OzVMX Forum

Clubroom => Tech Talk => Topic started by: OverTheHill on July 24, 2013, 08:00:49 pm

Title: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: OverTheHill on July 24, 2013, 08:00:49 pm

Have done some odd ball mods & got away with them over the years but here's the "Stupid question Bit". I know my Briggs lawn mower [4 stroke] runs an alloy bore & lived to an old age so--i have a stuffed GYt Kit Cylinder & am bloody tempted to try getting it bored to take a first over DT1MX piston kit i have [or would it last 5 minutes--or less]. bottom line is it would have to go a lot bigger to fit a liner so nothing lost. Lawn mower is slow revving & lots of oil of course but i could run lots of mixed fuel anyway. Loved those chrome cylinders--just never went off song after a few laps like cast liners seemed to & stayed strong & sharp to the end. Ok, i'm back in the corner now!!. ps, can chrome 'be' bored off or is it chemically removed first?

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: tony27 on July 24, 2013, 08:38:00 pm

Normally stripped.
There's a company down south that has a good reputation for rechroming cylinders, I know a couple of guys who have had cylinders done by them & they are really happy
http://www.nzcylinders.com/

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: OverTheHill on July 24, 2013, 09:46:44 pm

thanks Tony, looks an interesting site, i'll have a read.

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: Mike52 on July 25, 2013, 08:34:28 am

Briggs have special rings to run in the ally.

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: tony27 on July 25, 2013, 08:35:01 am

Contact Phil Grant at Norsewear/NZ Natural if you want to know more, he had a couple of cylinders done for his red rocket last year or earlier this year

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: Tahitian_Red on July 25, 2013, 08:44:22 am

A bigger problem than re-plating might be finding stock bore iron rings.  Do they come up on eBay very often?

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: Davey Crocket on July 25, 2013, 09:32:34 am

We have just had an issue (twice) with a re-plated barrel on a YZ250A. It appears the new plating is too hard for the std Yamaha chrome bore rings....just rips them to shreds so to speak. We are looking at a modern ring that will fit the skinny Yamaha piston grove. We don't know if it's because the NOS rings are 40 years old or just to soft as they are a non chrome ring.....head fark.....doesn't help your situation but may save you some dollars......re-sleeve my friend.... ;D

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: pancho on July 25, 2013, 09:35:35 am

 I think Briggs&S engines' alloy bore is anodised, which I understand is basically an electrical process like electro plating, not only used for colouration of aluminium but also for forming a hard wearing skin.

 Running similar metals together like aly or stainless etc doesn't work.

cheers

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: John Orchard on July 25, 2013, 10:26:02 am

Just to answer the original question, the KDX400 I have here was running fine, plenty of compression, but during the transplant of the engine into a 250 frame I thought I'd tear it down to make sure all was good inside.

The Electro-Fusion bore had worn through all around the intake port and a large amount alloy was showing on down the exhaust side of the bore, the alloy was polished smooth and still seamed to be useable?

Lucky I pulled it apart, it had cracks above the gudgeon pin, the piston crown would have come of soon.

So I too was wondering if engines could happily run in an alloy (uncoated) bore?

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: Lozza on July 25, 2013, 10:52:55 am

..........for the umpteenth time............

Yamaha/Honda 'chrome' bores have plain uncoated cast iron rings, those rings are only compatable with the chrome(hard like on forks). I don't know anyone replating with this process now

Nicasil /Electrofusion needs a chrome faced ring the same ring as used in a cast iron bore. If you have a chrome bore now and can't find rings, find a piston and/or rings that are the correct bore size. Have the cylinder replated with nicasil. Done.

Honda had a CBR900 that ran on a uncoated bore , the coating on the ring was never disclosed
 

Title: Re: Stupid Question about the DT1 GYT Kit Chrome Bore
Post by: OverTheHill on July 25, 2013, 06:16:47 pm

Lozza gotta ask--you say cbr900 run uncoated bores--as in alloy piston straight on alloy bore? am i thinking right. If i risk going ahead i'd use a .25 or .50 piston & ring from a DT1mx which had a cast iron bore & [are they?] a chrome ring!!, has a green coated surface. Made the dumb mistake with my chrome gyt cylinder which was buggered anyway [worn off around ports & at tdc still ran rattly but ok] mistakenly sorted through 'best of the rest' rings & thought i found a non-chrome ring but bloody hell, just ripped it to bits in 5 minutes---lasted 45 years [1968] & i STUFFED IT. Probably won't get it re-plated as too stingy with money, just thinking out loud. Have a regular running cylinder with a wiseco or la sleeve co 'sleeve' in it & will watch ebay for a sleeve. Sleeve in this other one had a bridged exhaust port. In my [ignorant] youth i cut the bridge out & is still going ok 35/40 years later albeit now needs to go out to 1st over but a real good material looking sleeve. Thanks.