32 replies to this topic

[tuktuk]

took my mini to get tuned the other day, only to find it was down on compression on cylinder 4 by 30%

engine has only covered 150 miles since being bored to 1330, new pistons and rings ect...

took the head off tonight to find a gap/hole between the valves on number 4. poured brake fluid into the ports and it leaked through between the valves.





also, on the same cylinder, i found this nick in the piston... could this be related ?



my question is, can the gap between the valves be repaired, or is it scrap ? i have no problems chucking a few hundred monies at it if it will work again, but if its probably not going to work i will just buy an equivelant spec head.

[ginigwunkle]

yes you can get them repaired, if theres enough material there......

have you had the valves out and seen if its cracked through?

what you can get is ardox overcheck......spray it on the area and wipe it off if there are hairline cracks it will stain them....needs to be very clean first though....

the brake fluid may have just seeped through a poorly seated valve....in which case lapping the valve back in will sort that out!

[tuktuk]

valves are still in. theres a definite hole there, although its not clear on the pic

taking it to get looked at tomorrow, see if thees anything can be done.

[Sprocket]

That is cracked. It can be repaired, but looking at the size of those valves it will go again. If there is parts of the casting missing from that area and breaking the valve seal, then it could be an issue, but if its all there and just cracked, it will be fine. The BR Group A Rally head i have is cracked across the valve seats, i had the valves re cut and now there is no noticeble difference in compression readings.

Im hazarding a guess that there are no hardened seats fitted? judging by the size of the valves

If you are intending to do road mileage on a head it would be more suitable to run 37/29mm valves with hardened seats at the very most. Thus reducing the likelyhood of this happening

[Guess-Works.com]

Also allowing the head/engine to get up to temperature before you open up the engine will help.

[tuktuk]

most people im talking to, are reccomending i dont go for something as big this time.

looking at MED's site, they do a 36inlet with i think 31exh for 550, think il go for that... more money to fork out

[CraigyBoy]

bitt off topic, but just wondering, I have a cylinder head with 29mm exhaust and 33.5 mm inlet, what stage is this equivelant too, it also has bronze guides and doubles.


Thanks

[Guess-Works.com]

Stage Standard, they are standard valve sizes for any non performance 1275 head.

However, valve sizes are not as important compared to the shaping of the inlet and exhaust ports... No point having whooping great valves if the ports don't flow the gasses..

[Sprocket]

looking at MED's site, they do a 36inlet with i think 31exh for 550, think il go for that

is that absolutely nescisary on a 1330? again id still be tempted to go for what would be considered 36/29mm valves giving the best comprimise of reliability and performance.

Ultimately the decision is yours.

[tuktuk]

its not neccesary no(but we only live once ), i mean this car is going to replace my daily driver when that comes off the road. it will do about 30odd mile a day in rush hour traffic which i doubt it will be happy about, but then when the daily driver is back on the road, i have a well powered weekend car (hopefully).

the price between stg4 and stg 3 isnt alot, so i might aswell go for the higher spec, or so i keep telling myself

[samwell]

but listen... as gw said, you're betting off spending the money on the porting of the head than purely going after valve sizes. You have already experienced one failure, why don't you learn from your lesson, i'd be surprised if you can spot the difference.

Sam

[CraigyBoy]

you say the head i have is standard, but when comparing valve sizes to the head that was originally on my engine, the exhaust is 29mm, so the same, but the inlet is only 31mm, and this new head has 33.5mm and porting work.


so is 33.5mm standard?

the original head is off my 1275 A+, out of a metro.

thanks..

Edited by CraigyBoy, 23 April 2008 - 04:44 PM.

[CraigyBoy]

anyone?

[T.Harper]

you say the head i have is standard, but when comparing valve sizes to the head that was originally on my engine, the exhaust is 29mm, so the same, but the inlet is only 31mm, and this new head has 33.5mm and porting work.


so is 33.5mm standard?

the original head is off my 1275 A+, out of a metro.

thanks..

that's odd. What cylinder head casting is the original, it may be a small bore head such as a 12G206 or 12G295 modified to have larger exhaust valves. Valves sizes on these were inlet 31mm (1 7/32 in) and exhaust 25.4mm (1inch)

[The Matt]

anyone?

You could start your own topic?