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CRM250AR Top end refresh
Posted: 07 Jul 2015, 22:01
by gregorious77
So here is the thread that all AR owners have been waiting for...................... maybe.
After a whole load of hassle finding a std bore piston (thought to be unavailable) I found one and have it in my possession.
Wossner part number 8071D040 Dia 66.33mm clearance 0.07mm
I purchased it from Off Road Only but I think Tom at Leisure Trail (brilliant help with tech knowledge while I was sourcing this piston)* will get a couple to stock now he knows they are available again so you could order all of the required gaskets and piston from them.
*
As was Knackered Mk1
As I knew this was coming I decided to start the strip down.
My bore had brown streaks down it and the piston had some blowby and the whole lot was covered in a fair bit of oil including the bottom end.
Bore (oily)
Brown streaks
Piston
Exhaust side (evidence of 4 corner seize)
Inlet side (evidence of 4 corner seize)
Re: CRM250AR Top end refresh
Posted: 07 Jul 2015, 22:04
by gregorious77
Re: CRM250AR Top end refresh
Posted: 07 Jul 2015, 22:14
by gregorious77
Took the cylinder to work and cleaned it up in our parts washer then used scotchbrite in a criss cross pattern followed by electrical contact cleaner and clean rags and finished with a blow out using compressed air and finally WD40 and clean rags. NOTE - never hone a plated bore.
https://www.youtube.com/watch?v=vaFp8aYkHNA
Resulting bore is shiny and streaks are barely visible.
PV got the treatment too.
Head cleaned up with a rag and some WD40.
Re: CRM250AR Top end refresh
Posted: 07 Jul 2015, 22:22
by gregorious77
Measured a high calorie performance piston to see if it would fit.
Alas it was too big so an overbore and greaseproof paper lining would be required.
Needed silicon so rebuild only got as far as piston on rod tonight.
Re: CRM250AR Top end refresh
Posted: 07 Jul 2015, 23:17
by mekros
I'm interested to see what the high calorie piston rings look like.
Re: CRM250AR Top end refresh
Posted: 08 Jul 2015, 00:43
by jim157
mekros wrote:I'm interested to see what the high calorie piston rings look like.
Re: CRM250AR Top end refresh
Posted: 08 Jul 2015, 20:51
by mekros
Let me know how the run in goes with that lot. lol
Re: CRM250AR Top end refresh
Posted: 09 Jul 2015, 09:52
by admin
epic post in true PB style. nice one fella. watching with interest
Re: CRM250AR Top end refresh
Posted: 09 Jul 2015, 09:54
by admin
what's the difference in weight between the 2 items ?
Re: CRM250AR Top end refresh
Posted: 09 Jul 2015, 12:50
by gregorious77
sorry didn't weigh them.
Ran her up last night though. sounded a bit knocky maybe a bit of pinking due to higher compression.
Ill see what she is like once run in.
Re: CRM250AR Top end refresh
Posted: 28 Jul 2015, 16:27
by admin
how is she running pal ? all ok i hope
Re: CRM250AR Top end refresh
Posted: 28 Jul 2015, 17:10
by gregorious77
Strong and fast but rattles like a diesel. Guessing clearances are a bit on the loose side so getting piston slap. Gonna run it like this and look at bore and plate +2mm later on.
Re: CRM250AR Top end refresh
Posted: 28 Jul 2015, 17:13
by admin
lol brilliant
so you reckon the plating was worn a bit too much or the piston just isnt as snug a fit as the OE one was ?
Re: CRM250AR Top end refresh
Posted: 28 Jul 2015, 17:22
by gregorious77
Plating looked good. There is a b and c sizes oe though so I guess it was the biggest size bore to start with. I have a spare barrel but it has a few dinks in the top sealing surface.
Re: CRM250AR Top end refresh
Posted: 03 Aug 2015, 23:00
by gregorious77
Purchased a whole engine for spares. New bore and piston with 5 miles on it. Failed newly rebuilt crank though. I will strip the crank and do my damndest to discover the origin of the illusive rod through accurate measurement and hours and hours of research.