am sure that you have made some previous comments relating to the surface finish of the bores; I think it was in relationship to the piston rings and their ability to spin on a previous post.
So when I select the right machine shop to bore out the block, what finish should I specify for the bores?

Any other tips, idea's and reccommendations whilst I'm spending some money would be welcome.

Thanks

David

PS Apologies to anyone else out there who can answer this; I will be more than happy to hear from you all.

[type26owner]

Hi Dave,
You really need to call the engineering folks of whatever brand of parts you're using and ask that of them. That's their job afterall to ensure the customer is satisfied. Suggest you be upfront and tell them you don't know what you're doing exactly. They will appreciate knowing that and take the time to explain the details so you're empowered with the knowledge. It's the best practice way to operate.

Even if you tell the shop folks the proper finish tolerance that does not guarantee you've gotten it. Ask the shop if they have a surface profiler to measure the finish before you accept it. This surface finish stuff gets complicated. Here's an overview of the callouts now that we've moved into the digital age for instance.
http://www.predev.com/smg/parameters.ht ... 0Roughness

[carrierdave]

Hi Keith,
Thanks for the note. Is there any particular make of piston ring you would reccommend or ones that you would avoid. The last set I picked up had a copper coloured top ring and chrome middle ring - not sure if that was a gimmic or actually improved things (they were Lotus supplied rings).

The other thing I was considering was line boring. In your experience does this need to be done - What causes the big end caps to wear in such a way and should I have it checked.

Thanks

David

[type26owner]

David,
I used Hepolite pistons and rings the last time. IIRC, at least one compression ring is chrome plated. They must not be babied or the possibility of glazing the cylinder walls looms. Dyno oil only of course because some friction is necessary to bed the rings.

Proper break-in procedure is one of those topics of conversation you'll want to run past the engineer for advice.

Line boring is only called for if something is wrong with the block were it's warped out of shape. You can check that stuff out which should always be performed when doing a rebuild with a simple straight-edge and feeler gages. I've installed four cylinder sleeves in these blocks before and have never had a problem with warpage. Usually it's not a problem because the block is so stout.