M20B28 engine help

Post Tue May 28, 2013 8:10 pm

Hi all, some of you may remember my B28 dying last yr, well the autopsy and rebuild has know begun. heres a recap of my spec and what happened.

built a B28 using the m52b28 crank, M20B20 rods, 2.5 pistons. head has a newman 290 cam, ss manifold and exhaust. she was running fine and well like this no issues at all, year later replaced the head as mine had the typical M20 crack, and put on a BBTB at the same time. again she was a amazing drive then about 4-6 weeks later it all changed. she just packed up on me. we found a broken spark plug (never seen one like that before EVER). youl find a pic here on the original post

http://www.e30zone.net/modules.php?name ... highlight=

so know ive started ripping it all apart. piston 2 is obviously no longer a piston and had a exhaust valve stuck in it. the rest all look fine, however they all had some metal shavings/fillings on top of them.

on the head inlet valves from chamber 2 onwards all are bent or something is keeping them open very slightly. chamber one all looks to be fine.

i had thought it might have been the timing but it was 100% using the original m20b25 timing marks. the timing was checked about 3 times by me and my brothers.

im lost as to why this would have happened. i want to know why to avoid this happening again. hope someone can help

Post Tue May 28, 2013 8:12 pm

Did you do a squish test on the build to see how much clearence there was between the valves and pistons?

Post Tue May 28, 2013 8:20 pm

Rav335uk wrote:Did you do a squish test on the build to see how much clearence there was between the valves and pistons?

no i did not and the car did run fine for just over a year apart from a rocker arm breaking.

Post Tue May 28, 2013 8:26 pm

Did the belt slip??

Post Tue May 28, 2013 8:30 pm

Would the original Timing Marks be applicable, considering the Cam you used?

Post Tue May 28, 2013 8:34 pm

Rav335uk wrote:Did the belt slip??

no it did not that is what i had thought.

Post Tue May 28, 2013 8:37 pm

gooner1 wrote:Would the original Timing Marks be applicable, considering the Cam you used?

from what i was told the original markings will be fine.

Post Tue May 28, 2013 8:38 pm

this is the newman cams spec sheet i had used the 290/290 cam

http://www.newman-cams.com/pdf/bmw.pdf

hopefully some on here can make sense of it as i don't understand it

Post Tue May 28, 2013 8:40 pm

im still thinking if it was a timing issue it would have happened a long time a go not after 12 months

Post Tue May 28, 2013 8:41 pm

Sounds like a stuck or dropped valve.

Stuck: obvious really, gets held open, piston hits on the upstroke.

Dropped: either the valve becomes detached, or the head of it comes off.

Any debris floating about in one cylinder can migrate its way around to any of he others, via the inlet valve, inlet manifold, then another inlet valve

Pm on its way.

Post Tue May 28, 2013 8:48 pm

maggspower wrote:Sounds like a stuck or dropped valve.

Stuck: obvious really, gets held open, piston hits on the upstroke.

Dropped: either the valve becomes detached, or the head of it comes off.

Any debris floating about in one cylinder can migrate its way around to any of he others, via the inlet valve, inlet manifold, then another inlet valve

Pm on its way.

could it be that the valve snapped, the debris from it moved to the others, and also got caught on the inlet seats causing the compression to leak through them? meaning the whole engine dying would be down to one valve snapping?

Post Tue May 28, 2013 8:49 pm

aceifty wrote:this is the newman cams spec sheet i had used the 290/290 cam

http://www.newman-cams.com/pdf/bmw.pdf

hopefully some on here can make sense of it as i don't understand it

Not bad prices either, ooked at the M30 ones.

Byrons right, it looks to be a broken valve.

Post Tue May 28, 2013 8:54 pm

yh there good cams, newman are a very good manufacturer aswell, and i did enjoy that cam.

there is a broken exhaust valve on number 2

Post Tue May 28, 2013 8:55 pm

aceifty wrote:
maggspower wrote:Sounds like a stuck or dropped valve.

Stuck: obvious really, gets held open, piston hits on the upstroke.

Dropped: either the valve becomes detached, or the head of it comes off.

Any debris floating about in one cylinder can migrate its way around to any of he others, via the inlet valve, inlet manifold, then another inlet valve

Pm on its way.
could it be that the valve snapped, the debris from it moved to the others, and also got caught on the inlet seats causing the compression to leak through them? meaning the whole engine dying would be down to one valve snapping?

