bore wear limit 3.9 low comp?

[twinpipes]

Does anyone know the wear limit on a low comp/38D 3.9? My bores are 94.12 mm thats 4.8 thou in old money, would these glaze-bust and re-ring,what do you think.I am fitting a new cam in it,and thinking of real steels viper cyclone DW252,a cloyes street true roller timing set,and will I need uprated valve springs with this cam? all advice welcome many thanks twinpipes!!!

[mgbv8]

You might have a problem getting a Cam out of Real Steel at the moment.

I've just tried and been told that the guy who does the cam grinding has left so they dont expect to have any cams ready until next year (ish)

This was for a Blower Cam. But it might be worth trying to see if they have any other stock on the shelf.

[twinpipes]

Thanks for the reply perry I like the Bgt,my older brother had a many B/s a 64 pull handle roadster,british racing green with a roll cage jag wires bucket seats loads of race numbers stuck in the boot,I think it was someones hill climb classic before he got it in about 79/80,it went well but not quite as quick as yours, and felt very tight,although I never drove it I was only 16.He also had midgets,a frogeye sprite and 4 or 5 Bgts.I have not had the pleasure of owning a mg yet but realy like them,you never know when the range rover has to much tin worm I might use the engine in a B of my own.I have been tempted many times on a purchase but not took the plunge yet.If I manage to get a viper cyclone cam from realsteel do you think I will need uprated springs or will I get away with stock springs,and do you think the bores are passed it with almost 5 thou oversize.Let me know what you thinks and thanks again twinpipes!!!

[mgbv8]

Personally I would not be worried with 4-5 thou clearance in the bores.
I'm pretty sure that the expected piston to bore gap on a fresh engine is about 2-3 thou ??

So your 4-5 thou is only a couple of thou of wear I guess. If it was my engine I would rough hone the bores with a glazebuster and then index all the rings to each bore and piston for correct ring gaps.

Last year we found a scrap RV8 engine for my Sons Escort. It cost nothing so we had nowt to lose. It had oval bore wear evident at the top of the bores. Top side of the bores was smooth. Bottom side there was a definate ridge where the top ring ended its travel. We glazebusted until the ridge was gone. Fitted the rings and gapped them all as you should. The engine has since run with no smoke at all and good compression. This is a pure race engine mind!! It only ever runs at low speeds in the pits and then get hammered to death on the drag strip. It revs happily to 6000 and is still going strong. Due to it having open headers you cant hear any engine noise

Did you measure the bores about 2" down or at the top?
Did you measure the bores at right angles to the wrist pins?

If you do get that cam it should drop in assuming the engine hasnt been skimmed or decked in the past. Regarding the valves I have always had the guides machined down to take a 1/2" lift on all RV8's I've ever done for myself and friends. This gives you the option to go a bit bigger on the cam at a later date?


Perry

[DaviesDJ]

Many people run an extra thou clearance in the bores - deliberately - it is sometimes seen to lower friction ambiguous opinions differ

[twinpipes]

I have both a glazebuster or carborundum hone,which would you prefer to use.I will try realsteel on monday with regards cam and order some new rings then.Many thanks twinpipes!!!

[kiwicar]

Hi
If you have a proper carborundum hone use that, a glaze buster is a good substitute but not as good as the real thing.
Best regards
Mike

[mgbv8]

I have both a glazebuster or carborundum hone,which would you prefer to use.I will try realsteel on monday with regards cam and order some new rings then.Many thanks twinpipes!!!

I use this. I have different grades of stone to go with it as well.
Once you get the hang of it with a low speed drill you can get the cross hatching marks pretty darn good at 45 degree's

http://www.ebay.co.uk/itm/Cylinder-Hone ... 1034779669

[twinpipes]

Thats the very same hone I have infact I think I have two.Thanks for all your help,I will let you know how the rebuild proceeds,twinpipes!!! P.S. I have ordered the parts from realsteel and they have got the viper cyclone cam in stock.Has any of you lot used this camshaft,its realsteel DW252, it has :433" of lift both inlet and exhaust I think the lobe seperation is 108 degrees but not sure any info regarding specs or performance of this cam much appreciated.I am using bulleted guides,waisted stem valves,headman headers,a bit of porting on the heads,tin head gaskets with a slight head skim,Arp studs,twin exhaust pipes all the way through apart from an X piece that comes together were the original y piece was.I am hoping I have chose the right camshaft.Many thanks twinpipes!!!

[mgbv8]

If you are using tin gaskets with a head skim and a slightly bigger lift make sure you check the valve to piston clearance when building??