Rebore or not..

[dkw_dude]

Hi forum
I had a cambelt failure recently and have sent the cylinder head to an engine shop for changing bent valves and general refurbishing. I found the reason why the cambelt snapped, an object got between the belt and the crank belt pulley

Right before this happened i did a comrpession test, all cylinders were at ~9-10 Bar. The engine uses no oil or water (the head was off ca 2 years ago, and new oil gaskets and a steel head gasket installed). On the basis of these facts I would like to reassemble the engine as it is.

But the engine has run approx 190k miles (mostly sensible driving), and I can feel some cylinder wear, especially in cyl. no 1. At 10mm or so down the cylinder bore I can feel a "smooth edge". The rest of the cylinders also have this, but it feels like they are less worn.

The car has a rs2 setup, and the plan is to keep it that way. So, what would you do, leave the block as it is and reassemble the engine, or send it to the engine shop to check it up?

Cheers, Leif Helge

[Ross]

Your risk of course, and I doubt anyone would recommend leaving it without knowing how much wear there is!

Personally, my motor with 150k, was found to have a slight 'lip' like yours (majority of the stroke aparrently still had visible honing marks) and I was recommended by experienced mechanics and an engineering firm to rebore, and of course I followed that advice. Yeah it's an expense, but a warranted one I feel. Perhaps, your best bet is to get the wear measured so you can get a better idea of how severe it is.

Cheers
Ross

[ottawa coupe]

last year i pulled a 7A apart and if had that "lip" you're describing. i was told the best and safest would be to rebore. the lip on mine was not even all the way around the bore suggesting it had gone oval. as well, if you were to put new rings in, they would likely break on that lip as the rings would be bigger than the old ones so there would be more interferance when they hit that lip.

measure the wear and if it still lies within the original bore tolerances, leave it alone UNLESS you're putting new rings in. if you're doing the rings then bore regardless and hope you don't have to bore it so much as to require bigger pistons!!! and if you plan on being buried with the car, why not just bore it out now as a "while I'm in there" job?

[DJones]

Mine had done 208k took it to the machine shop it only had 1000 of wear limit is 3000 so just fitted new rings after honing.

[dkw_dude]

Yeah, I guess I must measure cylinder wear. But the car is a long way from machine shops, is there a way I can do this by myself? Is this device ok for measuring (for scandinavian forum members):

http://www.verktygsboden.se/?id=68203

[caterpillar]

i have a bare block.....from a s2 with no wear in......intr???

[diesel des]

If it was useing no oil and had good compression whats the problem. Get the head back on and drive untill it does use oil or have low compression. At that time have it reboared. All you will waste is the price of the gasket you will use now.

In the mean time save up for new pistons and rods so when it does start getting tired you have all the best bits in stock ready to go.

[dkw_dude]

Thanks for the feedback, that's what I'm thinking of doing. But I am a little worried about the wear in cyl 1, can too much clearance between piston and cylinderwall cause the piston to vibrate, and cause the knock sensors to pick up a "false signal"? Car has felt low on power, like its holding back ignition (lambda values were ok, WB lambda installed).

[diesel des]

I think the piston would need to be really floating arround to do that. It cant be that bad if the comprerssion is good and not useing oil.

[dkw_dude]

Just a question, at which power level is it recommended to reduce compression? Just in case I rebore it and want to prep it for higher power levels. I have purchased a second car, so I can take my time on this job if I have to

[caterpillar]

i have bare blocks,who DONT need rebore......81,00 bore(std) 2,2 or 82,5(2,3) or 83,00......!!! send med PM or sms(90101651) have a 3b bottom too

[diesel des]

It depends on the octane of your fuel. Stock CR should be ok with 400 + BHP on good fuel and mapping.

[dkw_dude]

measurement..

Have had the wear measured, bore was 81,11 on the worst cylinder (right under the "lip"), 1 cm down the bore it was 81,04. Don't know the wear limits but I hope it's ok?? The guy who did the measurement said he believed so, but he has little experience with this type of engine.

[DJones]

Cylinder dia 80.98 bore 81.01 deviation from nominal dimesions max 0.08 ie no more than 81.09 bore.

[magarv]

Have had the wear measured, bore was 81,11 on the worst cylinder (right under the "lip"), 1 cm down the bore it was 81,04. Don't know the wear limits but I hope it's ok?? The guy who did the measurement said he believed so, but he has little experience with this type of engine.

I got Sarpsborg Motorverksted to measure my block. They have all the data you need and i´m sure they will tell you if you give them a call. They are very helpfull.