Yes, that exactly.

Post Tue May 28, 2013 9:25 pm

so know just need to know why the f**k the valve snapped!!

Post Tue May 28, 2013 9:27 pm

My bets still on the belt slipping.

Post Tue May 28, 2013 9:31 pm

so was mine but before i took it all apart the timing was spot on, not a tooth was off

Post Wed May 29, 2013 12:10 am

Rav335uk wrote:My bets still on the belt slipping.

Rav you f****** cowboy! If it was the belt it would have taken more than one valve

Post Wed May 29, 2013 12:18 am

Come on then Mr expert.
Rather than taking the time to.post having a go at me lets have your input to the problem.

Post Wed May 29, 2013 12:26 am

Your a bit touchy tonight

Post Wed May 29, 2013 12:42 am

Not at all.
I want to see your answer.

Post Wed May 29, 2013 5:10 pm

here are some pictures of the damage.

the first thing i had found was number 2 spark plug, the other bit came out the exhaust.

i had put in another spark plug before removing the head and it had got jammed in. the spark plugs at first where a bitch to open.
picture of the head

and finally pictures of the piston.

Post Wed May 29, 2013 5:21 pm

Fook me!!,i have never seen a sparkplug with that damage before!

Post Wed May 29, 2013 5:21 pm

This happened to me back in the day.

http://www.e30zone.net/modules.php?name ... highlight=

Post Wed May 29, 2013 5:24 pm

^^^^yep ,id say thats exactly whats happened to this chaps engine

Post Wed May 29, 2013 5:47 pm

I still have the piston, on display in my man cave.

Post Wed May 29, 2013 6:11 pm

The main thing to remember now is before you rebuild the new engine make sure there is nothing left in the inlet or exhaust manifold!!!!

Post Wed May 29, 2013 6:57 pm

?Needs to be machine cleaned.
simple valve failure then.

Post Wed May 29, 2013 7:05 pm

Rav335uk wrote:?Needs to be machine cleaned.
simple valve failure then.

Yes I would say get a pressure washer in it at least

At a best guess I would say yes, but I would be checking the inlet tract for clues. Its rare for fatigue to get the valves as they are made from high grade steel, but it does happen.

Post Wed May 29, 2013 7:11 pm

Maybe high revs would cause this without the proper balancing of engine components.

Post Wed May 29, 2013 7:16 pm

as im using a 290 cam would the standard valve springs be up to the job

Post Wed May 29, 2013 7:40 pm

aceifty wrote:as im using a 290 cam would the standard valve springs be up to the job

It depends how high the engines red line is set, and how often its used. The correct valve springs are, the lightest poundage to remain in control of the valve and combat valve float at the highest revs that the engine is designed for. Valve float is when the cam and valve spring are no longer in control of the valve, it will bounce off its seat and is generaly bad for an engine. It can feel like hitting a rev limiter. IIRC the standard springs in good condition are good for 7000rpm.

Too strong a spring, leads to premature wear, and BHP loss in frictional forces.

How much extra lift is quoted on the cam?

Post Wed May 29, 2013 8:20 pm

maggspower wrote:
aceifty wrote:as im using a 290 cam would the standard valve springs be up to the job
It depends how high the engines red line is set, and how often its used. The correct valve springs are, the lightest poundage to remain in control of the valve and combat valve float at the highest revs that the engine is designed for. Valve float is when the cam and valve spring are no longer in control of the valve, it will bounce off its seat and is generaly bad for an engine. It can feel like hitting a rev limiter. IIRC the standard springs in good condition are good for 7000rpm.

Too strong a spring, leads to premature wear, and BHP loss in frictional forces.

How much extra lift is quoted on the cam?

iv put a newman cam spec link on page 1 if it helps, i looked at it but got lost

Post Thu May 30, 2013 5:56 pm

im thinking of going up in size of the valves, will i notice much difference

i know the head will need some work to take the valve, but am i write to say the pistons will need work as well.

Post Thu May 30, 2013 8:13 pm

aceifty wrote:im thinking of going up in size of the valves, will i notice much difference

i know the head will need some work to take the valve, but am i write to say the pistons will need work as well.

The only way to know for sure is to do a dummy build. You have a cam with a higher lift, and a valve with a larger diameter and a head that will have had a skim, it would be a brave man that told you that it would be fine, without checking.